Internet-Draft YANG Data Types and Groupings for Crypto May 2022
Watsen Expires 25 November 2022 [Page]
Workgroup:
NETCONF Working Group
Internet-Draft:
draft-ietf-netconf-crypto-types-23
Published:
Intended Status:
Standards Track
Expires:
Author:
K. Watsen
Watsen Networks

YANG Data Types and Groupings for Cryptography

Abstract

This document presents a YANG 1.1 (RFC 7950) module defining identities, typedefs, and groupings useful to cryptographic applications.

Editorial Note (To be removed by RFC Editor)

This draft contains placeholder values that need to be replaced with finalized values at the time of publication. This note summarizes all of the substitutions that are needed. No other RFC Editor instructions are specified elsewhere in this document.

Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements:

Artwork in this document contains placeholder values for the date of publication of this draft. Please apply the following replacement:

The following Appendix section is to be removed prior to publication:

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 25 November 2022.

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Table of Contents

1. Introduction

This document presents a YANG 1.1 [RFC7950] module defining identities, typedefs, and groupings useful to cryptographic applications.

1.1. Relation to other RFCs

This document presents one or more YANG modules [RFC7950] that are part of a collection of RFCs that work together to, ultimately, enable the configuration of the clients and servers of both the NETCONF [RFC6241] and RESTCONF [RFC8040] protocols.

The modules have been defined in a modular fashion to enable their use by other efforts, some of which are known to be in progress at the time of this writing, with many more expected to be defined in time.

The normative dependency relationship between the various RFCs in the collection is presented in the below diagram. The labels in the diagram represent the primary purpose provided by each RFC. Hyperlinks to each RFC are provided below the diagram.

                               crypto-types
                                 ^      ^
                                /        \
                               /          \
                      truststore         keystore
                       ^     ^             ^  ^
                       |     +---------+   |  |
                       |               |   |  |
                       |      +------------+  |
tcp-client-server      |     /         |      |
   ^    ^        ssh-client-server     |      |
   |    |           ^            tls-client-server
   |    |           |              ^     ^        http-client-server
   |    |           |              |     |                 ^
   |    |           |        +-----+     +---------+       |
   |    |           |        |                     |       |
   |    +-----------|--------|--------------+      |       |
   |                |        |              |      |       |
   +-----------+    |        |              |      |       |
               |    |        |              |      |       |
               |    |        |              |      |       |
            netconf-client-server       restconf-client-server
Table 1: Label to RFC Mapping
Label in Diagram Originating RFC
crypto-types [I-D.ietf-netconf-crypto-types]
truststore [I-D.ietf-netconf-trust-anchors]
keystore [I-D.ietf-netconf-keystore]
tcp-client-server [I-D.ietf-netconf-tcp-client-server]
ssh-client-server [I-D.ietf-netconf-ssh-client-server]
tls-client-server [I-D.ietf-netconf-tls-client-server]
http-client-server [I-D.ietf-netconf-http-client-server]
netconf-client-server [I-D.ietf-netconf-netconf-client-server]
restconf-client-server [I-D.ietf-netconf-restconf-client-server]

1.2. Specification Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

1.3. Adherence to the NMDA

This document is compliant with the Network Management Datastore Architecture (NMDA) [RFC8342]. It does not define any protocol accessible nodes that are "config false".

1.4. Conventions

Various examples used in this document use a placeholder value for binary data that has been base64 encoded (e.g., "BASE64VALUE="). This placeholder value is used as real base64 encoded structures are often many lines long and hence distracting to the example being presented.

2. The "ietf-crypto-types" Module

This section defines a YANG 1.1 [RFC7950] module called "ietf-crypto-types". A high-level overview of the module is provided in Section 2.1. Examples illustrating the module's use are provided in Examples (Section 2.2). The YANG module itself is defined in Section 2.3.

2.1. Data Model Overview

This section provides an overview of the "ietf-crypto-types" module in terms of its features, identities, typedefs, and groupings.

2.1.1. Features

The following diagram lists all the "feature" statements defined in the "ietf-crypto-types" module:

Features:
  +-- hidden-keys
  +-- password-encryption
  +-- private-key-encryption
  +-- symmetric-key-encryption
  +-- one-symmetric-key-format
  +-- one-asymmetric-key-format
  +-- cms-encrypted-data-format
  +-- cms-enveloped-data-format
  +-- certificate-expiration-notification
  +-- symmetrically-encrypted-value-format
  +-- asymmetrically-encrypted-value-format
  +-- certificate-signing-request-generation

2.1.2. Identities

The following diagram illustrates the relationship amongst the "identity" statements defined in the "ietf-crypto-types" module:

Identities:
  +-- public-key-format
  |  +-- subject-public-key-info-format
  |  +-- ssh-public-key-format
  +-- private-key-format
  |  +-- rsa-private-key-format
  |  +-- ec-private-key-format
  |  +-- one-asymmetric-key-format
  |            {one-asymmetric-key-format}?
  +-- symmetric-key-format
  |  +-- octet-string-key-format
  |  +-- one-symmetric-key-format
  |            {one-symmetric-key-format}?
  +-- encrypted-value-format
     +-- symmetrically-encrypted-value-format
     |  |      {symmetrically-encrypted-value-format}?
     |  +-- cms-encrypted-data-format
     |         {cms-encrypted-data-format}?
     +-- asymmetrically-encrypted-value-format
        |      {asymmetrically-encrypted-value-format}?
        +-- cms-enveloped-data-format
               {cms-enveloped-data-format}?

Comments:

  • The diagram shows that there are four base identities. The first three identities are used to indicate the format that key data, while the fourth identity is used to indicate the format for encrypted values. The base identities are "abstract", in the object oriented programming sense, in that they only define a "class" of formats, rather than a specific format.
  • The various "leaf" identities define specific encoding formats. The derived identities defined in this document are sufficient for the effort described in Section 1.1 but, by nature of them being identities, additional derived identities MAY be defined by future efforts.
  • Identities used to specify uncommon formats are enabled by "feature" statements, allowing applications to support them when needed.

2.1.3. Typedefs

The following diagram illustrates the relationship amongst the "typedef" statements defined in the "ietf-crypto-types" module:

Typedefs:
  binary
    +-- csr-info
    +-- csr
    +-- x509
    |  +-- trust-anchor-cert-x509
    |  +-- end-entity-cert-x509
    +-- crl
    +-- ocsp-request
    +-- ocsp-response
    +-- cms
       +-- data-content-cms
       +-- signed-data-cms
       |  +-- trust-anchor-cert-cms
       |  +-- end-entity-cert-cms
       +-- enveloped-data-cms
       +-- digested-data-cms
       +-- encrypted-data-cms
       +-- authenticated-data-cms

Comments:

  • All the typedefs defined in the "ietf-crypto-types" module extend the "binary" type defined in [RFC7950].
  • Additionally, all the typedefs define a type for encoding an ASN.1 [ITU.X680.2015] structure using DER [ITU.X690.2015].
  • The "trust-anchor-*" and "end-entity-*" typedefs are syntactically identical to their base typedefs and only distinguish themselves by the expected nature of their content. These typedefs are defined to facilitate common modeling needs.

2.1.4. Groupings

The "ietf-crypto-types" module defines the following "grouping" statements:

  • encrypted-value-grouping
  • password-grouping
  • symmetric-key-grouping
  • public-key-grouping
  • asymmetric-key-pair-grouping
  • trust-anchor-cert-grouping
  • end-entity-cert-grouping
  • generate-csr-grouping
  • asymmetric-key-pair-with-cert-grouping
  • asymmetric-key-pair-with-certs-grouping

Each of these groupings are presented in the following subsections.

2.1.4.1. The "encrypted-value-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "encrypted-value-grouping" grouping:

  grouping encrypted-value-grouping:
    +-- encrypted-by
    +-- encrypted-value-format    identityref
    +-- encrypted-value           binary

Comments:

  • The "encrypted-by" node is an empty container (difficult to see in the diagram) that a consuming module MUST augment key references into. The "ietf-crypto-types" module is unable to populate this container as the module only defines groupings. Section 2.2.1 presents an example illustrating a consuming module populating the "encrypted-by" container.

  • The "encrypted-value" node is the value, encrypted by the key referenced by the "encrypted-by" node, and encoded in the format appropriate for the kind of key it was encrypted by.

    • If the value is encrypted by a symmetric key, then the encrypted value is encoded using the format associated with the "symmetrically-encrypted-value-format" identity.
    • If the value is encrypted by an asymmetric key, then the encrypted value is encoded using the format associated with the "asymmetrically-encrypted-value-format" identity.

    See Section 2.1.2 for information about the "format" identities.

2.1.4.2. The "password-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "password-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping password-grouping:
    +-- (password-type)
       +--:(cleartext-password)
       |  +-- cleartext-password?   string
       +--:(encrypted-password) {password-encryption}?
          +-- encrypted-password
             +---u encrypted-value-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping password-grouping:
    +-- (password-type)
       +--:(cleartext-password)
       |  +-- cleartext-password?   string
       +--:(encrypted-password) {password-encryption}?
          +-- encrypted-password
             +-- encrypted-by
             +-- encrypted-value-format    identityref
             +-- encrypted-value           binary

Comments:

  • For the referenced grouping statement(s):

  • The "choice" statement enables the password data to be cleartext or encrypted, as follows:

    • The "cleartext-password" node can encode any cleartext value.
    • The "encrypted-password" node's structure is discussed in Section 2.1.4.1.
2.1.4.3. The "symmetric-key-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "symmetric-key-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping symmetric-key-grouping:
    +-- key-format?            identityref
    +-- (key-type)
       +--:(cleartext-key)
       |  +-- cleartext-key?   binary
       +--:(hidden-key) {hidden-keys}?
       |  +-- hidden-key?      empty
       +--:(encrypted-key) {symmetric-key-encryption}?
          +-- encrypted-key
             +---u encrypted-value-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping symmetric-key-grouping:
    +-- key-format?            identityref
    +-- (key-type)
       +--:(cleartext-key)
       |  +-- cleartext-key?   binary
       +--:(hidden-key) {hidden-keys}?
       |  +-- hidden-key?      empty
       +--:(encrypted-key) {symmetric-key-encryption}?
          +-- encrypted-key
             +-- encrypted-by
             +-- encrypted-value-format    identityref
             +-- encrypted-value           binary

Comments:

  • For the referenced grouping statement(s):

  • The "key-format" node is an identity-reference to the "symmetric-key-format" abstract base identity discussed in Section 2.1.2, enabling the symmetric key to be encoded using the format defined by any of the derived identities.

  • The "choice" statement enables the private key data to be cleartext, encrypted, or hidden, as follows:

    • The "cleartext-key" node can encode any cleartext key value.
    • The "hidden-key" node is of type "empty" as the real value cannot be presented via the management interface.
    • The "encrypted-key" node's structure is discussed in Section 2.1.4.1.
2.1.4.4. The "public-key-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "public-key-grouping" grouping:

  grouping public-key-grouping:
    +-- public-key-format    identityref
    +-- public-key           binary

Comments:

  • The "public-key-format" node is an identity-reference to the "public-key-format" abstract base identity discussed in Section 2.1.2, enabling the public key to be encoded using the format defined by any of the derived identities.
  • The "public-key" node is the public key data in the selected format. No "choice" statement is used to hide or encrypt the public key data because it is unnecessary to do so for public keys.
2.1.4.5. The "asymmetric-key-pair-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "asymmetric-key-pair-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping asymmetric-key-pair-grouping:
    +---u public-key-grouping
    +-- private-key-format?            identityref
    +-- (private-key-type)
       +--:(cleartext-private-key)
       |  +-- cleartext-private-key?   binary
       +--:(hidden-private-key) {hidden-keys}?
       |  +-- hidden-private-key?      empty
       +--:(encrypted-private-key) {private-key-encryption}?
          +-- encrypted-private-key
             +---u encrypted-value-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping asymmetric-key-pair-grouping:
    +-- public-key-format              identityref
    +-- public-key                     binary
    +-- private-key-format?            identityref
    +-- (private-key-type)
       +--:(cleartext-private-key)
       |  +-- cleartext-private-key?   binary
       +--:(hidden-private-key) {hidden-keys}?
       |  +-- hidden-private-key?      empty
       +--:(encrypted-private-key) {private-key-encryption}?
          +-- encrypted-private-key
             +-- encrypted-by
             +-- encrypted-value-format    identityref
             +-- encrypted-value           binary

Comments:

  • For the referenced grouping statement(s):

  • The "private-key-format" node is an identity-reference to the "private-key-format" abstract base identity discussed in Section 2.1.2, enabling the private key to be encoded using the format defined by any of the derived identities.

  • The "choice" statement enables the private key data to be cleartext, encrypted, or hidden, as follows:

    • The "cleartext-private-key" node can encode any cleartext key value.
    • The "hidden-private-key" node is of type "empty" as the real value cannot be presented via the management interface.
    • The "encrypted-private-key" node's structure is discussed in Section 2.1.4.1.
2.1.4.6. The "certificate-expiration-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "certificate-expiration-grouping" grouping:

  grouping certificate-expiration-grouping:
    +---n certificate-expiration
            {certificate-expiration-notification}?
       +-- expiration-date    yang:date-and-time

Comments:

  • This grouping's only purpose is to define the "certificate-expiration" notification statement, used by the groupings defined in Section 2.1.4.7 and Section 2.1.4.8.
  • The "certificate-expiration" notification enables servers to notify clients when certificates are nearing expiration.
  • The "expiration-date" node indicates when the designated certificate will (or did) expire.
  • Identification of the certificate that is expiring is built into the notification itself. For an example, please see Section 2.2.3.
2.1.4.7. The "trust-anchor-cert-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "trust-anchor-cert-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping trust-anchor-cert-grouping:
    +-- cert-data?                         trust-anchor-cert-cms
    +---u certificate-expiration-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping trust-anchor-cert-grouping:
    +-- cert-data?                trust-anchor-cert-cms
    +---n certificate-expiration
            {certificate-expiration-notification}?
       +-- expiration-date    yang:date-and-time

Comments:

  • For the referenced grouping statement(s):

  • The "cert-data" node contains a chain of one or more certificates encoded using a "signed-data-cms" typedef discussed in Section 2.1.3.
2.1.4.8. The "end-entity-cert-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "end-entity-cert-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping end-entity-cert-grouping:
    +-- cert-data?                         end-entity-cert-cms
    +---u certificate-expiration-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping end-entity-cert-grouping:
    +-- cert-data?                end-entity-cert-cms
    +---n certificate-expiration
            {certificate-expiration-notification}?
       +-- expiration-date    yang:date-and-time

Comments:

  • For the referenced grouping statement(s):

  • The "cert-data" node contains a chain of one or more certificates encoded using a "signed-data-cms" typedef discussed in Section 2.1.3.
2.1.4.9. The "generate-csr-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "generate-csr-grouping" grouping:

  grouping generate-csr-grouping:
    +---x generate-certificate-signing-request
            {certificate-signing-request-generation}?
       +---w input
       |  +---w csr-info    ct:csr-info
       +--ro output
          +--ro certificate-signing-request    ct:csr

Comments:

  • This grouping's only purpose is to define the "generate-certificate-signing-request" action statement, used by the groupings defined in Section 2.1.4.10 and Section 2.1.4.11.
  • This action takes as input a "csr-info" type and returns a "csr" type, both of which are discussed in Section 2.1.3.
  • For an example, please see Section 2.2.2.
2.1.4.10. The "asymmetric-key-pair-with-cert-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "asymmetric-key-pair-with-cert-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping asymmetric-key-pair-with-cert-grouping:
    +---u asymmetric-key-pair-grouping
    +---u end-entity-cert-grouping
    +---u generate-csr-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping asymmetric-key-pair-with-cert-grouping:
    +-- public-key-format                       identityref
    +-- public-key                              binary
    +-- private-key-format?                     identityref
    +-- (private-key-type)
    |  +--:(cleartext-private-key)
    |  |  +-- cleartext-private-key?            binary
    |  +--:(hidden-private-key) {hidden-keys}?
    |  |  +-- hidden-private-key?               empty
    |  +--:(encrypted-private-key) {private-key-encryption}?
    |     +-- encrypted-private-key
    |        +-- encrypted-by
    |        +-- encrypted-value-format    identityref
    |        +-- encrypted-value           binary
    +-- cert-data?                              end-entity-cert-cms
    +---n certificate-expiration
    |       {certificate-expiration-notification}?
    |  +-- expiration-date    yang:date-and-time
    +---x generate-certificate-signing-request
            {certificate-signing-request-generation}?
       +---w input
       |  +---w csr-info    ct:csr-info
       +--ro output
          +--ro certificate-signing-request    ct:csr

Comments:

  • This grouping defines an asymmetric key with at most one associated certificate, a commonly needed combination in protocol models.

  • For the referenced grouping statement(s):

2.1.4.11. The "asymmetric-key-pair-with-certs-grouping" Grouping

This section presents two tree diagrams [RFC8340] illustrating the "asymmetric-key-pair-with-certs-grouping" grouping. The first tree diagram does not expand the internally used grouping statement(s):

  grouping asymmetric-key-pair-with-certs-grouping:
    +---u asymmetric-key-pair-grouping
    +-- certificates
    |  +-- certificate* [name]
    |     +-- name?                       string
    |     +---u end-entity-cert-grouping
    +---u generate-csr-grouping

The following tree diagram expands the internally used grouping statement(s), enabling the grouping's full structure to be seen:

  grouping asymmetric-key-pair-with-certs-grouping:
    +-- public-key-format                       identityref
    +-- public-key                              binary
    +-- private-key-format?                     identityref
    +-- (private-key-type)
    |  +--:(cleartext-private-key)
    |  |  +-- cleartext-private-key?            binary
    |  +--:(hidden-private-key) {hidden-keys}?
    |  |  +-- hidden-private-key?               empty
    |  +--:(encrypted-private-key) {private-key-encryption}?
    |     +-- encrypted-private-key
    |        +-- encrypted-by
    |        +-- encrypted-value-format    identityref
    |        +-- encrypted-value           binary
    +-- certificates
    |  +-- certificate* [name]
    |     +-- name?                     string
    |     +-- cert-data                 end-entity-cert-cms
    |     +---n certificate-expiration
    |             {certificate-expiration-notification}?
    |        +-- expiration-date    yang:date-and-time
    +---x generate-certificate-signing-request
            {certificate-signing-request-generation}?
       +---w input
       |  +---w csr-info    ct:csr-info
       +--ro output
          +--ro certificate-signing-request    ct:csr

Comments:

  • This grouping defines an asymmetric key with one or more associated certificates, a commonly needed combination in configuration models.

  • For the referenced grouping statement(s):

2.1.5. Protocol-accessible Nodes

The "ietf-crypto-types" module does not contain any protocol-accessible nodes, but the module needs to be "implemented", as described in Section 5.6.5 of [RFC7950], in order for the identities in Section 2.1.2 to be defined.

2.2. Example Usage

2.2.1. The "symmetric-key-grouping" and "asymmetric-key-pair-with-certs-grouping" Grouping

The following non-normative module is constructed in order to illustrate the use of the "symmetric-key-grouping" (Section 2.1.4.3), the "asymmetric-key-pair-with-certs-grouping" (Section 2.1.4.11), and the "password-grouping" (Section 2.1.4.2) grouping statements.

Notably, this example illustrates a hidden asymmetric key (ex-hidden-asymmetric-key) has been used to encrypt a symmetric key (ex-encrypted-one-symmetric-based-symmetric-key) that has been used to encrypt another asymmetric key (ex-encrypted-rsa-based-asymmetric-key). Additionally, the symmetric key is also used to encrypt a password (ex-encrypted-password).

module ex-crypto-types-usage {
  yang-version 1.1;
  namespace "http://example.com/ns/example-crypto-types-usage";
  prefix ectu;

  import ietf-crypto-types {
    prefix ct;
    reference
      "RFC AAAA: YANG Data Types and Groupings for Cryptography";
  }

  organization
    "Example Corporation";
  contact
    "YANG Designer <mailto:yang.designer@example.com>";

  description
    "This module illustrates the 'symmetric-key-grouping'
     and 'asymmetric-key-grouping' groupings defined in
     the 'ietf-crypto-types' module defined in RFC AAAA.";

  revision 2022-05-24 {
    description
      "Initial version";
    reference
      "RFC AAAA: Common YANG Data Types for Cryptography";
  }

  container symmetric-keys {
    description
      "A container of symmetric keys.";
    list symmetric-key {
      key "name";
      description
        "A symmetric key";
      leaf name {
        type string;
        description
          "An arbitrary name for this key.";
      }
      uses ct:symmetric-key-grouping {
        augment "key-type/encrypted-key/encrypted-key/"
              + "encrypted-by" {
          description
            "Augments in a choice statement enabling the
             encrypting key to be any other symmetric or
             asymmetric key.";
          uses encrypted-by-choice-grouping;
        }
      }
    }
  }
  container asymmetric-keys {
    description
      "A container of asymmetric keys.";
    list asymmetric-key {
      key "name";
      leaf name {
        type string;
        description
          "An arbitrary name for this key.";
      }
      uses ct:asymmetric-key-pair-with-certs-grouping {
        augment "private-key-type/encrypted-private-key/"
              + "encrypted-private-key/encrypted-by" {
          description
            "Augments in a choice statement enabling the
             encrypting key to be any other symmetric or
             asymmetric key.";
          uses encrypted-by-choice-grouping;
        }
      }
      description
        "An asymmetric key pair with associated certificates.";
    }
  }
  container passwords {
    description
      "A container of passwords.";
    list password {
      key "name";
      leaf name {
        type string;
        description
          "An arbitrary name for this password.";
      }
      uses ct:password-grouping {
        augment "password-type/encrypted-password/"
              + "encrypted-password/encrypted-by" {
          description
            "Augments in a choice statement enabling the
             encrypting key to be any symmetric or
             asymmetric key.";
          uses encrypted-by-choice-grouping;
        }
      }
      description
        "A password.";
    }
  }

  grouping encrypted-by-choice-grouping {
    description
      "A grouping that defines a choice enabling references
       to other keys.";
    choice encrypted-by-choice {
      mandatory true;
      description
        "A choice amongst other symmetric or asymmetric keys.";
      case symmetric-key-ref {
        leaf symmetric-key-ref {
          type leafref {
            path "/ectu:symmetric-keys/ectu:symmetric-key/"
               + "ectu:name";
          }
          description
            "Identifies the symmetric key that encrypts this key.";
        }
      }
      case asymmetric-key-ref {
        leaf asymmetric-key-ref {
          type leafref {
            path "/ectu:asymmetric-keys/ectu:asymmetric-key/"
               + "ectu:name";
          }
          description
            "Identifies the asymmetric key that encrypts this key.";
        }
      }
    }
  }
}

The tree diagram [RFC8340] for this example module follows:

module: ex-crypto-types-usage
  +--rw symmetric-keys
  |  +--rw symmetric-key* [name]
  |     +--rw name                   string
  |     +--rw key-format?            identityref
  |     +--rw (key-type)
  |        +--:(cleartext-key)
  |        |  +--rw cleartext-key?   binary
  |        +--:(hidden-key) {hidden-keys}?
  |        |  +--rw hidden-key?      empty
  |        +--:(encrypted-key) {symmetric-key-encryption}?
  |           +--rw encrypted-key
  |              +--rw encrypted-by
  |              |  +--rw (encrypted-by-choice)
  |              |     +--:(symmetric-key-ref)
  |              |     |  +--rw symmetric-key-ref?    leafref
  |              |     +--:(asymmetric-key-ref)
  |              |        +--rw asymmetric-key-ref?   leafref
  |              +--rw encrypted-value-format    identityref
  |              +--rw encrypted-value           binary
  +--rw asymmetric-keys
  |  +--rw asymmetric-key* [name]
  |     +--rw name                                    string
  |     +--rw public-key-format                       identityref
  |     +--rw public-key                              binary
  |     +--rw private-key-format?                     identityref
  |     +--rw (private-key-type)
  |     |  +--:(cleartext-private-key)
  |     |  |  +--rw cleartext-private-key?            binary
  |     |  +--:(hidden-private-key) {hidden-keys}?
  |     |  |  +--rw hidden-private-key?               empty
  |     |  +--:(encrypted-private-key) {private-key-encryption}?
  |     |     +--rw encrypted-private-key
  |     |        +--rw encrypted-by
  |     |        |  +--rw (encrypted-by-choice)
  |     |        |     +--:(symmetric-key-ref)
  |     |        |     |  +--rw symmetric-key-ref?    leafref
  |     |        |     +--:(asymmetric-key-ref)
  |     |        |        +--rw asymmetric-key-ref?   leafref
  |     |        +--rw encrypted-value-format    identityref
  |     |        +--rw encrypted-value           binary
  |     +--rw certificates
  |     |  +--rw certificate* [name]
  |     |     +--rw name                      string
  |     |     +--rw cert-data                 end-entity-cert-cms
  |     |     +---n certificate-expiration
  |     |             {certificate-expiration-notification}?
  |     |        +-- expiration-date    yang:date-and-time
  |     +---x generate-certificate-signing-request
  |             {certificate-signing-request-generation}?
  |        +---w input
  |        |  +---w csr-info    ct:csr-info
  |        +--ro output
  |           +--ro certificate-signing-request    ct:csr
  +--rw passwords
     +--rw password* [name]
        +--rw name                        string
        +--rw (password-type)
           +--:(cleartext-password)
           |  +--rw cleartext-password?   string
           +--:(encrypted-password) {password-encryption}?
              +--rw encrypted-password
                 +--rw encrypted-by
                 |  +--rw (encrypted-by-choice)
                 |     +--:(symmetric-key-ref)
                 |     |  +--rw symmetric-key-ref?    leafref
                 |     +--:(asymmetric-key-ref)
                 |        +--rw asymmetric-key-ref?   leafref
                 +--rw encrypted-value-format    identityref
                 +--rw encrypted-value           binary

Finally, the following example illustrates various symmetric and asymmetric keys as they might appear in configuration:

=============== NOTE: '\' line wrapping per RFC 8792 ================

<symmetric-keys
  xmlns="http://example.com/ns/example-crypto-types-usage"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <symmetric-key>
    <name>ex-hidden-symmetric-key</name>
    <hidden-key/>
  </symmetric-key>
  <symmetric-key>
    <name>ex-octet-string-based-symmetric-key</name>
    <key-format>ct:octet-string-key-format</key-format>
    <cleartext-key>BASE64VALUE=</cleartext-key>
  </symmetric-key>
  <symmetric-key>
    <name>ex-one-symmetric-based-symmetric-key</name>
    <key-format>ct:one-symmetric-key-format</key-format>
    <cleartext-key>BASE64VALUE=</cleartext-key>
  </symmetric-key>
  <symmetric-key>
    <name>ex-encrypted-one-symmetric-based-symmetric-key</name>
    <key-format>ct:one-symmetric-key-format</key-format>
    <encrypted-key>
      <encrypted-by>
        <asymmetric-key-ref>ex-hidden-asymmetric-key</asymmetric-key\
-ref>
      </encrypted-by>
      <encrypted-value-format>ct:cms-enveloped-data-format</encrypte\
d-value-format>
      <encrypted-value>BASE64VALUE=</encrypted-value>
    </encrypted-key>
  </symmetric-key>
</symmetric-keys>

<asymmetric-keys
  xmlns="http://example.com/ns/example-crypto-types-usage"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <asymmetric-key>
    <name>ex-hidden-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <hidden-private-key/>
    <certificates>
      <certificate>
        <name>ex-hidden-asymmetric-key-cert</name>
        <cert-data>BASE64VALUE=</cert-data>
      </certificate>
    </certificates>
  </asymmetric-key>
  <asymmetric-key>
    <name>ex-rsa-based-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <private-key-format>ct:rsa-private-key-format</private-key-forma\
t>
    <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
    <certificates>
      <certificate>
        <name>ex-cert</name>
        <cert-data>BASE64VALUE=</cert-data>
      </certificate>
    </certificates>
  </asymmetric-key>
  <asymmetric-key>
    <name>ex-one-asymmetric-based-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <private-key-format>ct:one-asymmetric-key-format</private-key-fo\
rmat>
    <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
  </asymmetric-key>
  <asymmetric-key>
    <name>ex-encrypted-rsa-based-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <private-key-format>ct:rsa-private-key-format</private-key-forma\
t>
    <encrypted-private-key>
      <encrypted-by>
        <symmetric-key-ref>ex-encrypted-one-symmetric-based-symmetri\
c-key</symmetric-key-ref>
      </encrypted-by>
      <encrypted-value-format>ct:cms-encrypted-data-format</encrypte\
d-value-format>
      <encrypted-value>BASE64VALUE=</encrypted-value>
    </encrypted-private-key>
  </asymmetric-key>
</asymmetric-keys>

<passwords
  xmlns="http://example.com/ns/example-crypto-types-usage"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <password>
    <name>ex-cleartext-password</name>
    <cleartext-password>super-secret</cleartext-password>
  </password>
  <password>
    <name>ex-encrypted-password</name>
    <encrypted-password>
      <encrypted-by>
        <symmetric-key-ref>ex-encrypted-one-symmetric-based-symmetri\
c-key</symmetric-key-ref>
      </encrypted-by>
      <encrypted-value-format>ct:cms-encrypted-data-format</encrypte\
d-value-format>
      <encrypted-value>BASE64VALUE=</encrypted-value>
    </encrypted-password>
  </password>
</passwords>

2.2.2. The "generate-certificate-signing-request" Action

The following example illustrates the "generate-certificate-signing-request" action, discussed in Section 2.1.4.9, with the NETCONF protocol.

REQUEST

<rpc message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <action xmlns="urn:ietf:params:xml:ns:yang:1">
    <asymmetric-keys
      xmlns="http://example.com/ns/example-crypto-types-usage">
      <asymmetric-key>
        <name>ex-hidden-asymmetric-key</name>
        <generate-certificate-signing-request>
          <csr-info>BASE64VALUE=</csr-info>
        </generate-certificate-signing-request>
      </asymmetric-key>
    </asymmetric-keys>
  </action>
</rpc>

RESPONSE

=============== NOTE: '\' line wrapping per RFC 8792 ================

<rpc-reply message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <certificate-signing-request xmlns="http://example.com/ns/example-\
crypto-types-usage">BASE64VALUE=</certificate-signing-request>
</rpc-reply>

2.2.3. The "certificate-expiration" Notification

The following example illustrates the "certificate-expiration" notification, discussed in Section 2.1.4.6, with the NETCONF protocol.

=============== NOTE: '\' line wrapping per RFC 8792 ================

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2018-05-25T00:01:00Z</eventTime>
  <asymmetric-keys xmlns="http://example.com/ns/example-crypto-types\
-usage">
    <asymmetric-key>
      <name>ex-hidden-asymmetric-key</name>
      <certificates>
        <certificate>
          <name>ex-hidden-asymmetric-key-cert</name>
          <certificate-expiration>
            <expiration-date>2018-08-05T14:18:53-05:00</expiration-d\
ate>
          </certificate-expiration>
        </certificate>
      </certificates>
    </asymmetric-key>
  </asymmetric-keys>
</notification>

2.3. YANG Module

This module has normative references to [RFC2119], [RFC2986], [RFC3447], [RFC4253], [RFC5280], [RFC5652], [RFC5915], [RFC5958], [RFC6031], [RFC6125], [RFC6991], [RFC7093], [RFC8174], [RFC8341], and [ITU.X690.2015].

<CODE BEGINS> file "ietf-crypto-types@2022-05-24.yang"

module ietf-crypto-types {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-crypto-types";
  prefix ct;

  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types";
  }

  import ietf-netconf-acm {
    prefix nacm;
    reference
      "RFC 8341: Network Configuration Access Control Model";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";

  contact
    "WG Web:   https://datatracker.ietf.org/wg/netconf
     WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>";

  description
    "This module defines common YANG types for cryptographic
     applications.

     Copyright (c) 2021 IETF Trust and the persons identified
     as authors of the code. All rights reserved.

     Redistribution and use in source and binary forms, with
     or without modification, is permitted pursuant to, and
     subject to the license terms contained in, the Revised
     BSD License set forth in Section 4.c of the IETF Trust's
     Legal Provisions Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC AAAA
     (https://www.rfc-editor.org/info/rfcAAAA); see the RFC
     itself for full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2022-05-24 {
    description
      "Initial version";
    reference
      "RFC AAAA: YANG Data Types and Groupings for Cryptography";
  }

  /****************/
  /*   Features   */
  /****************/

  feature one-symmetric-key-format {
    description
      "Indicates that the server supports the
       'one-symmetric-key-format' identity.";
  }

  feature one-asymmetric-key-format {
    description
      "Indicates that the server supports the
       'one-asymmetric-key-format' identity.";
  }

  feature symmetrically-encrypted-value-format {
    description
      "Indicates that the server supports the
       'symmetrically-encrypted-value-format' identity.";
  }

  feature asymmetrically-encrypted-value-format {
    description
      "Indicates that the server supports the
       'asymmetrically-encrypted-value-format' identity.";
  }

  feature cms-enveloped-data-format {
    description
      "Indicates that the server supports the
       'cms-enveloped-data-format' identity.";
  }

  feature cms-encrypted-data-format {
    description
      "Indicates that the server supports the
       'cms-encrypted-data-format' identity.";
  }

  feature certificate-signing-request-generation {
    description
      "Indicates that the server implements the
       'generate-certificate-signing-request' action.";
  }

  feature certificate-expiration-notification {
    description
      "Indicates that the server implements the
       'certificate-expiration' notification.";
  }

  feature hidden-keys {
    description
      "Indicates that the server supports hidden keys.";
  }

  feature password-encryption {
    description
      "Indicates that the server supports password
       encryption.";
  }

  feature symmetric-key-encryption {
    description
      "Indicates that the server supports encryption
       of symmetric keys.";
  }

  feature private-key-encryption {
    description
      "Indicates that the server supports encryption
       of private keys.";
  }

  /*************************************************/
  /*   Base Identities for Key Format Structures   */
  /*************************************************/

  identity symmetric-key-format {
    description
      "Base key-format identity for symmetric keys.";
  }

  identity public-key-format {
    description
      "Base key-format identity for public keys.";
  }

  identity private-key-format {
    description
      "Base key-format identity for private keys.";
  }

  /****************************************************/
  /*   Identities for Private Key Format Structures   */
  /****************************************************/

  identity rsa-private-key-format {
    base private-key-format;
    description
      "Indicates that the private key value is encoded
       as an RSAPrivateKey (from RFC 3447).";
    reference
      "RFC 3447: PKCS #1: RSA Cryptography
                 Specifications Version 2.2";
  }

  identity ec-private-key-format {
    base private-key-format;
    description
      "Indicates that the private key value is encoded
       as an ECPrivateKey (from RFC 5915)";
    reference
      "RFC 5915: Elliptic Curve Private Key Structure";
  }

  identity one-asymmetric-key-format {
    if-feature "one-asymmetric-key-format";
    base private-key-format;
    description
      "Indicates that the private key value is a CMS
       OneAsymmetricKey structure, as defined in RFC 5958,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 5958: Asymmetric Key Packages
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /***************************************************/
  /*   Identities for Public Key Format Structures   */
  /***************************************************/

  identity ssh-public-key-format {
    base public-key-format;
    description
      "Indicates that the public key value is an SSH public key,
       as specified by RFC 4253, Section 6.6, i.e.:

         string    certificate or public key format
                   identifier
         byte[n]   key/certificate data.";
    reference
      "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
  }

  identity subject-public-key-info-format {
    base public-key-format;
    description
      "Indicates that the public key value is a SubjectPublicKeyInfo
       structure, as described in RFC 5280 encoded using ASN.1
       distinguished encoding rules (DER), as specified in
       ITU-T X.690.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /******************************************************/
  /*   Identities for Symmetric Key Format Structures   */
  /******************************************************/

  identity octet-string-key-format {
    base symmetric-key-format;
    description
      "Indicates that the key is encoded as a raw octet string.
       The length of the octet string MUST be appropriate for
       the associated algorithm's block size.

       How the associated algorithm is known is outside the
       scope of this module.  This statement also applies when
       the octet string has been encrypted.";
  }

  identity one-symmetric-key-format {
    if-feature "one-symmetric-key-format";
    base symmetric-key-format;
    description
      "Indicates that the private key value is a CMS
       OneSymmetricKey structure, as defined in RFC 6031,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 6031: Cryptographic Message Syntax (CMS)
                 Symmetric Key Package Content Type
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /*************************************************/
  /*   Identities for Encrypted Value Structures   */
  /*************************************************/

  identity encrypted-value-format {
    description
      "Base format identity for encrypted values.";
  }

  identity symmetrically-encrypted-value-format {
    if-feature "symmetrically-encrypted-value-format";
    base encrypted-value-format;
    description
      "Base format identity for symmetrically encrypted
       values.";
  }

  identity asymmetrically-encrypted-value-format {
    if-feature "asymmetrically-encrypted-value-format";
    base encrypted-value-format;
    description
      "Base format identity for asymmetrically encrypted
       values.";
  }

  identity cms-encrypted-data-format {
    if-feature "cms-encrypted-data-format";
    base symmetrically-encrypted-value-format;
    description
      "Indicates that the encrypted value conforms to
       the 'encrypted-data-cms' type with the constraint
       that the 'unprotectedAttrs' value is not set.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  identity cms-enveloped-data-format {
    if-feature "cms-enveloped-data-format";
    base asymmetrically-encrypted-value-format;
    description
      "Indicates that the encrypted value conforms to the
       'enveloped-data-cms' type with the following constraints:

       The EnvelopedData structure MUST have exactly one
       'RecipientInfo'.

       If the asymmetric key supports public key cryptography
       (e.g., RSA), then the 'RecipientInfo' must be a
       'KeyTransRecipientInfo' with the 'RecipientIdentifier'
       using a 'subjectKeyIdentifier' with the value set using
       'method 1' in RFC 7093 over the recipient's public key.

       Otherwise, if the asymmetric key supports key agreement
       (e.g., ECC), then the 'RecipientInfo' must be a
       'KeyAgreeRecipientInfo'.  The 'OriginatorIdentifierOrKey'
       value must use the 'OriginatorPublicKey' alternative.
       The 'UserKeyingMaterial' value must not be present.
       There must be exactly one 'RecipientEncryptedKeys' value
       having the 'KeyAgreeRecipientIdentifier' set to 'rKeyId'
       with the value set using 'method 1' in RFC 7093 over the
       recipient's public key.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)
       RFC 7093:
         Additional Methods for Generating Key
         Identifiers Values
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /***************************************************/
  /*   Typedefs for ASN.1 structures from RFC 2986   */
  /***************************************************/

  typedef csr-info {
    type binary;
    description
      "A CertificationRequestInfo structure, as defined in
       RFC 2986, encoded using ASN.1 distinguished encoding
       rules (DER), as specified in ITU-T X.690.";
    reference
      "RFC 2986: PKCS #10: Certification Request Syntax
                 Specification Version 1.7
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  typedef csr {
    type binary;
    description
      "A CertificationRequest structure, as specified in
       RFC 2986, encoded using ASN.1 distinguished encoding
       rules (DER), as specified in ITU-T X.690.";
    reference
      "RFC 2986:
         PKCS #10: Certification Request Syntax Specification
         Version 1.7
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /***************************************************/
  /*   Typedefs for ASN.1 structures from RFC 5280   */
  /***************************************************/

  typedef x509 {
    type binary;
    description
      "A Certificate structure, as specified in RFC 5280,
       encoded using ASN.1 distinguished encoding rules (DER),
       as specified in ITU-T X.690.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  typedef crl {
    type binary;
    description
      "A CertificateList structure, as specified in RFC 5280,
       encoded using ASN.1 distinguished encoding rules (DER),
       as specified in ITU-T X.690.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /***************************************************/
  /*   Typedefs for ASN.1 structures from RFC 6960   */
  /***************************************************/

  typedef oscp-request {
    type binary;
    description
      "A OCSPRequest structure, as specified in RFC 6960,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 6960:
         X.509 Internet Public Key Infrastructure Online
         Certificate Status Protocol - OCSP
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  typedef oscp-response {
    type binary;
    description
      "A OCSPResponse structure, as specified in RFC 6960,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 6960:
         X.509 Internet Public Key Infrastructure Online
         Certificate Status Protocol - OCSP
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  /***********************************************/
  /*   Typedefs for ASN.1 structures from 5652   */
  /***********************************************/

  typedef cms {
    type binary;
    description
      "A ContentInfo structure, as specified in RFC 5652,
       encoded using ASN.1 distinguished encoding rules (DER),
       as specified in ITU-T X.690.";
    reference
      "RFC 5652:
         Cryptographic Message Syntax (CMS)
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER).";
  }

  typedef data-content-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       data content type, as described by Section 4 in RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef signed-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       signed-data content type, as described by Section 5 in
       RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef enveloped-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       enveloped-data content type, as described by Section 6
       in RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef digested-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       digested-data content type, as described by Section 7
       in RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef encrypted-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       encrypted-data content type, as described by Section 8
       in RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef authenticated-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       authenticated-data content type, as described by Section 9
       in RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  /*********************************************************/
  /*   Typedefs for ASN.1 structures related to RFC 5280   */
  /*********************************************************/

  typedef trust-anchor-cert-x509 {
    type x509;
    description
      "A Certificate structure that MUST encode a self-signed
       root certificate.";
  }

  typedef end-entity-cert-x509 {
    type x509;
    description
      "A Certificate structure that MUST encode a certificate
       that is neither self-signed nor having Basic constraint
       CA true.";
  }

  /*********************************************************/
  /*   Typedefs for ASN.1 structures related to RFC 5652   */
  /*********************************************************/

  typedef trust-anchor-cert-cms {
    type signed-data-cms;
    description
      "A CMS SignedData structure that MUST contain the chain of
       X.509 certificates needed to authenticate the certificate
       presented by a client or end-entity.

       The CMS MUST contain only a single chain of certificates.
       The client or end-entity certificate MUST only authenticate
       to last intermediate CA certificate listed in the chain.

       In all cases, the chain MUST include a self-signed root
       certificate.  In the case where the root certificate is
       itself the issuer of the client or end-entity certificate,
       only one certificate is present.

       This CMS structure MAY (as applicable where this type is
       used) also contain suitably fresh (as defined by local
       policy) revocation objects with which the device can
       verify the revocation status of the certificates.

       This CMS encodes the degenerate form of the SignedData
       structure that is commonly used to disseminate X.509
       certificates and revocation objects (RFC 5280).";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile.";
  }

  typedef end-entity-cert-cms {
    type signed-data-cms;
    description
      "A CMS SignedData structure that MUST contain the end
       entity certificate itself, and MAY contain any number
       of intermediate certificates leading up to a trust
       anchor certificate.  The trust anchor certificate
       MAY be included as well.

       The CMS MUST contain a single end entity certificate.
       The CMS MUST NOT contain any spurious certificates.

       This CMS structure MAY (as applicable where this type is
       used) also contain suitably fresh (as defined by local
       policy) revocation objects with which the device can
       verify the revocation status of the certificates.

       This CMS encodes the degenerate form of the SignedData
       structure that is commonly used to disseminate X.509
       certificates and revocation objects (RFC 5280).";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile.";
  }

  /*****************/
  /*   Groupings   */
  /*****************/

  grouping encrypted-value-grouping {
    description
      "A reusable grouping for a value that has been encrypted by
       a referenced symmetric or asymmetric key.";
    container encrypted-by {
      nacm:default-deny-write;
      description
        "An empty container enabling a reference to the key that
         encrypted the value to be augmented in.  The referenced
         key MUST be a symmetric key or an asymmetric key.

         A symmetric key MUST be referenced via a leaf node called
         'symmetric-key-ref'.  An asymmetric key MUST be referenced
         via a leaf node called 'asymmetric-key-ref'.

         The leaf nodes MUST be direct descendants in the data tree,
         and MAY be direct descendants in the schema tree.";
    }
    leaf encrypted-value-format {
      type identityref {
        base encrypted-value-format;
      }
      mandatory true;
      description
        "Identifies the format of the 'encrypted-value' leaf.

         If 'encrypted-by' points to a symmetric key, then a
         'symmetrically-encrypted-value-format' based identity
         MUST by set (e.g., cms-encrypted-data-format).

         If 'encrypted-by' points to an asymmetric key, then an
         'asymmetrically-encrypted-value-format' based identity
         MUST by set (e.g., cms-enveloped-data-format).";
    }
    leaf encrypted-value {
      nacm:default-deny-write;
      type binary;
      must '../encrypted-by';
      mandatory true;
      description
        "The value, encrypted using the referenced symmetric
         or asymmetric key.  The value MUST be encoded using
         the format associated with the 'encrypted-value-format'
         leaf.";
    }
  }

  grouping password-grouping {
    description
      "A password that MAY be encrypted.";
    choice password-type {
      nacm:default-deny-write;
      mandatory true;
      description
        "Choice between password types.";
      case cleartext-password {
        leaf cleartext-password {
          nacm:default-deny-all;
          type string;
          description
            "The cleartext value of the password.";
        }
      }
      case encrypted-password {
        if-feature "password-encryption";
        container encrypted-password {
          description
            "A container for the encrypted password value.";
          uses encrypted-value-grouping;
        }
      }
    }
  }

  grouping symmetric-key-grouping {
    description
      "A symmetric key.";
    leaf key-format {
      nacm:default-deny-write;
      type identityref {
        base symmetric-key-format;
      }
      description
        "Identifies the symmetric key's format.  Implementations
         SHOULD ensure that the incoming symmetric key value is
         encoded in the specified format.

         For encrypted keys, the value is the same as it would
         have been if the key were not encrypted.";
    }
    choice key-type {
      nacm:default-deny-write;
      mandatory true;
      description
        "Choice between key types.";
      case cleartext-key {
        leaf cleartext-key {
          nacm:default-deny-all;
          type binary;
          must '../key-format';
          description
            "The binary value of the key.  The interpretation of
             the value is defined by the 'key-format' field.";
        }
      }
      case hidden-key {
        if-feature "hidden-keys";
        leaf hidden-key {
          type empty;
          must 'not(../key-format)';
          description
            "A hidden key.  How such keys are created is outside
             the scope of this module.";
        }
      }
      case encrypted-key {
        if-feature "symmetric-key-encryption";
        container encrypted-key {
          must '../key-format';
          description
            "A container for the encrypted symmetric key value.
             The interpretation of the 'encrypted-value' node
             is via the 'key-format' node";
          uses encrypted-value-grouping;
        }
      }
    }
  }

  grouping public-key-grouping {
    description
      "A public key.";
    leaf public-key-format {
      nacm:default-deny-write;
      type identityref {
        base public-key-format;
      }
      mandatory true;
      description
        "Identifies the public key's format. Implementations SHOULD
         ensure that the incoming public key value is encoded in the
         specified format.";
    }
    leaf public-key {
      nacm:default-deny-write;
      type binary;
      mandatory true;
      description
        "The binary value of the public key.  The interpretation
         of the value is defined by 'public-key-format' field.";
    }
  }

  grouping asymmetric-key-pair-grouping {
    description
      "A private key and its associated public key.  Implementations
       SHOULD ensure that the two keys are a matching pair.";
    uses public-key-grouping;
    leaf private-key-format {
      nacm:default-deny-write;
      type identityref {
        base private-key-format;
      }
      description
        "Identifies the private key's format.  Implementations SHOULD
         ensure that the incoming private key value is encoded in the
         specified format.

         For encrypted keys, the value is the same as it would have
         been if the key were not encrypted.";
    }
    choice private-key-type {
      nacm:default-deny-write;
      mandatory true;
      description
        "Choice between key types.";
      case cleartext-private-key {
        leaf cleartext-private-key {
          nacm:default-deny-all;
          type binary;
          must '../private-key-format';
          description
            "The value of the binary key  The key's value is
             interpreted by the 'private-key-format' field.";
        }
      }
      case hidden-private-key {
        if-feature "hidden-keys";
        leaf hidden-private-key {
          type empty;
          must 'not(../private-key-format)';
          description
            "A hidden key.  How such keys are created is
             outside the scope of this module.";
        }
      }
      case encrypted-private-key {
        if-feature "private-key-encryption";
        container encrypted-private-key {
          must '../private-key-format';
          description
            "A container for the encrypted asymmetric private key
             value.  The interpretation of the 'encrypted-value'
             node is via the 'private-key-format' node";
          uses encrypted-value-grouping;
        }
      }
    }
  }

  grouping certificate-expiration-grouping {
    description
      "A notification for when a certificate is about to, or
       already has, expired.";
    notification certificate-expiration {
      if-feature "certificate-expiration-notification";
      description
        "A notification indicating that the configured certificate
         is either about to expire or has already expired.  When to
         send notifications is an implementation specific decision,
         but it is RECOMMENDED that a notification be sent once a
         month for 3 months, then once a week for four weeks, and
         then once a day thereafter until the issue is resolved.";
      leaf expiration-date {
        type yang:date-and-time;
        mandatory true;
        description
          "Identifies the expiration date on the certificate.";
      }
    }
  }

  grouping trust-anchor-cert-grouping {
    description
      "A trust anchor certificate, and a notification for when
       it is about to (or already has) expire.";
    leaf cert-data {
      nacm:default-deny-write;
      type trust-anchor-cert-cms;
      description
        "The binary certificate data for this certificate.";
    }
    uses certificate-expiration-grouping;
  }

  grouping end-entity-cert-grouping {
    description
      "An end entity certificate, and a notification for when
       it is about to (or already has) expire.  Implementations
       SHOULD assert that, where used, the end entity certificate
       contains the expected public key.";
    leaf cert-data {
      nacm:default-deny-write;
      type end-entity-cert-cms;
      description
        "The binary certificate data for this certificate.";
    }
    uses certificate-expiration-grouping;
  }

  grouping generate-csr-grouping {
    description
      "Defines the 'generate-certificate-signing-request' action.";
    action generate-certificate-signing-request {
      if-feature "certificate-signing-request-generation";
      nacm:default-deny-all;
      description
        "Generates a certificate signing request structure for
         the associated asymmetric key using the passed subject
         and attribute values.

         This action statement is only available when the
         associated 'public-key-format' node's value is
         'subject-public-key-info-format'.";
      reference
        "RFC 6125:
          Representation and Verification of Domain-Based
          Application Service Identity within Internet Public Key
          Infrastructure Using X.509 (PKIX) Certificates in the
          Context of Transport Layer Security (TLS)";
      input {
        leaf csr-info {
          type ct:csr-info;
          mandatory true;
          description
            "A CertificationRequestInfo structure, as defined in
             RFC 2986.

             Enables the client to provide a fully-populated
             CertificationRequestInfo structure that the server
             only needs to sign in order to generate the complete
             'CertificationRequest' structure to return in the
             'output'.

             The 'AlgorithmIdentifier' field contained inside
             the 'SubjectPublicKeyInfo' field MUST be one known
             to be supported by the device.";
          reference
            "RFC 2986:
               PKCS #10: Certification Request Syntax Specification
             RFC AAAA:
               YANG Data Types and Groupings for Cryptography";
        }
      }
      output {
        leaf certificate-signing-request {
          type ct:csr;
          mandatory true;
          description
            "A CertificationRequest structure, as defined in
             RFC 2986.";
          reference
            "RFC 2986:
               PKCS #10: Certification Request Syntax Specification
             RFC AAAA:
               YANG Data Types and Groupings for Cryptography";
        }
      }
    }
  } // generate-csr-grouping

  grouping asymmetric-key-pair-with-cert-grouping {
    description
      "A private/public key pair and an associated certificate.
       Implementations SHOULD assert that certificates contain
       the matching public key.";
    uses asymmetric-key-pair-grouping;
    uses end-entity-cert-grouping;
    uses generate-csr-grouping;
  } // asymmetric-key-pair-with-cert-grouping

  grouping asymmetric-key-pair-with-certs-grouping {
    description
      "A private/public key pair and associated certificates.
       Implementations SHOULD assert that certificates contain
       the matching public key.";
    uses asymmetric-key-pair-grouping;
    container certificates {
      nacm:default-deny-write;
      description
        "Certificates associated with this asymmetric key.";
      list certificate {
        key "name";
        description
          "A certificate for this asymmetric key.";
        leaf name {
          type string;
          description
            "An arbitrary name for the certificate.";
        }
        uses end-entity-cert-grouping {
          refine "cert-data" {
            mandatory true;
          }
        }
      }
    }
    uses generate-csr-grouping;
  } // asymmetric-key-pair-with-certs-grouping

}

<CODE ENDS>

3. Security Considerations

3.1. No Support for CRMF

This document uses PKCS #10 [RFC2986] for the "generate-certificate-signing-request" action. The use of Certificate Request Message Format (CRMF) [RFC4211] was considered, but it was unclear if there was market demand for it. If it is desired to support CRMF in the future, a backwards compatible solution can be defined at that time.

3.2. No Support for Key Generation

Early revisions of this document included "rpc" statements for generating symmetric and asymmetric keys. These statements were removed due to an inability to obtain consensus for how to identify the key-algorithm to use. Thusly, the solution presented in this document only supports keys to be configured via an external client, which does not support Security best practice.

3.3. Unconstrained Public Key Usage

This module defines the "public-key-grouping" grouping, which enables the configuration of public keys without constraints on their usage, e.g., what operations the key is allowed to be used for (encryption, verification, both).

The "asymmetric-key-pair-grouping" grouping uses the aforementioned "public-key-grouping" grouping, and carries the same traits.

The "asymmetric-key-pair-with-cert-grouping" grouping uses the aforementioned "asymmetric-key-pair-grouping" grouping, whereby each certificate may constrain the usage of the public key according to local policy.

3.4. Unconstrained Private Key Usage

This module defines the "asymmetric-key-pair-grouping" grouping, which enables the configuration of private keys without constraints on their usage, e.g., what operations the key is allowed to be used for (e.g., signature, decryption, both).

The "asymmetric-key-pair-with-cert-grouping" uses the aforementioned "asymmetric-key-pair-grouping" grouping, whereby configured certificates (e.g., identity certificates) may constrain the use of the public key according to local policy.

3.5. Strength of Keys Conveyed

When accessing key values, it is desireable that implementations ensure that the strength of the keys being accessed is not greater than the strength of the underlying secure transport connection over which the keys are conveyed. However, comparing key strengths can be complicated and difficult to implement in practice.

That said, expert Security opinion suggests that already it is infeasible to break a 128-bit symmetric key using a classical computer, and thus the concern for conveying higher-strength keys begins to lose its allure.

Implementations SHOULD only use secure transport protocols meeting local policy. A reasonable policy may, e.g., state that only ciphersuites listed as "recommended" by the IETF be used (e.g., [RFC7525] for TLS).

3.6. Encrypting Passwords

The module contained within this document enables passwords to be encrypted. Passwords may be encrypted via a symmetric key using the "cms-encrypted-data-format" format. This format uses the CMS EncryptedData structure, which allows any encryption algorithm to be used.

In order to thwart rainbow attacks, algorithms that result in a unique output for the same input SHOULD NOT be used. For instance, AES using "ECB" SHOULD NOT be used to encrypt passwords, whereas "CBC" mode is permissible since an unpredictable initialization vector (IV) MUST be used for each use.

3.7. Deletion of Cleartext Key Values

This module defines storage for cleartext key values that SHOULD be zeroized when deleted, so as to prevent the remnants of their persisted storage locations from being analyzed in any meaningful way.

The cleartext key values are the "cleartext-key" node defined in the "symmetric-key-grouping" grouping (Section 2.1.4.3) and the "cleartext-private-key" node defined in the "asymmetric-key-pair-grouping" grouping ("Section 2.1.4.5).

3.8. The "ietf-crypto-types" YANG Module

The YANG module in this document defines "grouping" statements that are designed to be accessed via YANG based management protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols have mandatory-to-implement secure transport layers (e.g., SSH, TLS) with mutual authentication.

The NETCONF access control model (NACM) [RFC8341] provides the means to restrict access for particular users to a pre-configured subset of all available protocol operations and content.

Since the module in this document only defines groupings, these considerations are primarily for the designers of other modules that use these groupings.

Some of the readable data nodes defined in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability:

All the writable data nodes defined by all the groupings defined in this module may be considered sensitive or vulnerable in some network environments. For instance, even the modification of a public key or a certificate can dramatically alter the implemented security policy. For this reason, the NACM extension "default-deny-write" has been applied to all the data nodes defined in the module.

Some of the operations in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control access to these operations. These are the operations and their sensitivity/vulnerability:

4. IANA Considerations

4.1. The "IETF XML" Registry

This document registers one URI in the "ns" subregistry of the "IETF XML" registry [RFC3688]. Following the format in [RFC3688], the following registration is requested:

   URI: urn:ietf:params:xml:ns:yang:ietf-crypto-types
   Registrant Contact: The IESG
   XML: N/A, the requested URI is an XML namespace.

4.2. The "YANG Module Names" Registry

This document registers one YANG module in the "YANG Module Names" registry [RFC6020]. Following the format in [RFC6020], the following registration is requested:

   name:         ietf-crypto-types
   namespace:    urn:ietf:params:xml:ns:yang:ietf-crypto-types
   prefix:       ct
   reference:    RFC AAAA

5. References

5.1. Normative References

[ITU.X680.2015]
International Telecommunication Union, "Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITU-T Recommendation X.680, ISO/IEC 8824-1:2015, , <https://www.itu.int/rec/T-REC-X.680/>.
[ITU.X690.2015]
International Telecommunication Union, "Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1:2015, , <https://www.itu.int/rec/T-REC-X.690/>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC3447]
Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, DOI 10.17487/RFC3447, , <https://www.rfc-editor.org/info/rfc3447>.
[RFC4253]
Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, , <https://www.rfc-editor.org/info/rfc4253>.
[RFC5280]
Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, , <https://www.rfc-editor.org/info/rfc5280>.
[RFC5652]
Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, , <https://www.rfc-editor.org/info/rfc5652>.
[RFC5958]
Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, , <https://www.rfc-editor.org/info/rfc5958>.
[RFC6031]
Turner, S. and R. Housley, "Cryptographic Message Syntax (CMS) Symmetric Key Package Content Type", RFC 6031, DOI 10.17487/RFC6031, , <https://www.rfc-editor.org/info/rfc6031>.
[RFC6991]
Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://www.rfc-editor.org/info/rfc6991>.
[RFC7093]
Turner, S., Kent, S., and J. Manger, "Additional Methods for Generating Key Identifiers Values", RFC 7093, DOI 10.17487/RFC7093, , <https://www.rfc-editor.org/info/rfc7093>.
[RFC7950]
Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, , <https://www.rfc-editor.org/info/rfc7950>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8341]
Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/info/rfc8341>.

5.2. Informative References

[I-D.ietf-netconf-crypto-types]
Watsen, K., "YANG Data Types and Groupings for Cryptography", Work in Progress, Internet-Draft, draft-ietf-netconf-crypto-types-22, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-crypto-types-22>.
[I-D.ietf-netconf-http-client-server]
Watsen, K., "YANG Groupings for HTTP Clients and HTTP Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-http-client-server-09, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-http-client-server-09>.
[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore", Work in Progress, Internet-Draft, draft-ietf-netconf-keystore-24, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-keystore-24>.
[I-D.ietf-netconf-netconf-client-server]
Watsen, K., "NETCONF Client and Server Models", Work in Progress, Internet-Draft, draft-ietf-netconf-netconf-client-server-25, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-netconf-client-server-25>.
[I-D.ietf-netconf-restconf-client-server]
Watsen, K., "RESTCONF Client and Server Models", Work in Progress, Internet-Draft, draft-ietf-netconf-restconf-client-server-25, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-restconf-client-server-25>.
[I-D.ietf-netconf-ssh-client-server]
Watsen, K., "YANG Groupings for SSH Clients and SSH Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-ssh-client-server-27, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-ssh-client-server-27>.
[I-D.ietf-netconf-tcp-client-server]
Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients and TCP Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-tcp-client-server-12, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-tcp-client-server-12>.
[I-D.ietf-netconf-tls-client-server]
Watsen, K., "YANG Groupings for TLS Clients and TLS Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-tls-client-server-27, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-tls-client-server-27>.
[I-D.ietf-netconf-trust-anchors]
Watsen, K., "A YANG Data Model for a Truststore", Work in Progress, Internet-Draft, draft-ietf-netconf-trust-anchors-17, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-trust-anchors-17>.
[RFC2986]
Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, DOI 10.17487/RFC2986, , <https://www.rfc-editor.org/info/rfc2986>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/info/rfc3688>.
[RFC4211]
Schaad, J., "Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)", RFC 4211, DOI 10.17487/RFC4211, , <https://www.rfc-editor.org/info/rfc4211>.
[RFC5056]
Williams, N., "On the Use of Channel Bindings to Secure Channels", RFC 5056, DOI 10.17487/RFC5056, , <https://www.rfc-editor.org/info/rfc5056>.
[RFC5915]
Turner, S. and D. Brown, "Elliptic Curve Private Key Structure", RFC 5915, DOI 10.17487/RFC5915, , <https://www.rfc-editor.org/info/rfc5915>.
[RFC6020]
Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://www.rfc-editor.org/info/rfc6020>.
[RFC6125]
Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, , <https://www.rfc-editor.org/info/rfc6125>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
[RFC7525]
Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, , <https://www.rfc-editor.org/info/rfc7525>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/info/rfc8040>.
[RFC8340]
Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <https://www.rfc-editor.org/info/rfc8340>.
[RFC8342]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, , <https://www.rfc-editor.org/info/rfc8342>.

Appendix A. Change Log

This section is to be removed before publishing as an RFC.

A.1. I-D to 00

  • Removed groupings and notifications.
  • Added typedefs for identityrefs.
  • Added typedefs for other RFC 5280 structures.
  • Added typedefs for other RFC 5652 structures.
  • Added convenience typedefs for RFC 4253, RFC 5280, and RFC 5652.

A.2. 00 to 01

  • Moved groupings from the draft-ietf-netconf-keystore here.

A.3. 01 to 02

  • Removed unwanted "mandatory" and "must" statements.
  • Added many new crypto algorithms (thanks Haiguang!)
  • Clarified in asymmetric-key-pair-with-certs-grouping, in certificates/certificate/name/description, that if the name MUST NOT match the name of a certificate that exists independently in <operational>, enabling certs installed by the manufacturer (e.g., an IDevID).

A.4. 02 to 03

  • renamed base identity 'asymmetric-key-encryption-algorithm' to 'asymmetric-key-algorithm'.
  • added new 'asymmetric-key-algorithm' identities for secp192r1, secp224r1, secp256r1, secp384r1, and secp521r1.
  • removed 'mac-algorithm' identities for mac-aes-128-ccm, mac-aes-192-ccm, mac-aes-256-ccm, mac-aes-128-gcm, mac-aes-192-gcm, mac-aes-256-gcm, and mac-chacha20-poly1305.
  • for all -cbc and -ctr identities, renamed base identity 'symmetric-key-encryption-algorithm' to 'encryption-algorithm'.
  • for all -ccm and -gcm identities, renamed base identity 'symmetric-key-encryption-algorithm' to 'encryption-and-mac-algorithm' and renamed the identity to remove the "enc-" prefix.
  • for all the 'signature-algorithm' based identities, renamed from 'rsa-*' to 'rsassa-*'.
  • removed all of the "x509v3-" prefixed 'signature-algorithm' based identities.
  • added 'key-exchange-algorithm' based identities for 'rsaes-oaep' and 'rsaes-pkcs1-v1_5'.
  • renamed typedef 'symmetric-key-encryption-algorithm-ref' to 'symmetric-key-algorithm-ref'.
  • renamed typedef 'asymmetric-key-encryption-algorithm-ref' to 'asymmetric-key-algorithm-ref'.
  • added typedef 'encryption-and-mac-algorithm-ref'.
  • Updated copyright date, boilerplate template, affiliation, and folding algorithm.

A.5. 03 to 04

  • ran YANG module through formatter.

A.6. 04 to 05

  • fixed broken symlink causing reformatted YANG module to not show.

A.7. 05 to 06

  • Added NACM annotations.
  • Updated Security Considerations section.
  • Added 'asymmetric-key-pair-with-cert-grouping' grouping.
  • Removed text from 'permanently-hidden' enum regarding such keys not being backed up or restored.
  • Updated the boilerplate text in module-level "description" statement to match copyeditor convention.
  • Added an explanation to the 'public-key-grouping' and 'asymmetric-key-pair-grouping' statements as for why the nodes are not mandatory (e.g., because they may exist only in <operational>.
  • Added 'must' expressions to the 'public-key-grouping' and 'asymmetric-key-pair-grouping' statements ensuring sibling nodes are either all exist or do not all exist.
  • Added an explanation to the 'permanently-hidden' that the value cannot be configured directly by clients and servers MUST fail any attempt to do so.
  • Added 'trust-anchor-certs-grouping' and 'end-entity-certs-grouping' (the plural form of existing groupings).
  • Now states that keys created in <operational> by the *-hidden-key actions are bound to the lifetime of the parent 'config true' node, and that subsequent invocations of either action results in a failure.

A.8. 06 to 07

  • Added clarifications that implementations SHOULD assert that configured certificates contain the matching public key.
  • Replaced the 'generate-hidden-key' and 'install-hidden-key' actions with special 'crypt-hash' -like input/output values.

A.9. 07 to 08

  • Removed the 'generate-key and 'hidden-key' features.
  • Added grouping symmetric-key-grouping
  • Modified 'asymmetric-key-pair-grouping' to have a 'choice' statement for the keystone module to augment into, as well as replacing the 'union' with leafs (having different NACM settings.

A.10. 08 to 09

  • Converting algorithm from identities to enumerations.

A.11. 09 to 10

  • All the below changes are to the algorithm enumerations defined in ietf-crypto-types.
  • Add in support for key exchange over x.25519 and x.448 based on RFC 8418.
  • Add in SHAKE-128, SHAKE-224, SHAKE-256, SHAKE-384 and SHAKE 512
  • Revise/add in enum of signature algorithm for x25519 and x448
  • Add in des3-cbc-sha1 for IPSec
  • Add in sha1-des3-kd for IPSec
  • Add in definit for rc4-hmac and rc4-hmac-exp. These two algorithms have been deprecated in RFC 8429. But some existing draft in i2nsf may still want to use them.
  • Add x25519 and x448 curve for asymmetric algorithms
  • Add signature algorithms ed25519, ed25519-cts, ed25519ph
  • add signature algorithms ed448, ed448ph
  • Add in rsa-sha2-256 and rsa-sha2-512 for SSH protocols (rfc8332)

A.12. 10 to 11

  • Added a "key-format" identity.
  • Added symmetric keys to the example in Section 2.2.

A.13. 11 to 12

  • Removed all non-essential (to NC/RC) algorithm types.
  • Moved remaining algorithm types each into its own module.
  • Added a 'config false' "algorithms-supported" list to each of the algorithm-type modules.

A.14. 12 to 13

  • Added the four features: "[encrypted-]one-[a]symmetric-key-format", each protecting a 'key-format' identity of the same name.
  • Added 'must' expressions asserting that the 'key-format' leaf exists whenever a non-hidden key is specified.
  • Improved the 'description' statements and added 'reference' statements for the 'key-format' identities.
  • Added a questionable forward reference to "encrypted-*" leafs in a couple 'when' expressions.
  • Did NOT move "config false" alg-supported lists to SSH/TLS drafts.

A.15. 13 to 14

  • Resolved the "FIXME: forward ref" issue by modulating 'must', 'when', and 'mandatory' expressions.
  • Moved the 'generatesymmetric-key' and 'generate-asymmetric-key' actions from ietf-keystore to ietf-crypto-types, now as RPCs.
  • Cleaned up various description statements and removed lingering FIXMEs.
  • Converted the "iana-<alg-type>-algs" YANG modules to IANA registries with instructions for how to generate modules from the registries, whenever they may be updated.

A.16. 14 to 15

  • Removed the IANA-maintained registries for symmetric, asymmetric, and hash algorithms.
  • Removed the "generate-symmetric-key" and "generate-asymmetric-key" RPCs.
  • Removed the "algorithm" node in the various symmetric and asymmetric key groupings.
  • Added 'typedef csr' and 'feature certificate-signing-request-generation'.
  • Refined a usage of "end-entity-cert-grouping" to make the "cert" node mandatory true.
  • Added a "Note to Reviewers" note to first page.

A.17. 15 to 16

  • Updated draft title (refer to "Groupings" too).
  • Removed 'end-entity-certs-grouping' as it wasn't being used anywhere.
  • Removed 'trust-anchor-certs-grouping' as it was no longer being used after modifying 'local-or-truststore-certs-grouping' to use lists (not leaf-lists).
  • Renamed "cert" to "cert-data" in trust-anchor-cert-grouping.
  • Added "csr-info" typedef, to complement the existing "csr" typedef.
  • Added "ocsp-request" and "ocsp-response" typedefs, to complement the existing "crl" typedef.
  • Added "encrypted" cases to both symmetric-key-grouping and asymmetric-key-pair-grouping (Moved from Keystore draft).
  • Expanded "Data Model Overview section(s) [remove "wall" of tree diagrams].
  • Updated the Security Considerations section.

A.18. 16 to 17

  • [Re]-added a "Strength of Keys Configured" Security Consideration
  • Prefixed "cleartext-" in the "key" and "private-key" node names.

A.19. 17 to 18

  • Fixed issues found by the SecDir review of the "keystore" draft.
  • Added "password-grouping", discussed during the IETF 108 session.

A.20. 18 to 19

  • Added a "Unconstrained Public Key Usage" Security Consideration to address concern raised by SecDir of the 'truststore' draft.
  • Added a "Unconstrained Private Key Usage" Security Consideration to address concern raised by SecDir of the 'truststore' draft.
  • Changed the encryption strategy, after conferring with Russ Housley.
  • Added a "password-grouping" example to the "crypto-types-usage" example.
  • Added an "Encrypting Passwords" section to Security Consideration.
  • Addressed other comments raised by YANG Doctor.

A.21. 19 to 20

  • Nits found via YANG Doctors reviews.
  • Aligned modules with `pyang -f` formatting.

A.22. 20 to 21

  • Replaced "base64encodedvalue==" with "BASE64VALUE=".
  • Accommodated SecDir review by Valery Smyslov.

A.23. 21 to 22

  • fixup the 'WG Web' and 'WG List' lines in YANG module(s)
  • fixup copyright (i.e., s/Simplified/Revised/) in YANG module(s)
  • added 'hidden-keys' feature.

A.24. 22 to 23

  • Fixed an example to reference correct key.
  • Fixed an example to not have line-returns around the encoding for a binary value.

Acknowledgements

The authors would like to thank for following for lively discussions on list and in the halls (ordered by first name): Balazs Kovacs, Eric Voit, Juergen Schoenwaelder, Liang Xia, Martin Bjoerklund, Nick Hancock, Rich Salz, Rob Wilton, Russ Housley, Sandra Murphy, Tom Petch, Valery Smyslov, and Wang Haiguang.

Author's Address

Kent Watsen
Watsen Networks

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