Internet Engineering Task Force (IETF) P. Hoyer
Request for Comments: 6030 ActivIdentity
Category: Standards Track M. Pei
ISSN: 2070-1721 VeriSign
S. Machani
Diversinet
October 2010
Portable Symmetric Key Container (PSKC)
Abstract
This document specifies a symmetric key format for the transport and
provisioning of symmetric keys to different types of crypto modules.
For example, One-Time Password (OTP) shared secrets or symmetric
cryptographic keys to strong authentication devices. A standard key
transport format enables enterprises to deploy best-of-breed
solutions combining components from different vendors into the same
infrastructure.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6030.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................4
1.1. Key Words ..................................................4
1.2. Version Support ............................................4
1.3. Namespace Identifiers ......................................5
1.3.1. Defined Identifiers .................................5
1.3.2. Referenced Identifiers ..............................5
2. Terminology .....................................................6
3. Portable Key Container Entities Overview and Relationships ......6
4. <KeyContainer> Element: The Basics ..............................8
4.1. <Key>: Embedding Keying Material and Key-Related
Information ................................................8
4.2. Key Value Encoding ........................................10
4.2.1. AES Key Value Encoding .............................11
4.2.2. Triple-DES Key Value Encoding ......................11
4.3. Transmission of Supplementary Information .................12
4.3.1. <DeviceInfo> Element: Unique Device
Identification .....................................13
4.3.2. <CryptoModuleInfo> Element: CryptoModule
Identification .....................................15
4.3.3. <UserId> Element: User Identification ..............15
4.3.4. <AlgorithmParameters> Element:
Supplementary Information for OTP and CR Algorithms 15
4.4. Transmission of Key Derivation Values .....................17
5. Key Policy .....................................................19
5.1. PIN Algorithm Definition ..................................23
6. Key Protection Methods .........................................23
6.1. Encryption Based on Pre-Shared Keys .......................24
6.1.1. MAC Method .........................................26
6.2. Encryption Based on Passphrase-Based Keys .................27
6.3. Encryption Based on Asymmetric Keys .......................29
6.4. Padding of Encrypted Values for Non-Padded
Encryption Algorithms .....................................31
7. Digital Signature ..............................................31
8. Bulk Provisioning ..............................................33
9. Extensibility ..................................................35
10. PSKC Algorithm Profile ........................................36
10.1. HOTP .....................................................36
10.2. PIN ......................................................37
11. XML Schema ....................................................38
12. IANA Considerations ...........................................44
12.1. Content-Type Registration for 'application/pskc+xml' .....44
12.2. XML Schema Registration ..................................45
12.3. URN Sub-Namespace Registration ...........................46
12.4. PSKC Algorithm Profile Registry ..........................46
12.5. PSKC Version Registry ....................................47
12.6. Key Usage Registry .......................................47
13. Security Considerations .......................................48
13.1. PSKC Confidentiality .....................................49
13.2. PSKC Integrity ...........................................50
13.3. PSKC Authenticity ........................................50
14. Contributors ..................................................50
15. Acknowledgements ..............................................50
16. References ....................................................51
16.1. Normative References .....................................51
16.2. Informative References ...................................52
Appendix A. Use Cases ............................................54
A.1. Online Use Cases ..........................................54
A.1.1. Transport of Keys from Server to Cryptographic
Module ................................................54
A.1.2. Transport of Keys from Cryptographic Module to
Cryptographic Module ..................................54
A.1.3. Transport of Keys from Cryptographic Module to
Server ................................................55
A.1.4. Server-to-Server Bulk Import/Export of Keys ...........55
A.2. Offline Use Cases .........................................55
A.2.1. Server-to-Server Bulk Import/Export of Keys ...........55
Appendix B. Requirements .........................................56
1. Introduction
With the increasing use of symmetric-key-based systems, such as
encryption of data at rest or systems used for strong authentication,
such as those based on One-Time Password (OTP) and Challenge/Response
(CR) mechanisms, there is a need for vendor interoperability and a
standard format for importing and exporting (provisioning) symmetric
keys. For instance, traditionally, vendors of authentication servers
and service providers have used proprietary formats for importing and
exporting these keys into their systems, thus making it hard to use
tokens from two different vendors.
This document defines a standardized XML-based key container, called
Portable Symmetric Key Container (PSKC), for transporting symmetric
keys and key-related metadata. The document also specifies the
information elements that are required when the symmetric key is
utilized for specific purposes, such as the initial counter in the
HMAC-Based One-Time Password (HOTP) [HOTP] algorithm. It also
creates an IANA registry for algorithm profiles where algorithms,
their metadata and PSKC transmission profile can be recorded for a
centralized, standardized reference.
1.1. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Version Support
There is a provision made in the syntax for an explicit version
number. Only version "1.0" is currently specified.
The numbering scheme for PSKC versions is "<major>.<minor>". The
major and minor numbers MUST be treated as separate integers and each
number MAY be incremented higher than a single digit. Thus, "PSKC
2.4" would be a lower version than "PSKC 2.13", which in turn would
be lower than "PSKC 12.3". Leading zeros (e.g., "PSKC 6.01") MUST be
ignored by recipients and MUST NOT be sent.
The major version number should be incremented only if the message
format (e.g., element structure) has changed so dramatically that an
older version implementation would not be able to interoperate with a
newer version. The minor version number indicates new capabilities,
and it MUST be ignored by an entity with a smaller minor version
number but used for informational purposes by the entity with the
larger minor version number.
1.3. Namespace Identifiers
This document uses Uniform Resource Identifiers (URIs) [RFC3986] to
identify resources, algorithms, and semantics.
1.3.1. Defined Identifiers
The XML namespace [XMLNS] URI for Version 1.0 of PSKC is:
"urn:ietf:params:xml:ns:keyprov:pskc"
References to qualified elements in the PSKC schema defined in this
specification and used in the example use the prefix "pskc" (defined
as xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"). It is
RECOMMENDED to use this namespace in implementations.
1.3.2. Referenced Identifiers
The PSKC syntax presented in this document relies on algorithm
identifiers and elements defined in the XML Signature [XMLDSIG]
namespace:
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
References to the XML Signature namespace are represented by the
prefix "ds".
PSKC also relies on algorithm identifiers and elements defined in the
XML Encryption [XMLENC] namespace:
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
References to the XML Encryption namespace are represented by the
prefix "xenc".
When protecting keys in transport with passphrase-based keys, PSKC
also relies on the derived key element defined in the XML Encryption
Version 1.1 [XMLENC11] namespace:
xmlns:xenc11="http://www.w3.org/2009/xmlenc11#"
References to the XML Encryption Version 1.1 namespace are
represented by the prefix "xenc11".
When protecting keys in transport with passphrase-based keys, PSKC
also relies on algorithm identifiers and elements defined in the PKCS
#5 [PKCS5] namespace:
xmlns:pkcs5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
References to the PKCS #5 namespace are represented by the prefix
"pkcs5".
2. Terminology
NOTE: In subsequent sections of the document, we highlight
**mandatory** XML elements and attributes. Optional elements and
attributes are not explicitly indicated, i.e., if it does not say
mandatory, it is optional.
3. Portable Key Container Entities Overview and Relationships
The portable key container is based on an XML schema definition and
contains the following main conceptual entities:
1. KeyContainer entity - representing the container that carries a
number of KeyPackage entities. A valid container MUST carry at
least one KeyPackage entity.
2. KeyPackage entity - representing the package of at most one key
and its related provisioning endpoint or current usage endpoint,
such as a physical or virtual device and a specific CryptoModule.
3. DeviceInfo entity - representing the information about the device
and criteria to identify uniquely the device.
4. CryptoModuleInfo entity - representing the information about the
CryptoModule where the keys reside or to which they are
provisioned.
5. Key entity - representing the key transported or provisioned.
6. Data entity - representing a list of metadata related to the key,
where the element name is the name of the metadata and its
associated value is either in encrypted (for example, for <Data>
element <Secret>) or plaintext (for example, the <Data> element
<Counter>) form.
Figure 1 shows the high-level structure of the PSKC data elements.
-----------------
| KeyContainer |
|---------------|
| EncryptionKey |
| Signature |
| ... |
-----------------
|
|
/|\ 1..n
---------------- ----------------
| KeyPackage | 0..1| DeviceInfo |
|--------------|--------|--------------|
| |-- | SerialNo |
---------------- | | Manufacturer |
| | | .... |
| | ----------------
Notes:
Figure 1 mentions a DeviceInfo field called "SerialNumber" however it should be "SerialNo".
/|\ 0..1 |
---------------- | --------------------
| Key | | 0..1| CryptoModuleInfo |
|--------------| -----|------------------|
| Id | | Id |
| Algorithm | |.... |
| UserId | --------------------
| Policy |
| .... |
----------------
|
|
/|\ 0..n
--------------------------------------- - -
| | |
------------------ ---------------- -------- - -
| Data:Secret | | Data:Counter | | Data:other
|----------------| |--------------| |-- - -
| EncryptedValue | | PlainValue |
| ValueMAC | ----------------
------------------
Figure 1: PSKC Data Elements Relationship Diagram
The following sections describe in detail all the entities and
related XML schema elements and attributes.
4. <KeyContainer> Element: The Basics
In its most basic form, a PSKC document uses the top-level element
<KeyContainer> and a single <KeyPackage> element to carry key
information.
The following example shows a simple PSKC document. We will use it
to describe the structure of the <KeyContainer> element and its child
elements.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0"
Id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<KeyPackage>
<Key Id="12345678"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer-A</Issuer>
<Data>
<Secret>
<PlainValue>MTIzNA==
</PlainValue>
</Secret>
</Data>
</Key>
</KeyPackage>
</KeyContainer>
Figure 2: Basic PSKC Key Container Example
The attributes of the <KeyContainer> element have the following
semantics:
'Version': The 'Version' attribute is used to identify the version
of the PSKC schema version. This specification defines the
initial version ("1.0") of the PSKC schema. This attribute MUST
be included.
'Id': The 'Id' attribute carries a unique identifier for the
container. As such, it helps to identify a specific key container
in cases in which multiple containers are embedded in larger XML
documents.
4.1. <Key>: Embedding Keying Material and Key-Related Information
The following attributes of the <Key> element MUST be included at a
minimum:
'Id': This attribute carries a unique identifier for the symmetric
key in the context of key provisioning exchanges between two
parties. This means that if PSKC is used in multiple interactions
between a sending and receiving party, using different containers
referencing the same keys, the 'Id' attribute of <Key> MUST use
the same value (e.g., after initial provisioning, if a system
wants to update key metadata values in the other system, the value
of the 'Id' attribute of the <Key> where the metadata is to be
updated MUST be the same of the original 'Id' attribute value
provisioned). The identifier is defined as a string of
alphanumeric characters.
'Algorithm': This attribute contains a unique identifier for the
PSKC algorithm profile. This profile associates specific
semantics to the elements and attributes contained in the <Key>
element. This document describes profiles for open standards
algorithms in Section 10. Additional profiles are defined in the
following informative document: [PSKC-ALGORITHM-PROFILES].
The <Key> element has a number of optional child elements. An
initial set is described below:
<Issuer>: This element represents the name of the party that issued
the key. For example, a bank "Foobar Bank, Inc." issuing hardware
tokens to their retail banking users may set this element to
'Foobar Bank, Inc.'.
<FriendlyName>: A human-readable name for the secret key for easier
reference. This element serves informational purposes only. This
element is a language-dependent string; hence, it SHOULD have an
attribute xml:lang="xx" where xx is the language identifier as
specified in [RFC5646]. If no xml:lang attribute is present,
implementations MUST assume the language to be English as defined
by setting the attribute value to 'en' (e.g., xml:lang="en").
<AlgorithmParameters>: This element carries parameters that
influence the result of the algorithmic computation, for example,
response truncation and format in OTP and CR algorithms. A more
detailed discussion of the element can be found in Section 4.3.4.
<Data>: This element carries data about and related to the key. The
following child elements are defined for the <Data> element:
<Secret>: This element carries the value of the key itself in a
binary representation. Please see Section 4.2 for more details
on Key Value Encoding.
<Counter>: This element contains the event counter for event-
based OTP algorithms.
<Time>: This element contains the time for time-based OTP
algorithms. (If time intervals are used, this element carries
the number of time intervals passed from a specific start
point, normally it is algorithm dependent).
<TimeInterval>: This element carries the time interval value for
time-based OTP algorithms in seconds (a typical value for this
would be 30, indicating a time interval of 30 seconds).
<TimeDrift>: This element contains the device clock drift value
for time-based OTP algorithms. The integer value (positive or
negative drift) that indicates the number of time intervals
that a validation server has established the device clock
drifted after the last successful authentication. So, for
example, if the last successful authentication established a
device time value of 8 intervals from a specific start date but
the validation server determines the time value at 9 intervals,
the server SHOULD record the drift as -1.
All the elements listed above (and those defined in the future)
obey a simple structure in that they MUST support child elements
to convey the data value in either plaintext or encrypted format:
Plaintext: The <PlainValue> element carries a plaintext value
that is typed, for example, to xs:integer.
Encrypted: The <EncryptedValue> element carries an encrypted
value.
ValueMAC: The <ValueMAC> element is populated with a Message
Authentication Code (MAC) generated from the encrypted value in
case the encryption algorithm does not support integrity
checks. The example shown in Figure 2 illustrates the usage of
the <Data> element with two child elements, namely <Secret> and
<Counter>. Both elements carry a plaintext value within the
<PlainValue> child element.
4.2. Key Value Encoding
Two parties receiving the same key value OCTET STRING, resulting in
decoding the xs:base64Binary, inside the <PlainValue> or
<EncryptedValue> elements, must make use of the key in exactly the
same way in order to interoperate. To ensure that, it is necessary
to define a correspondence between the OCTET STRING and the notation
in the standard algorithm description that defines how the key is
used. The next sections establish that correspondence for the AES
algorithm [FIPS197] and the Triple Data Encryption Algorithm (TDEA or
Triple DES) [SP800-67]. Unless otherwise specified for a specific
algorithm, the OCTET STRING encoding MUST follow the AES Key Value
Encoding.
4.2.1. AES Key Value Encoding
[FIPS197], Section 5.2, titled "Key Expansion", uses the input key as
an array of bytes indexed starting at 0. The first octet of the
OCTET STRING SHALL become the key byte in the AES, labeled index 0 in
[FIPS197]; the succeeding octets of the OCTET STRING SHALL become key
bytes in AES, in increasing index order.
Proper parsing and key load of the contents of the OCTET STRING for
AES SHALL be determined by using the following value for the
<PlainValue> element (binaryBase64-encoded) to generate and match the
key expansion test vectors in [FIPS197], Appendix A, for AES
Cipher Key: 2b 7e 15 16 28 ae d2 a6 ab f7 15 88 09 cf 4f 3c
...
<PlainValue>K34VFiiu0qar9xWICc9PPA==</PlainValue>
...
4.2.2. Triple-DES Key Value Encoding
A Triple-DES key consists of three keys for the cryptographic engine
(Key1, Key2, and Key3) that are each 64 bits (56 key bits and 8
parity bits); the three keys are also collectively referred to as a
key bundle [SP800-67]. A key bundle may employ either two or three
independent keys. When only two independent keys are employed
(called two-key Triple DES), the same value is used for Key1 and
Key3.
Each key in a Triple-DES key bundle is expanded into a key schedule
according to a procedure defined in [SP800-67], Appendix A. That
procedure numbers the bits in the key from 1 to 64, with number 1
being the leftmost, or most significant bit (MSB). The first octet
of the OCTET STRING SHALL be bits 1 through 8 of Key1 with bit 1
being the MSB. The second octet of the OCTET STRING SHALL be bits 9
through 16 of Key1, and so forth, so that the trailing octet of the
OCTET STRING SHALL be bits 57 through 64 of Key3 (or Key2 for two-key
Triple DES).
Proper parsing and key load of the contents of the OCTET STRING for
Triple DES SHALL be determined by using the following <PlainValue>
element (binaryBase64-encoded) to generate and match the key
expansion test vectors in [SP800-67], Appendix B, for the key bundle:
Key1 = 0123456789ABCDEF
Key2 = 23456789ABCDEF01
Key3 = 456789ABCDEF0123
...
<PlainValue>ASNFZ4mrze8jRWeJq83vAUVniavN7wEj</PlainValue>
...
4.3. Transmission of Supplementary Information
A PSKC document can contain a number of additional information
regarding device identification, cryptographic module identification,
user identification, and parameters for usage with OTP and CR
algorithms. The following example, see Figure 3, is used as a
reference for the subsequent sub-sections.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0"
Id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<KeyPackage>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
<UserId>DC=example-bank,DC=net</UserId>
</DeviceInfo>
<CryptoModuleInfo>
<Id>CM_ID_001</Id>
</CryptoModuleInfo>
<Key Id="12345678"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<UserId>UID=jsmith,DC=example-bank,DC=net</UserId>
</Key>
</KeyPackage>
</KeyContainer>
Figure 3: PSKC Key Container Example with Supplementary Data
4.3.1. <DeviceInfo> Element: Unique Device Identification
The <DeviceInfo> element uniquely identifies the device to which the
<KeyPackage> is provisioned. Since devices can come in different
form factors, such as hardware tokens, smart-cards, soft tokens in a
mobile phone, or as a PC, this element allows different child element
combinations to be used. When combined, the values of the child
elements MUST uniquely identify the device. For example, for
hardware tokens, the combination of <SerialNo> and <Manufacturer>
elements uniquely identifies a device, but the <SerialNo> element
alone is insufficient since two different token manufacturers might
issue devices with the same serial number (similar to the Issuer
Distinguished Name and serial number of a certificate).
The <DeviceInfo> element has the following child elements:
<Manufacturer>: This element indicates the manufacturer of the
device. Values for the <Manufacturer> element MUST be taken from
either [OATHMAN] prefixes (i.e., the left column) or from the IANA
Private Enterprise Number Registry [IANAPENREG], using the
Organization value. When the value is taken from [OATHMAN],
"oath." MUST be prepended to the value (e.g., "oath.<prefix value
from [OATHMAN]>"). When the value is taken from [IANAPENREG],
"iana." MUST be prepended to the value (e.g., "iana.<Organization
value from [IANAPENREG]>").
<SerialNo>: This element contains the serial number of the device.
<Model>: This element describes the model of the device (e.g., one-
button-HOTP-token-V1).
<IssueNo>: This element contains the issue number in case there are
devices with the same serial number so that they can be
distinguished by different issue numbers.
<DeviceBinding>: This element allows a provisioning server to ensure
that the key is going to be loaded into the device for which the
key provisioning request was approved. The device is bound to the
request using a device identifier, e.g., an International Mobile
Equipment Identity (IMEI) for the phone, or an identifier for a
class of identifiers, e.g., those for which the keys are protected
by a Trusted Platform Module (TPM).
<StartDate> and <ExpiryDate>: These two elements indicate the start
and end date of a device (such as the one on a payment card, used
when issue numbers are not printed on cards). The date MUST be
expressed as a dateTime value in "canonical representation"
[W3C.REC-xmlschema-2-20041028]. Implementations SHOULD NOT rely
on time resolution finer than milliseconds and MUST NOT generate
time instants that specify leap seconds. Keys that reside on the
device SHOULD only be used when the current date is after the
<StartDate> and before the <ExpiryDate>. Note that usage
enforcement of the keys with respect to the dates MAY only happen
on the validation server, as some devices such as smart cards do
not have an internal clock. Systems thus SHOULD NOT rely upon the
device to enforce key usage date restrictions.
Depending on the device type, certain child elements of the
<DeviceInfo> element MUST be included in order to uniquely identify a
device. This document does not enumerate the different device types
and therefore does not list the elements that are mandatory for each
type of device.
4.3.2. <CryptoModuleInfo> Element: CryptoModule Identification
The <CryptoModuleInfo> element identifies the cryptographic module to
which the symmetric keys are or have been provisioned. This allows
the identification of the specific cases where a device MAY contain
more than one crypto module (e.g., a PC hosting a TPM and a connected
token).
The <CryptoModuleInfo> element has a single child element that MUST
be included:
<Id>: This element carries a unique identifier for the CryptoModule
and is implementation specific. As such, it helps to identify a
specific CryptoModule to which the key is being or was
provisioned.
4.3.3. <UserId> Element: User Identification
The <UserId> element identifies the user of a distinguished name, as
defined in [RFC4514], for example, UID=jsmith,DC=example,DC=net.
Although the syntax of the user identifier is defined, there are no
semantics associated with this element, i.e., there are no checks
enforcing that only a specific user can use this key. As such, this
element is for informational purposes only.
This element may appear in two places, namely as a child element of
the <Key> element, where it indicates the user with whom the key is
associated, and as a child element of the <DeviceInfo> element, where
it indicates the user with whom the device is associated.
4.3.4. <AlgorithmParameters> Element: Supplementary Information for OTP
and CR Algorithms
The <AlgorithmParameters> element is a child element of the <Key>
element, and this document defines three child elements: <Suite>,
<ChallengeFormat>, and <ResponseFormat>.
<Suite>:
The optional <Suite> element defines additional characteristics of
the algorithm used, which are algorithm specific. For example, in
an HMAC-based (Hashed MAC) OTP algorithm, it could designate the
strength of the hash algorithm used (SHA1, SHA256, etc.). Please
refer to the algorithm profile section, Section 10, for the exact
semantics of the value for each algorithm profile.
<ChallengeFormat>:
The <ChallengeFormat> element defines the characteristics of the
challenge in a CR usage scenario whereby the following attributes
are defined:
'Encoding': This attribute, which MUST be included, defines the
encoding of the challenge accepted by the device and MUST be
one of the following values:
DECIMAL: Only numerical digits
HEXADECIMAL: Hexadecimal response
ALPHANUMERIC: All letters and numbers (case sensitive)
BASE64: Base-64 encoded, as defined in Section 4 of [RFC4648]
BINARY: Binary data
'CheckDigit': This attribute indicates whether a device needs to
check the appended Luhn check digit, as defined in
[ISOIEC7812], contained in a challenge. This is only valid if
the 'Encoding' attribute is set to 'DECIMAL'. A value of TRUE
indicates that the device will check the appended Luhn check
digit in a provided challenge. A value of FALSE indicates that
the device will not check the appended Luhn check digit in the
challenge.
'Min': This attribute defines the minimum size of the challenge
accepted by the device for CR mode and MUST be included. If
the 'Encoding' attribute is set to 'DECIMAL', 'HEXADECIMAL', or
'ALPHANUMERIC', this value indicates the minimum number of
digits/characters. If the 'Encoding' attribute is set to
'BASE64' or 'BINARY', this value indicates the minimum number
of bytes of the unencoded value.
'Max': This attribute defines the maximum size of the challenge
accepted by the device for CR mode and MUST be included. If
the 'Encoding' attribute is set to 'DECIMAL', 'HEXADECIMAL', or
'ALPHANUMERIC', this value indicates the maximum number of
digits/characters. If the 'Encoding' attribute is set to
'BASE64' or 'BINARY', this value indicates the maximum number
of bytes of the unencoded value.
<ResponseFormat>:
The <ResponseFormat> element defines the characteristics of the
result of a computation and defines the format of the OTP or the
response to a challenge. For cases in which the key is a PIN
value, this element contains the format of the PIN itself (e.g.,
DECIMAL, length 4 for a 4-digit PIN). The following attributes
are defined:
'Encoding': This attribute defines the encoding of the response
generated by the device, it MUST be included and MUST be one of
the following values: DECIMAL, HEXADECIMAL, ALPHANUMERIC,
BASE64, or BINARY.
'CheckDigit': This attribute indicates whether the device needs
to append a Luhn check digit, as defined in [ISOIEC7812], to
the response. This is only valid if the 'Encoding' attribute
is set to 'DECIMAL'. If the value is TRUE, then the device
will append a Luhn check digit to the response. If the value
is FALSE, then the device will not append a Luhn check digit to
the response.
'Length': This attribute defines the length of the response
generated by the device and MUST be included. If the
'Encoding' attribute is set to 'DECIMAL', 'HEXADECIMAL', or
ALPHANUMERIC, this value indicates the number of digits/
characters. If the 'Encoding' attribute is set to 'BASE64' or
'BINARY', this value indicates the number of bytes of the
unencoded value.
4.4. Transmission of Key Derivation Values
<KeyProfileId> element, which is a child element of the <Key>
element, carries a unique identifier used between the sending and
receiving parties to establish a set of key attribute values that are
not transmitted within the container but are agreed upon between the
two parties out of band. This element will then represent the unique
reference to a set of key attribute values. (For example, a smart
card application personalization profile id related to specific
attribute values present on a smart card application that have
influence when computing a response).
For example, in the case of MasterCard's Chip Authentication Program
[CAP], the sending and the receiving party would agree that
KeyProfileId='1' represents a certain set of values (e.g., Internet
Authentication Flag (IAF) set to a specific value). During
transmission of the <KeyContainer>, these values would not be
transmitted as key attributes but would only be referred to via the
<KeyProfileId> element set to the specific agreed-upon profile (in
this case '1'). The receiving party can then associate all relevant
key attributes contained in the profile that was agreed upon out of
band with the imported keys. Often, this methodology is used between
a manufacturing service, run by company A, and the validation
service, run by company B, to avoid repeated transmission of the same
set of key attribute values.
The <KeyReference> element contains a reference to an external key to
be used with a key derivation scheme. In this case, the parent <Key>
element will not contain the <Secret> subelement of <Data>, in which
the key value (secret) is transported; only the reference to the
external master key is transported (e.g., a PKCS #11 key label).
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0" Id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<KeyPackage>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<CryptoModuleInfo>
<Id>CM_ID_001</Id>
</CryptoModuleInfo>
<Key Id="12345678"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<KeyProfileId>keyProfile1</KeyProfileId>
<KeyReference>MasterKeyLabel
</KeyReference>
<Data>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<KeyUsage>OTP</KeyUsage>
</Policy>
</Key>
</KeyPackage>
</KeyContainer>
Figure 4: Example of a PSKC Document Transmitting an HOTP Key via Key
Derivation Values
The key value will be derived using the value of the <SerialNo>
element, values agreed upon between the sending and the receiving
parties and identified by the <KeyProfile> 'keyProfile1', and an
externally agreed-upon key referenced by the label 'MasterKeyLabel'.
5. Key Policy
This section illustrates the functionality of the <Policy> element
within PSKC, which allows a key usage and key PIN protection policy
to be attached to a specific key and its related metadata. This
element is a child element of the <Key> element.
If the <Policy> element contains child elements or values within
elements/attributes that are not understood by the recipient of the
PSKC document, then the recipient MUST assume that key usage is not
permitted. This statement ensures that the lack of understanding of
certain extensions does not lead to unintended key usage.
We will start our description with an example that expands the
example shown in Figure 3.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer
Version="1.0" Id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<KeyPackage>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<CryptoModuleInfo>
<Id>CM_ID_001</Id>
</CryptoModuleInfo>
<Key Id="12345678"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<PINPolicy MinLength="4" MaxLength="4"
PINKeyId="123456781" PINEncoding="DECIMAL"
PINUsageMode="Local"/>
<KeyUsage>OTP</KeyUsage>
</Policy>
</Key>
</KeyPackage>
<KeyPackage>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<CryptoModuleInfo>
<Id>CM_ID_001</Id>
</CryptoModuleInfo>
<Key Id="123456781"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:pin">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="4" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>MTIzNA==</PlainValue>
</Secret>
</Data>
</Key>
</KeyPackage>
</KeyContainer>
Figure 5: Non-Encrypted HOTP Secret Key Protected by PIN
This document defines the following <Policy> child elements:
<StartDate> and <ExpiryDate>: These two elements denote the validity
period of a key. It MUST be ensured that the key is only used
between the start and the end date (inclusive). The date MUST be
expressed as a dateTime value in "canonical representation"
[W3C.REC-xmlschema-2-20041028]. Implementations SHOULD NOT rely
on time resolution finer than milliseconds and MUST NOT generate
time instants that specify leap seconds. When this element is
absent, the current time is assumed as the start time.
<NumberOfTransactions>: The value in this element indicates the
maximum number of times a key carried within the PSKC document can
be used by an application after having received it. When this
element is omitted, there is no restriction regarding the number
of times a key can be used.
<KeyUsage>: The <KeyUsage> element puts constraints on the intended
usage of the key. The recipient of the PSKC document MUST enforce
the key usage. Currently, the following tokens are registered by
this document:
OTP: The key MUST only be used for OTP generation.
CR: The key MUST only be used for Challenge/Response purposes.
Encrypt: The key MUST only be used for data encryption purposes.
Integrity: The key MUST only be used to generate a keyed message
digest for data integrity or authentication purposes.
Verify: The key MUST only be used to verify a keyed message
digest for data integrity or authentication purposes (this is
the opposite key usage of 'Integrity').
Unlock: The key MUST only be used for an inverse Challenge/
Response in the case where a user has locked the device by
entering a wrong PIN too many times (for devices with PIN-input
capability).
Decrypt: The key MUST only be used for data decryption purposes.
KeyWrap: The key MUST only be used for key wrap purposes.
Unwrap: The key MUST only be used for key unwrap purposes.
Derive: The key MUST only be used with a key derivation function
to derive a new key (see also Section 8.2.4 of [NIST800-57]).
Generate: The key MUST only be used to generate a new key based
on a random number and the previous value of the key (see also
Section 8.1.5.2.1 of [NIST800-57]).
The element MAY also be repeated to allow several key usages to be
expressed. When this element is absent, no key usage constraint
is assumed, i.e., the key MAY be utilized for every usage.
<PINPolicy>: The <PINPolicy> element allows policy about the PIN
usage to be associated with the key. The following attributes are
specified:
'PINKeyId': This attribute carries the unique 'Id' attribute vale
of the <Key> element held within this <KeyContainer> that
contains the value of the PIN that protects the key.
'PINUsageMode': This mandatory attribute indicates the way the
PIN is used during the usage of the key. The following values
are defined:
Local: This value indicates that the PIN is checked locally on
the device before allowing the key to be used in executing
the algorithm.
Prepend: This value indicates that the PIN is prepended to the
algorithm response; hence, it MUST be checked by the party
validating the response.
Append: This value indicates that the PIN is appended to the
algorithm response; hence, it MUST be checked by the party
validating the response.
Algorithmic: This value indicates that the PIN is used as part
of the algorithm computation.
'MaxFailedAttempts': This attribute indicates the maximum number
of times the PIN may be entered wrongly before it MUST NOT be
possible to use the key anymore (typical reasonable values are
in the positive integer range of at least 2 and no more than
10).
'MinLength': This attribute indicates the minimum length of a PIN
that can be set to protect the associated key. It MUST NOT be
possible to set a PIN shorter than this value. If the
'PINFormat' attribute is set to 'DECIMAL', 'HEXADECIMAL', or
'ALPHANUMERIC', this value indicates the number of digits/
characters. If the 'PINFormat' attribute is set to 'BASE64' or
'BINARY', this value indicates the number of bytes of the
unencoded value.
'MaxLength': This attribute indicates the maximum length of a PIN
that can be set to protect this key. It MUST NOT be possible
to set a PIN longer than this value. If the 'PINFormat'
attribute is set to 'DECIMAL', 'HEXADECIMAL', or
'ALPHANUMERIC', this value indicates the number of digits/
characters. If the 'PINFormat' attribute is set to 'BASE64' or
'BINARY', this value indicates the number of bytes of the
unencoded value.
'PINEncoding': This attribute indicates the encoding of the PIN
and MUST be one of the values: DECIMAL, HEXADECIMAL,
ALPHANUMERIC, BASE64, or BINARY.
If the 'PinUsageMode' attribute is set to 'Local', then the device
MUST enforce the restriction indicated in the 'MaxFailedAttempts',
'MinLength', 'MaxLength', and 'PINEncoding' attributes; otherwise,
it MUST be enforced on the server side.
5.1. PIN Algorithm Definition
The PIN algorithm is defined as:
boolean = comparePIN(K,P)
Where:
'K' is the stored symmetric credential (PIN) in binary format.
'P' is the proposed PIN to be compared in binary format.
The function comparePIN is a straight octet comparison of K and P.
Such a comparison MUST yield a value of TRUE (credentials matched)
when the octet length of K is the same as the octet length of P and
all octets comprising K are the same as the octets comprising P.
6. Key Protection Methods
With the functionality described in the previous sections,
information related to keys had to be transmitted in cleartext. With
the help of the <EncryptionKey> element, which is a child element of
the <KeyContainer> element, it is possible to encrypt keys and
associated information. The level of encryption is applied to the
value of individual elements and the applied encryption algorithm
MUST be the same for all encrypted elements. Keys are protected
using the following methods: pre-shared keys, passphrase-based keys,
and asymmetric keys. When encryption algorithms are used that make
use of Initialization Vectors (IVs), for example, AES-128-CBC, a
random IV value MUST be generated for each value to be encrypted and
it MUST be prepended to the resulting encrypted value as specified in
[XMLENC].
6.1. Encryption Based on Pre-Shared Keys
Figure 6 shows an example that illustrates the encryption of the
content of the <Secret> element using AES-128-CBC and PKCS #5
Padding. The plaintext value of <Secret> is
'3132333435363738393031323334353637383930'. The name of the pre-
shared secret is "Pre-shared-key", as set in the <KeyName> element
(which is a child element of the <EncryptionKey> element). The value
of the encryption key used is '12345678901234567890123456789012'.
The IV for the MAC key is '11223344556677889900112233445566', and the
IV for the HOTP key is '000102030405060708090a0b0c0d0e0f'.
As AES-128-CBC does not provide integrity checks, a keyed MAC is
applied to the encrypted value using a MAC key and a MAC algorithm as
declared in the <MACMethod> element (in our example,
"http://www.w3.org/2000/09/xmldsig#hmac-sha1" is used as the
algorithm and the value of the MAC key is randomly generated, in our
case '1122334455667788990011223344556677889900', and encrypted with
the above encryption key). The result of the keyed-MAC computation
is placed in the <ValueMAC> child element of <Secret>.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
<EncryptionKey>
<ds:KeyName>Pre-shared-key</ds:KeyName>
</EncryptionKey>
<MACMethod Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1">
<MACKey>
<xenc:EncryptionMethod
Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
<xenc:CipherData>
<xenc:CipherValue>
ESIzRFVmd4iZABEiM0RVZgKn6WjLaTC1sbeBMSvIhRejN9vJa2BOlSaMrR7I5wSX
</xenc:CipherValue>
</xenc:CipherData>
</MACKey>
</MACMethod>
<KeyPackage>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<CryptoModuleInfo>
<Id>CM_ID_001</Id>
</CryptoModuleInfo>
<Key Id="12345678"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<EncryptedValue>
<xenc:EncryptionMethod
Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
<xenc:CipherData>
<xenc:CipherValue>
AAECAwQFBgcICQoLDA0OD+cIHItlB3Wra1DUpxVvOx2lef1VmNPCMl8jwZqIUqGv
</xenc:CipherValue>
</xenc:CipherData>
</EncryptedValue>
<ValueMAC>Su+NvtQfmvfJzF6bmQiJqoLRExc=
</ValueMAC>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</KeyPackage>
</KeyContainer>
Figure 6: AES-128-CBC Encrypted Pre-Shared Secret Key with HMAC-SHA1
When protecting the payload with pre-shared keys, implementations
MUST set the name of the specific pre-shared key in the <KeyName>
element inside the <EncryptionKey> element. When the encryption
method uses a CBC mode that requires an explicit initialization
vector (IV), the IV MUST be passed by prepending it to the encrypted
value.
For systems implementing PSKC, it is RECOMMENDED to support
AES-128-CBC (with the URI of
http://www.w3.org/2001/04/xmlenc#aes128-cbc) and KW-AES128 (with the
URI of http://www.w3.org/2001/04/xmlenc#kw-aes128). Please note that
KW-AES128 requires that the key to be protected must be a multiple of
8 bytes in length. Hence, if keys of a different length have to be
protected, then the usage of the key-wrap algorithm with padding, as
described in [RFC5649] is RECOMMENDED. Some of the encryption
algorithms that can optionally be implemented are:
Algorithm | Uniform Resource Locator (URL)
---------------+-------------------------------------------------------
AES192-CBC | http://www.w3.org/2001/04/xmlenc#aes192-cbc
AES256-CBC | http://www.w3.org/2001/04/xmlenc#aes256-cbc
TripleDES-CBC | http://www.w3.org/2001/04/xmlenc#tripledes-cbc
Camellia128 | http://www.w3.org/2001/04/xmldsig-more#camellia128
Camellia192 | http://www.w3.org/2001/04/xmldsig-more#camellia192
Camellia256 | http://www.w3.org/2001/04/xmldsig-more#camellia256
KW-AES128 | http://www.w3.org/2001/04/xmlenc#kw-aes128
KW-AES192 | http://www.w3.org/2001/04/xmlenc#kw-aes192
KW-AES256 | http://www.w3.org/2001/04/xmlenc#kw-aes256
KW-TripleDES | http://www.w3.org/2001/04/xmlenc#kw-tripledes
KW-Camellia128 | http://www.w3.org/2001/04/xmldsig-more#kw-camellia128
KW-Camellia192 | http://www.w3.org/2001/04/xmldsig-more#kw-camellia192
KW-Camellia256 | http://www.w3.org/2001/04/xmldsig-more#kw-camellia256
6.1.1. MAC Method
When algorithms without integrity checks are used, such as AES-128-
CBC, a keyed-MAC value MUST be placed in the <ValueMAC> element of
the <Data> element. In this case, the MAC algorithm type MUST be set
in the <MACMethod> element of the <KeyContainer> element. The MAC
key MUST be a randomly generated key by the sender, be pre-agreed
upon between the receiver and the sender, or be set by the
application protocol that carries the PSKC document. It is
RECOMMENDED that the sender generate a random MAC key. When the
sender generates such a random MAC key, the MAC key material MUST be
encrypted with the same encryption key specified in <EncryptionKey>
element of the key container. The encryption method and encrypted
value MUST be set in the <EncryptionMethod> element and the
<CipherData> element, respectively, of the <MACKey> element in the
<MACMethod> element. The <MACKeyReference> element of the
<MACMethod> element MAY be used to indicate a pre-shared MAC key or a
provisioning protocol derived MAC key. For systems implementing
PSKC, it is RECOMMENDED to implement the HMAC-SHA1 (with the URI of
'http://www.w3.org/2000/09/xmldsig#hmac-sha1'). Some of the MAC
algorithms that can optionally be implemented are:
Algorithm | Uniform Resource Locator (URL)
---------------+-----------------------------------------------------
HMAC-SHA224 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha224
HMAC-SHA256 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha256
HMAC-SHA384 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha384
HMAC-SHA512 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha512
6.2. Encryption Based on Passphrase-Based Keys
Figure 7 shows an example that illustrates the encryption of the
content of the <Secret> element using passphrase-based key derivation
(PBKDF2) to derive the encryption key as defined in [PKCS5]. When
using passphrase-based key derivation, the <DerivedKey> element
defined in XML Encryption Version 1.1 [XMLENC11] MUST be used to
specify the passphrased-based key. A <DerivedKey> element is set as
the child element of <EncryptionKey> element of the key container.
The <DerivedKey> element is used to specify the key derivation
function and related parameters. The encryption algorithm, in this
example, AES-128-CBC (URI
'http://www.w3.org/2001/04/xmlenc#aes128-cbc'), MUST be set in the
'Algorithm' attribute of <EncryptionMethod> element used inside the
encrypted data elements.
When PBKDF2 is used, the 'Algorithm' attribute of the <xenc11:
KeyDerivationMethod> element MUST be set to the URI
'http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbkdf2'. The
<xenc11:KeyDerivationMethod> element MUST include the <PBKDF2-params>
child element to indicate the PBKDF2 parameters, such as salt and
iteration count.
When the encryption method uses a CBC mode that uses an explicit
initialization vector (IV) other than a derived one, the IV MUST be
passed by prepending it to the encrypted value.
In the example below, the following data is used.
Password: qwerty
Salt: 0x123eff3c4a72129c
Iteration Count: 1000
MAC Key: 0xbdaab8d648e850d25a3289364f7d7eaaf53ce581
OTP Secret: 12345678901234567890
The derived encryption key is "0x651e63cd57008476af1ff6422cd02e41".
The initialization vector (IV) is
"0xa13be8f92db69ec992d99fd1b5ca05f0". This key is also used to
encrypt the randomly chosen MAC key. A different IV can be used, say
"0xd864d39cbc0cdc8e1ee483b9164b9fa0", in the example. The encryption
with algorithm "AES-128-CBC" follows the specification defined in
[XMLENC].
<?xml version="1.0" encoding="UTF-8"?>
<pskc:KeyContainer
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
xmlns:xenc11="http://www.w3.org/2009/xmlenc11#"
xmlns:pkcs5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Version="1.0">
<pskc:EncryptionKey>
<xenc11:DerivedKey>
<xenc11:KeyDerivationMethod
Algorithm=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#pbkdf2">
<pkcs5:PBKDF2-params>
<Salt>
<Specified>Ej7/PEpyEpw=</Specified>
</Salt>
<IterationCount>1000</IterationCount>
<KeyLength>16</KeyLength>
<PRF/>
</pkcs5:PBKDF2-params>
</xenc11:KeyDerivationMethod>
<xenc:ReferenceList>
<xenc:DataReference URI="#ED"/>
</xenc:ReferenceList>
<xenc11:MasterKeyName>My Password 1</xenc11:MasterKeyName>
</xenc11:DerivedKey>
</pskc:EncryptionKey>
<pskc:MACMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1">
<pskc:MACKey>
<xenc:EncryptionMethod
Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
<xenc:CipherData>
<xenc:CipherValue>
2GTTnLwM3I4e5IO5FkufoOEiOhNj91fhKRQBtBJYluUDsPOLTfUvoU2dStyOwYZx
</xenc:CipherValue>
</xenc:CipherData>
</pskc:MACKey>
</pskc:MACMethod>
<pskc:KeyPackage>
<pskc:DeviceInfo>
<pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>
<pskc:SerialNo>987654321</pskc:SerialNo>
</pskc:DeviceInfo>
<pskc:CryptoModuleInfo>
<pskc:Id>CM_ID_001</pskc:Id>
</pskc:CryptoModuleInfo>
<pskc:Key Algorithm=
"urn:ietf:params:xml:ns:keyprov:pskc:hotp" Id="123456">
<pskc:Issuer>Example-Issuer</pskc:Issuer>
<pskc:AlgorithmParameters>
<pskc:ResponseFormat Length="8" Encoding="DECIMAL"/>
</pskc:AlgorithmParameters>
<pskc:Data>
<pskc:Secret>
<pskc:EncryptedValue Id="ED">
<xenc:EncryptionMethod
Algorithm=
"http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
<xenc:CipherData>
<xenc:CipherValue>
oTvo+S22nsmS2Z/RtcoF8Hfh+jzMe0RkiafpoDpnoZTjPYZu6V+A4aEn032yCr4f
</xenc:CipherValue>
</xenc:CipherData>
</pskc:EncryptedValue>
<pskc:ValueMAC>LP6xMvjtypbfT9PdkJhBZ+D6O4w=
</pskc:ValueMAC>
</pskc:Secret>
</pskc:Data>
</pskc:Key>
</pskc:KeyPackage>
</pskc:KeyContainer>
Figure 7: Example of a PSKC Document Using Encryption Based on
Passphrase-Based Keys
6.3. Encryption Based on Asymmetric Keys
When using asymmetric keys to encrypt child elements of the <Data>
element, information about the certificate being used MUST be stated
in the <X509Data> element, which is a child element of the
<EncryptionKey> element. The encryption algorithm MUST be indicated
in the 'Algorithm' attribute of the <EncryptionMethod> element. In
the example shown in Figure 8, the algorithm is set to
'http://www.w3.org/2001/04/xmlenc#rsa_1_5'.
<?xml version="1.0" encoding="UTF-8" ?>
<KeyContainer
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
Id="KC0001"
EID 3370 (Verified) is as follows:Section: 6.3
Original Text:
id="KC0001"
Corrected Text:
Id="KC0001"
Notes:
The PSKC data in figure 8 does not pass a XML Schema validation -- the reason is a typo in the Id attribute name.
Version="1.0">
<EncryptionKey>
<ds:X509Data>
<ds:X509Certificate>MIIB5zCCAVCgAwIBAgIESZp/vDANBgkqhkiG9w0BAQUFADA4M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</ds:X509Certificate>
</ds:X509Data>
</EncryptionKey>
<KeyPackage>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key
Id="MBK000000001"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Example-Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="6" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<EncryptedValue>
<xenc:EncryptionMethod
Algorithm="http://www.w3.org/2001/04/xmlenc#rsa_1_5"/>
<xenc:CipherData>
<xenc:CipherValue>hJ+fvpoMPMO9BYpK2rdyQYGIxiATYHTHC7e/sPLKYo5/r1v+4
xTYG3gJolCWuVMydJ7Ta0GaiBPHcWa8ctCVYmHKfSz5fdeV5nqbZApe6dofTqhRwZK6
Yx4ufevi91cjN2vBpSxYafvN3c3+xIgk0EnTV4iVPRCR0rBwyfFrPc4=
</xenc:CipherValue>
</xenc:CipherData>
</EncryptedValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</KeyPackage>
</KeyContainer>
Figure 8: Example of a PSKC Document Using Encryption Based on
Asymmetric Keys
For systems implementing PSKC, it is RECOMMENDED to implement the
RSA-1.5 algorithm, identified by the URI
'http://www.w3.org/2001/04/xmlenc#rsa-1_5'.
Some of the asymmetric encryption algorithms that can optionally be
implemented are:
Algorithm | Uniform Resource Locator (URL)
------------------+-------------------------------------------------
RSA-OAEP-MGF1P | http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p
6.4. Padding of Encrypted Values for Non-Padded Encryption Algorithms
Padding of encrypted values (for example, the key secret value) is
required when key protection algorithms are used that do not support
embedded padding and the value to be encrypted is not a multiple of
the encryption algorithm cipher block length.
For example, when transmitting an HOTP key (20 bytes long) protected
with the AES algorithm in CBC mode (8-byte block cipher), padding is
required since its length is not a multiple of the 8-byte block
length.
In these cases, for systems implementing PSKC, it is RECOMMENDED to
pad the value before encryption using PKCS #5 padding as described in
[PKCS5].
7. Digital Signature
EID 3418 (Verified) is as follows:Section: 7 and 11
Original Text:
Section 7:
<Signature>
Section 11:
<xs:element name="Signature"
type="ds:SignatureType" minOccurs="0"/>
Corrected Text:
Section 7:
<ds:Signature>
Section 11:
<xs:element ref="ds:Signature" minOccurs="0"/>
Notes:
It seems the Signature element is in the wrong namespace, making PSKC incompatible with the XMLDsig specification.
There is a thread on this on the XMLSec mailing list:
PSKC allows a digital signature to be added to the XML document, as a
child element of the <KeyContainer> element. The description of the
XML digital signature can be found in [XMLDSIG].
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer
xmlns="urn:ietf:params:xml:ns:keyprov:pskc"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
Version="1.0">
<KeyPackage>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>0755225266</SerialNo>
</DeviceInfo>
<Key Id="123"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Example-Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="6" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>
MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</KeyPackage>
<Signature>
<ds:SignedInfo>
<ds:CanonicalizationMethod
Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
<ds:SignatureMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
<ds:Reference URI="#Device">
<ds:DigestMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<ds:DigestValue>
j6lwx3rvEPO0vKtMup4NbeVu8nk=
</ds:DigestValue>
</ds:Reference>
</ds:SignedInfo>
<ds:SignatureValue>
j6lwx3rvEPO0vKtMup4NbeVu8nk=
</ds:SignatureValue>
<ds:KeyInfo>
<ds:X509Data>
<ds:X509IssuerSerial>
<ds:X509IssuerName>
CN=Example.com,C=US
</ds:X509IssuerName>
<ds:X509SerialNumber>
12345678
</ds:X509SerialNumber>
</ds:X509IssuerSerial>
</ds:X509Data>
</ds:KeyInfo>
</Signature>
</KeyContainer>
Figure 9: Digital Signature Example
8. Bulk Provisioning
The functionality of bulk provisioning can be accomplished by
repeating the <KeyPackage> element multiple times within the
<KeyContainer> element, indicating that multiple keys are provided to
different devices or cryptographic modules. The <EncryptionKey>
element then applies to all <KeyPackage> elements. When provisioning
multiple keys to the same device, the <KeyPackage> element is
repeated, but the enclosed <DeviceInfo> element will contain the same
sub-elements that uniquely identify the single device (for example,
the keys for the device identified by SerialNo='9999999' in the
example below).
Figure 10 shows an example utilizing these capabilities.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<KeyPackage>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>654321</SerialNo>
</DeviceInfo>
<Key Id="1"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>
MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<StartDate>2006-05-01T00:00:00Z</StartDate>
<ExpiryDate>2006-05-31T00:00:00Z</ExpiryDate>
</Policy>
</Key>
</KeyPackage>
<KeyPackage>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>123456</SerialNo>
</DeviceInfo>
<Key Id="2"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>
MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<StartDate>2006-05-01T00:00:00Z</StartDate>
<ExpiryDate>2006-05-31T00:00:00Z</ExpiryDate>
</Policy>
</Key>
</KeyPackage>
<KeyPackage>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>9999999</SerialNo>
</DeviceInfo>
<Key Id="3"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>
MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<StartDate>2006-03-01T00:00:00Z</StartDate>
<ExpiryDate>2006-03-31T00:00:00Z</ExpiryDate>
</Policy>
</Key>
</KeyPackage>
<KeyPackage>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>9999999</SerialNo>
</DeviceInfo>
<Key Id="4"
Algorithm="urn:ietf:params:xml:ns:keyprov:pskc:hotp">
<Issuer>Issuer</Issuer>
<AlgorithmParameters>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</AlgorithmParameters>
<Data>
<Secret>
<PlainValue>
MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<StartDate>2006-04-01T00:00:00Z</StartDate>
<ExpiryDate>2006-04-30T00:00:00Z</ExpiryDate>
</Policy>
</Key>
</KeyPackage>
</KeyContainer>
Figure 10: Bulk Provisioning Example
9. Extensibility
This section lists a few common extension points provided by PSKC:
New PSKC Version: Whenever it is necessary to define a new version
of this document, a new version number has to be allocated to
refer to the new specification. The version number is carried
inside the 'Version' attribute, as described in Section 4, the
numbering scheme MUST follow Section 1.2, and rules for
extensibility are defined in Section 12.
New XML Elements: The usage of the XML schema and the available
extension points allows new XML elements to be added. Depending
on the type of XML element, different ways for extensibility are
offered. In some places, the <Extensions> element can be used and
elsewhere the "<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>" XML extension point is
utilized.
New XML Attributes: The XML schema allows new XML attributes to be
added where XML extension points have been defined (see "<xs:
anyAttribute namespace="##other"/>" in Section 11).
New PSKC Algorithm Profiles: This document defines two PSKC
algorithm profiles, see Section 10. The following informational
document describes additional profiles [PSKC-ALGORITHM-PROFILES].
Further PSKC algorithm profiles can be registered as described in
Section 12.4.
Algorithm URIs: Section 6 defines how keys and related data can be
protected. A number of algorithms can be used. New algorithms
can be used by pointing to a new algorithm URI.
Policy: Section 5 defines policies that can be attached to a key and
keying-related data. The <Policy> element is one such item that
allows implementers to restrict the use of the key to certain
functions, such as "OTP usage only". Further values may be
registered as described in Section 12.
10. PSKC Algorithm Profile
10.1. HOTP
Common Name: HOTP
Class: OTP
URI: urn:ietf:params:xml:ns:keyprov:pskc:hotp
Algorithm Definition: [HOTP]
Identifier Definition: (this RFC)
Registrant Contact: IESG
Deprecated: FALSE
Profiling:
The <KeyPackage> element MUST be present and the
<ResponseFormat> element, which is a child element of the
<AlgorithmParameters> element, MUST be used to indicate the OTP
length and the value format.
The <Counter> element (see Section 4.1) MUST be provided as
metadata for the key.
The following additional constraints apply:
+ The value of the <Secret> element MUST contain key material
with a length of at least 16 octets (128 bits), if it is
present.
+ The <ResponseFormat> element MUST have the 'Format'
attribute set to "DECIMAL", and the 'Length' attribute MUST
indicate a length value between 6 and 9 (inclusive).
+ The <PINPolicy> element MAY be present, but the
'PINUsageMode' attribute cannot be set to "Algorithmic".
An example can be found in Figure 3.
10.2. PIN
Common Name: PIN
Class: Symmetric static credential comparison
URI: urn:ietf:params:xml:ns:keyprov:pskc:pin
Algorithm Definition: (this RFC) Section 5.1
Identifier Definition (this RFC)
Registrant Contact: IESG
Deprecated: FALSE
Profiling:
The <AlgorithmParameters> element MAY be present, but no attribute
of the <AlgorithmParameters> element is required. The <ResponseFormat> element MAY
EID 2621 (Verified) is as follows:Section: 10.2
Original Text:
The <Usage> element MAY be present, but no attribute of the
<Usage> element is required.
Corrected Text:
The <AlgorithmParameters> element MAY be present, but no attribute
of the <AlgorithmParameters> element is required.
Notes:
The <Usage> field was renamed between draft -02 and -03 but this section was not updated.
Notes:
The AlgorithmParameter should have a sequqnce of subelements not a choice as for Challenge/Response algorithms it MUST be possible to define both the ChallengeFormat and the Response Format at the same time. Currently the schema uses <xs:choice> which allows either <ChallengeFormat> or <ResponseFormat> but not both. This correction will bring it in line with intended description in Section 4.3.4
<xs:complexType name="ExtensionsType">
<xs:sequence>
<xs:any namespace="##other"
processContents="lax" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="definition"
type="xs:anyURI" use="optional"/>
</xs:complexType>
<xs:simpleType name="KeyAlgorithmType">
<xs:restriction base="xs:anyURI"/>
</xs:simpleType>
<xs:simpleType name="ValueFormatType">
<xs:restriction base="xs:string">
<xs:enumeration value="DECIMAL"/>
<xs:enumeration value="HEXADECIMAL"/>
<xs:enumeration value="ALPHANUMERIC"/>
<xs:enumeration value="BASE64"/>
<xs:enumeration value="BINARY"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="MACMethodType">
<xs:sequence>
<xs:choice>
<xs:element name="MACKey"
type="xenc:EncryptedDataType" minOccurs="0"/>
<xs:element name="MACKeyReference"
type="xs:string" minOccurs="0"/>
</xs:choice>
<xs:any namespace="##other"
processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="Algorithm" type="xs:anyURI" use="required"/>
</xs:complexType>
<xs:element name="KeyContainer"
type="pskc:KeyContainerType"/>
</xs:schema>
12. IANA Considerations
12.1. Content-Type Registration for 'application/pskc+xml'
This specification contains the registration of a new media type
according to the procedures of RFC 4288 [RFC4288] and guidelines in
RFC 3023 [RFC3023].
MIME media type name: application
MIME subtype name: pskc+xml
Required parameters: There is no required parameter.
Optional parameters: charset
Indicates the character encoding of enclosed XML.
Encoding considerations: Uses XML, which can employ 8-bit
characters, depending on the character encoding used. See RFC
3023 [RFC3023], Section 3.2.
Security considerations: Please refer to Section 13 of RFC 6030.
Interoperability considerations: None
Published specification: RFC 6030.
Applications which use this media type: This media type is being
used as a symmetric key container format for transport and
provisioning of symmetric keys (One-Time Password (OTP) shared
secrets or symmetric cryptographic keys) to different types of
strong authentication devices. As such, it is used for key
provisioning systems.
Additional information:
Magic Number: None
File Extension: .pskcxml
Macintosh file type code: 'TEXT'
Personal and email address to contact for further information:
Philip Hoyer, Philip.Hoyer@actividentity.com
Intended usage: LIMITED USE
Restrictions on usage: None
Author: This specification is a work item of the IETF KEYPROV
working group, with mailing list address <keyprov@ietf.org>.
Change controller: The IESG <iesg@ietf.org>
12.2. XML Schema Registration
This section registers an XML schema as per the guidelines in
[RFC3688].
URI: urn:ietf:params:xml:schema:keyprov:pskc
Registrant Contact: IETF KEYPROV Working Group, Philip Hoyer
(Philip.Hoyer@actividentity.com).
XML Schema: The XML schema to be registered is contained in
Section 11. Its first line is
<?xml version="1.0" encoding="UTF-8"?>
and its last line is
</xs:schema>
12.3. URN Sub-Namespace Registration
This section registers a new XML namespace,
"urn:ietf:params:xml:ns:keyprov:pskc", per the guidelines in
[RFC3688].
URI: urn:ietf:params:xml:ns:keyprov:pskc
Registrant Contact: IETF KEYPROV Working Group, Philip Hoyer
(Philip.Hoyer@actividentity.com).
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>PSKC Namespace</title>
</head>
<body>
<h1>Namespace for PSKC</h1>
<h2>urn:ietf:params:xml:ns:keyprov:pskc</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc6030.txt">
RFC 6030</a>.</p>
</body>
</html>
END
12.4. PSKC Algorithm Profile Registry
IANA has created a registry for PSKC algorithm profiles in accordance
with the principles set out in RFC 5226 [RFC5226].
As part of this registry, IANA maintains the following information:
Common Name: The name by which the PSKC algorithm profile is
generally referred.
Class: The type of PSKC algorithm profile registry entry being
created, such as encryption, Message Authentication Code (MAC),
One-Time Password (OTP), Digest.
URI: The URI to be used to identify the profile.
Identifier Definition: IANA will add a pointer to the specification
containing information about the PSKC algorithm profile
registration.
Algorithm Definition: A reference to the stable document in which
the algorithm being used with the PSKC is defined.
Registrant Contact: Contact information about the party submitting
the registration request.
Deprecated: TRUE if this entry has been deprecated based on expert
approval and SHOULD not be used in any new implementations.
Otherwise, FALSE.
PSKC Profiling: Information about PSKC XML elements and attributes
being used (or not) with this specific profile of PSKC.
PSKC algorithm profile identifier registrations are to be subject to
Specification Required as per RFC 5226 [RFC5226]. Updates can be
provided based on expert approval only. Based on expert approval, it
is possible to mark entries as "deprecated". A designated expert
will be appointed by the IESG.
IANA has added two initial values to the registry based on the
algorithm profiles described in Section 10.
12.5. PSKC Version Registry
IANA has created a registry for PSKC version numbers. The registry
has the following structure:
PSKC Version | Specification
+---------------------------+----------------
| 1.0 | RFC 6030
Standards action is required to define new versions of PSKC. It is
not envisioned to deprecate, delete, or modify existing PSKC
versions.
12.6. Key Usage Registry
IANA has created a registry for key usage. A description of the
<KeyUsage> element can be found in Section 5.
As part of this registry IANA will maintain the following
information:
Key Usage: The identifier of the Key Usage.
Specification: IANA will add a pointer to the specification
containing information about the semantics of a new Key Usage
registration.
Deprecated: TRUE if this entry has been deprecated based on expert
approval and SHOULD not be used in any new implementations.
Otherwise, FALSE.
IANA has added these initial values to the registry:
Key Usage | Specification | Deprecated
+---------------+------------------------------+-----------
| OTP | [Section 5 of this document] | FALSE
| CR | [Section 5 of this document] | FALSE
| Encrypt | [Section 5 of this document] | FALSE
| Integrity | [Section 5 of this document] | FALSE
| Verify | [Section 5 of this document] | FALSE
| Unlock | [Section 5 of this document] | FALSE
| Decrypt | [Section 5 of this document] | FALSE
| KeyWrap | [Section 5 of this document] | FALSE
| Unwrap | [Section 5 of this document] | FALSE
| Derive | [Section 5 of this document] | FALSE
| Generate | [Section 5 of this document] | FALSE
+---------------+------------------------------+-----------
Key Usage Registry registrations are to be subject to Specification
Required as per RFC 5226 [RFC5226]. Expert Review is required to
define new Key Usage values. Updates can be provided based on expert
approval only. Based on expert approval, it is possible to mark
entries as "deprecated". A designated expert will be appointed by
the IESG.
13. Security Considerations
The portable symmetric key container (PSKC) carries sensitive
information (e.g., cryptographic keys) and may be transported across
the boundaries of one secure perimeter to another. For example, a
container residing within the secure perimeter of a back-end
provisioning server in a secure room may be transported across the
Internet to an end-user device attached to a personal computer. This
means that special care MUST be taken to ensure the confidentiality,
integrity, and authenticity of the information contained within.
13.1. PSKC Confidentiality
By design, the container allows two main approaches to guaranteeing
the confidentiality of the information it contains while transported.
First, the container key data payload may be encrypted.
In this case, no transport layer security is required. However,
standard security best practices apply when selecting the strength of
the cryptographic algorithm for key data payload encryption. A
symmetric cryptographic cipher SHOULD be used -- the longer the
cryptographic key, the stronger the protection. Please see
Section 6.1 for recommendations of key data payload protection using
symmetric cryptographic ciphers. In cases where the exchange of key
encryption keys between the sender and the receiver is not possible,
asymmetric encryption of the key data payload may be employed, see
Section 6.3. Similar to symmetric key cryptography, the stronger the
asymmetric key, the more secure the protection.
If the key data payload is encrypted with a method that uses one of
the password-based encryption methods (PBE methods) detailed in
Section 6.2, the key data payload may be subjected to password
dictionary attacks to break the encryption password and recover the
information. Standard security best practices for selection of
strong encryption passwords apply.
Additionally, it is strongly RECOMMENDED that practical
implementations use PBESalt and PBEIterationCount when PBE encryption
is used. A different PBESalt value per PSKC SHOULD be used for best
protection.
The second approach to protecting the confidentiality of the key data
is based on using lower-layer security mechanisms (e.g., [TLS],
[IPsec]). The secure connection established between the source
secure perimeter (the provisioning server from the example above) and
the target perimeter (the device attached to the end-user computer)
utilizes encryption to protect the messages that travel across that
connection. No key data payload encryption is required in this mode.
Secure connections that encrypt and digest each message provide an
extra measure of security.
Because of the fact that the plaintext PSKC is protected only by the
transport layer security, practical implementation MUST ensure
protection against man-in-the-middle attacks. Authenticating the
secure channel endpoints is critically important for eliminating
intruders that may compromise the confidentiality of the PSKC.
13.2. PSKC Integrity
The PSKC provides means to guarantee the integrity of the information
it contains through the use of digital signatures. It is RECOMMENDED
that for best security practices, the digital signature of the
container encompasses the entire PSKC. This provides assurances for
the integrity of all attributes. It also allows verification of the
integrity of a given PSKC even after the container is delivered
through the communication channel to the target perimeter and channel
message integrity check is no longer possible.
13.3. PSKC Authenticity
The digital signature of the PSKC is the primary way of showing its
authenticity. The recipient of the container SHOULD use the public
key associated with the signature to assert the authenticity of the
sender by tracing it back to a pre-loaded public key or certificate.
Note that the digital signature of the PSKC can be checked even after
the container has been delivered through the secure channel of
communication.
Authenticity guarantee may be provided by [TLS] or [IPsec]. However,
no authenticity verification is possible once the container is
delivered at the recipient end. Since the TLS endpoints could differ
from the key provisioning endpoints, this solution is weaker than the
previous solution that relies on a digital signature of the PSKC.
14. Contributors
We would like Hannes Tschofenig for his text contributions to this
document.
15. Acknowledgements
The authors of this document would like to thank the following people
for their feedback: Apostol Vassilev, Shuh Chang, Jon Martinson,
Siddhart Bajaj, Stu Vaeth, Kevin Lewis, Philip Hallam-Baker, Andrea
Doherty, Magnus Nystrom, Tim Moses, Anders Rundgren, Sean Turner, and
especially Robert Philpott.
We would like to thank Sean Turner for his review in January 2009.
We would also like to thank Anders Rundgren for triggering the
discussion regarding to the selection of encryption algorithms
(KW-AES-128 vs. AES-128-CBC) and his input on the keyed message
digest computation.
This work is based on earlier work by the members of OATH (Initiative
for Open AuTHentication), see [OATH], to specify a format that can be
freely distributed to the technical community.
16. References
16.1. Normative References
[FIPS197] National Institute of Standards, "FIPS Pub 197: Advanced
Encryption Standard (AES)", November 2001.
[HOTP] M'Raihi, D., Bellare, M., Hoornaert, F., Naccache, D., and
O. Ranen, "HOTP: An HMAC-Based One-Time Password
Algorithm", RFC 4226, December 2005.
[IANAPENREG]
IANA, "Private Enterprise Numbers", <http://www.iana.org>.
[ISOIEC7812]
ISO, "ISO/IEC 7812-1:2006 Identification cards --
Identification of issuers -- Part 1: Numbering system",
October 2006, <http://www.iso.org/iso/iso_catalogue/
catalogue_tc/catalogue_detail.htm?csnumber=39698>.
[OATHMAN] OATH, "List of OATH Manufacturer Prefixes (omp)",
April 2009,
<http://www.openauthentication.org/oath-id/prefixes/>.
[PKCS5] RSA Laboratories, "PKCS #5: Password-Based Cryptography
Standard", Version 2.0, March 1999,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[RFC4514] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): String Representation of Distinguished Names",
RFC 4514, June 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5646] Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 5646, September 2009.
[RFC5649] Housley, R. and M. Dworkin, "Advanced Encryption Standard
(AES) Key Wrap with Padding Algorithm", RFC 5649,
September 2009.
[SP800-67]
National Institute of Standards, "NIST Special Publication
800-67 Version 1.1: Recommendation for the Triple Data
Encryption Algorithm (TDEA) Block Cipher", NIST Special
Publication 800-67, May 2008.
[W3C.REC-xmlschema-2-20041028]
Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
Second Edition", World Wide Web Consortium
Recommendation REC-xmlschema-2-20041028, October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.
[XMLDSIG] Solo, D., Reagle, J., and D. Eastlake, "XML-Signature
Syntax and Processing", World Wide Web Consortium
FirstEdition REC-xmldsig-core-20020212, February 2002,
<http://www.w3.org/TR/2002/REC-xmldsig-core-20020212>.
[XMLENC] Eastlake, D., "XML Encryption Syntax and Processing.",
W3C Recommendation, December 2002,
<http://www.w3.org/TR/xmlenc-core/>.
[XMLENC11]
Reagle, J. and D. Eastlake, "XML Encryption Syntax and
Processing Version 1.1", World Wide Web Consortium WD WD-
xmlenc-core1-20090730, July 2009,
<http://www.w3.org/TR/2009/WD-xmlenc-core1-20090730>.
16.2. Informative References
[CAP] MasterCard International, "Chip Authentication Program
Functional Architecture", September 2004.
[IPsec] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[NIST800-57]
Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid,
"NIST Special Publication 800-57, Recommendation for Key
Management Part 1: General (Revised)", NIST Special
Publication 800-57, March 2007.
[OATH] "Initiative for Open AuTHentication",
<http://www.openauthentication.org>.
[PSKC-ALGORITHM-PROFILES]
Hoyer, P., Pei, M., Machani, S., and A. Doherty,
"Additional Portable Symmetric Key Container (PSKC)
Algorithm Profiles", Work in Progress, May 2010.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[XMLNS] Hollander, D., Bray, T., and A. Layman, "Namespaces in
XML", World Wide Web Consortium FirstEdition REC-xml-
names-19990114, January 1999,
<http://www.w3.org/TR/1999/REC-xml-names-19990114>.
Appendix A. Use Cases
This section describes a comprehensive list of use cases that
inspired the development of this specification. These requirements
were used to derive the primary requirement that drove the design.
These requirements are covered in the next section.
These use cases also help in understanding the applicability of this
specification to real-world situations.
A.1. Online Use Cases
This section describes the use cases related to provisioning the keys
using an online provisioning protocol.
A.1.1. Transport of Keys from Server to Cryptographic Module
For example, a mobile device user wants to obtain a symmetric key for
use with a cryptographic module on the device. The cryptographic
module from vendor A initiates the provisioning process against a
provisioning system from vendor B using a standards-based
provisioning protocol. The provisioning entity delivers one or more
keys in a standard format that can be processed by the mobile device.
For example, in a variation of the above, instead of the user's
mobile phone, a key is provisioned in the user's soft token
application on a laptop using a network-based online protocol. As
before, the provisioning system delivers a key in a standard format
that can be processed by the soft token on the PC.
For example, the end user or the key issuer wants to update or
configure an existing key in the cryptographic module and requests a
replacement key container. The container may or may not include a
new key and may include new or updated key attributes such as a new
counter value in HOTP key case, a modified response format or length,
a new friendly name, etc.
A.1.2. Transport of Keys from Cryptographic Module to Cryptographic
Module
For example, a user wants to transport a key from one cryptographic
module to another. There may be two cryptographic modules, one on a
computer and one on a mobile phone, and the user wants to transport a
key from the computer to the mobile phone. The user can export the
key and related data in a standard format for input into the other
cryptographic module.
A.1.3. Transport of Keys from Cryptographic Module to Server
For example, a user wants to activate and use a new key and related
data against a validation system that is not aware of this key. This
key may be embedded in the cryptographic module (e.g., a Secure
Digital (SD) card, USB drive) that the user has purchased at the
local electronics retailer. Along with the cryptographic module, the
user may get the key on a CD or a floppy in a standard format. The
user can now upload via a secure online channel or import this key
and related data into the new validation system and start using the
key.
A.1.4. Server-to-Server Bulk Import/Export of Keys
From time to time, a key management system may be required to import
or export keys in bulk from one entity to another.
For example, instead of importing keys from a manufacturer using a
file, a validation server may download the keys using an online
protocol. The keys can be downloaded in a standard format that can
be processed by a validation system.
For example, in a variation of the above, an Over-The-Air (OTA) key
provisioning gateway that provisions keys to mobile phones may obtain
key material from a key issuer using an online protocol. The keys
are delivered in a standard format that can be processed by the key
provisioning gateway and subsequently sent to the mobile phone of the
end user.
A.2. Offline Use Cases
This section describes the use cases relating to offline transport of
keys from one system to another, using some form of export and import
model.
A.2.1. Server-to-Server Bulk Import/Export of Keys
For example, cryptographic modules, such as OTP authentication
tokens, may have their symmetric keys initialized during the
manufacturing process in bulk, requiring copies of the keys and
algorithm data to be loaded into the authentication system through a
file on portable media. The manufacturer provides the keys and
related data in the form of a file containing records in standard
format, typically on a CD. Note that the token manufacturer and the
vendor for the validation system may be the same or different. Some
crypto modules will allow local PIN management (the device will have
a PIN pad); hence, random initial PINs set at manufacturing should be
transmitted together with the respective keys they protect.
For example, an enterprise wants to port keys and related data from
an existing validation system A into a different validation system B.
The existing validation system provides the enterprise with a
functionality that enables export of keys and related data (e.g., for
OTP authentication tokens) in a standard format. Since the OTP
tokens are in the standard format, the enterprise can import the
token records into the new validation system B and start using the
existing tokens. Note that the vendors for the two validation
systems may be the same or different.
Appendix B. Requirements
This section outlines the most relevant requirements that are the
basis of this work. Several of the requirements were derived from
use cases described above.
R1: The format MUST support the transport of multiple types of
symmetric keys and related attributes for algorithms including
HOTP, other OTP, Challenge/Response, etc.
R2: The format MUST handle the symmetric key itself as well of
attributes that are typically associated with symmetric keys.
Some of these attributes may be
* Unique Key Identifier
* Issuer information
* Algorithm ID
* Algorithm mode
* Issuer Name
* Key friendly name
* Event counter value (moving factor for OTP algorithms)
* Time value
R3: The format SHOULD support both offline and online scenarios.
That is, it should be serializable to a file as well as it
should be possible to use this format in online provisioning
protocols.
R4: The format SHOULD allow bulk representation of symmetric keys.
R5: The format SHOULD allow bulk representation of PINs related to
specific keys.
R6: The format SHOULD be portable to various platforms.
Furthermore, it SHOULD be computationally efficient to process.
R7: The format MUST provide an appropriate level of security in
terms of data encryption and data integrity.
R8: For online scenarios, the format SHOULD NOT rely on transport
layer security (e.g., Secure Socket Layer/Transport Layer
Security (SSL/TLS)) for core security requirements.
R9: The format SHOULD be extensible. It SHOULD enable extension
points allowing vendors to specify additional attributes in the
future.
R10: The format SHOULD allow for distribution of key derivation data
without the actual symmetric key itself. This is to support
symmetric key management schemes that rely on key derivation
algorithms based on a pre-placed master key. The key
derivation data typically consists of a reference to the key,
rather than the key value itself.
R11: The format SHOULD allow for additional life cycle management
operations such as counter resynchronization. Such processes
require confidentiality between client and server, thus could
use a common secure container format, without the transfer of
key material.
R12: The format MUST support the use of pre-shared symmetric keys to
ensure confidentiality of sensitive data elements.
R13: The format MUST support a password-based encryption (PBE)
[PKCS5] scheme to ensure security of sensitive data elements.
This is a widely used method for various provisioning
scenarios.
R14: The format SHOULD support asymmetric encryption algorithms such
as RSA to ensure end-to-end security of sensitive data
elements. This is to support scenarios where a pre-set shared
key encryption key is difficult to use.
Authors' Addresses
Philip Hoyer
ActivIdentity, Inc.
117 Waterloo Road
London, SE1 8UL
UK
Phone: +44 (0) 20 7960 0220
EMail: phoyer@actividentity.com
Mingliang Pei
VeriSign, Inc.
487 E. Middlefield Road
Mountain View, CA 94043
USA
Phone: +1 650 426 5173
EMail: mpei@verisign.com
Salah Machani
Diversinet, Inc.
2225 Sheppard Avenue East
Suite 1801
Toronto, Ontario M2J 5C2
Canada
Phone: +1 416 756 2324 Ext. 321
EMail: smachani@diversinet.com