keyprov P. Hoyer
Internet-Draft ActivIdentity
Intended status: Standards Track M. Pei
Expires: August 26, 2009 VeriSign
S. Machani
Diversinet
February 22, 2009
Portable Symmetric Key Container (PSKC)
draft-ietf-keyprov-pskc-02.txt
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Abstract
This document specifies a symmetric key format for transport and
provisioning of symmetric keys (for example One Time Password (OTP)
shared secrets or symmetric cryptographic keys) to different types of
crypto modules, such as a strong authentication device. The standard
key transport format enables enterprises to deploy best-of-breed
solutions combining components from different vendors into the same
infrastructure.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Portable Key Container Entities Overview and Relationships . . 6
4. <KeyContainer> Element: The Basics . . . . . . . . . . . . . . 8
4.1. <DeviceInfo> Element: Unique Device Identification . . . . 9
4.2. <Key>: Embedding Keying Material . . . . . . . . . . . . . 10
4.3. <User> Element: User Identification . . . . . . . . . . . 11
4.4. <Usage> Element: Supplementary Information for OTP and
CR Algorithms . . . . . . . . . . . . . . . . . . . . . . 12
5. Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6. Protection of Keys and Related Data . . . . . . . . . . . . . 19
6.1. Encryption based on Pre-Shared Keys . . . . . . . . . . . 19
6.2. Encryption based on Passphrase-based Keys . . . . . . . . 22
6.3. Encryption based on Asymmetric Keys . . . . . . . . . . . 24
6.4. Transmission of Key Derivation Values . . . . . . . . . . 26
7. Digital Signature . . . . . . . . . . . . . . . . . . . . . . 28
8. Bulk Provisioning . . . . . . . . . . . . . . . . . . . . . . 30
9. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 33
10. PSKC Algorithm Profile . . . . . . . . . . . . . . . . . . . . 34
10.1. HOTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.2. KEYPROV-PIN . . . . . . . . . . . . . . . . . . . . . . . 34
11. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 36
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
12.1. Content-type registration for 'application/pskc+xml' . . . 43
12.2. XML Schema Registration . . . . . . . . . . . . . . . . . 44
12.3. URN Sub-Namespace Registration . . . . . . . . . . . . . . 44
12.4. PSKC Algorithm Profile Registry . . . . . . . . . . . . . 45
12.5. PSKC Version Registry . . . . . . . . . . . . . . . . . . 46
12.6. Key Usage Registry . . . . . . . . . . . . . . . . . . . . 46
13. Security Considerations . . . . . . . . . . . . . . . . . . . 48
13.1. Payload confidentiality . . . . . . . . . . . . . . . . . 48
13.2. Payload integrity . . . . . . . . . . . . . . . . . . . . 49
13.3. Payload authenticity . . . . . . . . . . . . . . . . . . . 49
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 50
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 51
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16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 52
16.1. Normative References . . . . . . . . . . . . . . . . . . . 52
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 . . . . . . . . . . . . . . . . . . . . 57
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 59
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1. Introduction
With increasing use of symmetric key based authentication systems,
such as those based one time password (OTP) and challenge response
mechanisms, there is a need for vendor interoperability and a
standard format for importing and exporting (provisioning) symmetric
keys. Traditionally, vendors of authentication servers and service
providers have used proprietary formats for importing and exporting
these keys into their systems making it hard to use tokens from
vendor "Foo" with a server from vendor "Bar".
This document proposes a standardized XML-based key container, called
Portable Symmetric Key Container (PSKC), for transporting symmetric
keys and meta data. This document also specifies the information
elements that are required for computing the initial event counter
used by the MAC-Based One Time Password Algorithm (HOTP) algorithm
[HOTP] and these elements are also applicable for other time-based
algorithms.
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2. Terminology
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].
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.
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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 the
keys
2. Device entity - representing a physical or virtual device where
the keys reside optionally bound to a specific user
3. DeviceInfo entity - representing the information about the device
and criteria to uniquely identify the device
4. Key entity - representing the key transmitted
5. KeyData entity - representing data related to the key including
value either in plain or encrypted
Figure 1 shows the high-level structure of the PSKC data elements.
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+---------------+
| KeyContainer |
+---------------+
| EncryptionKey |
| Signature |
| ... |
+---------------+
|
|
/|\ 1..n
+--------------+ +--------------+
| Device | 1| DeviceInfo |
+--------------+-----+--------------+
| User | | SerialNumber |
+--------------+ | Manufacturer |
| | .... |
| +--------------+
/|\ 1..n
+--------------+
| Key |
+--------------+
| ID |
| Algorithm |
| User |
| .... |
+--------------+
|
|
/|\ 1..n +------------+
+--------------+ | Plainvalue |
| KeyData | +----+-------+
+--------------+ |
| name | either|
| value +----------+
| ..... | +------+---------+
+--------------+ | EncryptedValue |
+----------------+
Figure 1
The following sections describe in detail all the entities and
related XML schema elements and attributes.
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4. <KeyContainer> Element: The Basics
In it's most basic form a PSKC document uses the top-level element
<KeyContainer> and a single <Device> element to carry key
information.
The following example shows such a simple PSKC document. We will use
it to describe the structure of the <KeyContainer> element and it's
child elements.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0" id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<Device>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key KeyId="12345678"
KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<Data>
<Secret>
<PlainValue>MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</Device>
</KeyContainer>
Figure 2: Basic PSKC Key Container Example
The attributes of the <KeyContainer> element have the following
semantic:
'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 is
mandatory.
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'ID:' The 'ID' attribute carries a unique identifier for the
container. As such, it helps to identify a specific key
container.
A <KeyContainer> element MUST contain at least one <Device> element.
Multiple <Device> elements can be used when for bulk provisioning,
see Section 8. A <Device> MUST contain at least one <Key> element.
A <Device> MAY be bound to a user. A key SHOULD be bound to only one
<Device> element.
4.1. <DeviceInfo> Element: Unique Device Identification
The <DeviceInfo> element uniquely identifies the device the <Key>
element refers to. 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 criteria to be used.
Combined though the criteria 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.
<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 devices
with the same serial number that are distinguished by different
issue numbers.
<DeviceBinding>: In a number of cases access to lower layer device
identifiers, such as a serial number, from a PSKC implementation
is difficult or not possible. For this purpose an opaque
identifier, carried in the <DeviceBinding> element, is introduced
that allows to bind keys to the device or to a class of devices.
When loading keys into a device, the value of the <DeviceBinding>
element MUST be checked against information provided to the user
via out-of-band mechanisms. The implementation then ensures that
the correct device or class of device is being used with respect
to the provisioned key.
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<StartDate>: and <ExpiryDate>: These two elements indicates 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 in UTC form with no timezone component.
Implementations SHOULD NOT rely on time resolution finer than
milliseconds and MUST NOT generate time instants that specify leap
seconds.
Depending on the device type certain child elements of the
<DeviceInfo> element are necessary to include 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.
4.2. <Key>: Embedding Keying Material
The following attributes of the <Key> element MUST be included at a
minimum:
'KeyId': This attribute carries a globally unique identifier for the
symmetric key. The identifier is defined as a string of
alphanumeric characters.
'KeyAlgorithm': This attribute contains a unique identifier for the
PSKC algorithm profile. This profile associates a specific
semantic to the elements and attributes contained in the <Key>
element. More information about the PSKC algorithm profile
defined in this document can be found in Section 10.
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.
<Usage>: This element provides supplementary information for usage
with OTP and CR algorithms. A more detailed discussion of the
element can be found in Section 4.4.
<Data>: This element carries data about and related to the key. The
follow child elements are defined for the <Data> element:
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<Secret>: This element carries the value of the key itself in a
binary representation.
<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 interval is used, this element carries
the number of time intervals passed from a specific start
point, normally algorithm dependent)
<TimeInterval>: This element carries the time interval value for
time based OTP algorithms.
<TimeDrift>: This element contains the device clock drift value
for time based OTP algorithms. The value indicates number of
seconds that the device clock may drift each day.
All these elements listed above (and those defined in the future)
obey a simple structure in that they MUST support child elements
to convey the content in plaintext and in encrypted format:
Plain Text: The <PlainValue> element carries plaintext content
that is typed, for example to xs:integer.
Encrypted Content: The <EncryptedValue> element carries encrypted
content.
Additionally, a <ValueMac> element, which is populated with a MAC
generated from the unencrypted value in case the encryption
algorithm does not support integrity checks, MAY be included as a
child element. The example shown at Figure 2 illustrates the
usage of the <Data> element with two child elements, namely
<Secret> and <Counter>. Both elements carry plaintext value
within the <PlainValue> child element.
4.3. <User> Element: User Identification
The <User> element identifies the user of the device using a
distinguished name, as defined in [RFC4514]. For example:
UID=jsmith,DC=example,DC=net
There is no semantic 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.
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4.4. <Usage> Element: Supplementary Information for OTP and CR
Algorithms
The <Usage> element is a child element of the <Key> element and this
document defines two child elements: <ChallengeFormat> and
<ResponseFormat>
<ChallengeFormat>:
The <ChallengeFormat> element defines the characteristics of the
challenge in a CR usage scenario whereby the following attributes
are defined:
'Encoding': This mandatory attribute 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
BINARY Binary data
'CheckDigit': This optional attribute indicates whether a device
needs to check the appended Luhn check digit, as defined in
[LUHN], contained in a provided challenge. This is only valid
if the 'Encoding' attribute is 'DECIMAL'. A value of TRUE
indicates that the device will check the appended Luhn check
digit in a provided challenge. A value of indicates that the
device will not check appended Luhn check digit in challenge.
'Min': This mandatory attribute defines the minimum size of the
challenge accepted by the device for CR mode. If the
'Encoding' attribute is 'DECIMAL', 'HEXADECIMAL' or
'ALPHANUMERIC' this value indicates the minimum number of
digits/characters. If the 'Encoding' attribute is 'BASE64' or
'BINARY', this value indicates the minimum number of bytes of
the unencoded value.
'Max': This mandatory attribute defines the maximum size of the
challenge accepted by the device for CR mode. If the
'Encoding' attribute is 'DECIMAL', 'HEXADECIMAL' or
'ALPHANUMERIC' this value indicates the maximum number of
digits/characters. If the 'Encoding' attribute is 'BASE64' or
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'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 where 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 mandatory attribute defines the encoding of the
response generated by the device and MUST be one of the
following values: DECIMAL, HEXADECIMAL, ALPHANUMERIC, BASE64,
or BINARY.
'CheckDigit': This optional attribute indicates whether the
device needs to append a Luhn check digit, as defined in
[LUHN], to the response. This is only valid if the 'Encoding'
attribute is '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 mandatory attribute defines the length of the
response generated by the device. If the 'Encoding' attribute
is 'DECIMAL', 'HEXADECIMAL' or 'ALPHANUMERIC' this value
indicates the number of digits/characters. If the 'Encoding'
attribute is 'BASE64' or 'BINARY', this value indicates the
number of bytes of the unencoded value.
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5. Policy
This section illustrates the functionality of the <Policy> element
within PSKC that allows policy to be attached to a key and related
meta data. 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 extension does not lead to unintended key usage.
We will start our description with an example that expands the
example shown in Figure 3.
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<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1.0" id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<Device>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key KeyId="12345678"
KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<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>
<Key KeyId="123456781"
KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#pin">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="4" Encoding="DECIMAL"/>
</Usage>
<Data>
<Secret>
<PlainValue>MTIzNA==</PlainValue>
</Secret>
</Data>
</Key>
</Device>
</KeyContainer>
Figure 3: Non-Encrypted HOTP Secret Key protected by PIN
This document defines the following elements:
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<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 value MUST be
expressed in UTC form, with no time zone component.
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 then the current time is
assumed as a start time.
<NumberOfTransactions>: The value in this element indicates a
restriction regarding the number of times a key carried within the
PSKC document can be applied. When this element is omitted then
there is no restriction regarding the number of times a key is
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.
Unlock: The key MUST only be used for an inverse challenge
response in the case 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 [NIST]).
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[NIST]).
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Verify: The key MUST only be used to verify the digest or
signatures ( is the vice verso of Integrity)
The element MAY also be repeated to allow several key usages to be
expressed. When this element is absent then 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 contains the unique key id of the key
held within this container 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
OTP or response hence it MUST be checked by the validation
server.
Append: This value indicates that the PIN is appended to the
OTP or response hence it MUST be checked by the validation
server.
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 can be entered wrongly before it MUST NOT be
possible to use the key anymore.
'MinLength': This attribute indicates the minimum length of a PIN
that can be set to protect this key. It MUST NOT be possible
to set a PIN shorter than this value. If the 'PINFormat'
attribute is 'DECIMAL', 'HEXADECIMAL' or 'ALPHANUMERIC' this
value indicates the number of digits/characters. If the
'PINFormat' attribute is 'BASE64' or 'BINARY', this value
indicates the number of bytes of the unencoded value.
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'MaxLength': This attribute indicates the maximum lenght 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 'DECIMAL', 'HEXADECIMAL' or 'ALPHANUMERIC' this
value indicates the number of digits/characters. If the
'PINFormat' attribute is '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' attribute, otherwise it
MUST be enforced on the server side.
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6. Protection of Keys and Related Data
With the functionality described in the previous sections information
related to keys had to be transmitted in clear text. 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 elements. Key encryption is supported based on the
following credentials: pre-shared keys, passphrase-based keys, and
asymmetric keys
6.1. Encryption based on Pre-Shared Keys
Figure 4 shows an example that illustrates the encryption of the
content of the <Secret> element using AES128-CBC, the plaintext value
of <Secret> is '3132333435363738393031323334353637383930'. The name
of the pre-shared secret is "Example-Key1", as set in the <KeyName>
element (which is a child element of the <EncryptionKey> element).
The value of the key used is '12345678901234567890123456789012'.
Since AES128-CBC does not provide integrity checks a keyed MAC is
applied to the encrypted value using the algorithm indicated in
<MACAlgorithm> element (in our example
"http://www.w3.org/2000/09/xmldsig#hmac-sha1" is used). The result
of the keyed MAC computation is placed in the <ValueMAC> element.
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<?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>
<MACAlgorithm>http://www.w3.org/2000/09/xmldsig#hmac-sha1
</MACAlgorithm>
<Device>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key KeyId="12345678"
KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<Data>
<Secret>
<EncryptedValue>
<xenc:EncryptionMethod
Algorithm=
"http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
<xenc:CipherData>
<xenc:CipherValue>
pgznhXdDh4LJ2G3mOY2RL7UA47yizMlXX3ADDcZd8Vs=
</xenc:CipherValue>
</xenc:CipherData>
</EncryptedValue>
<ValueMAC>zdrZbGBj9BDZJzunbfAG3kyZyYc=
</ValueMAC>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</Device>
</KeyContainer>
Figure 4: AES-128-CBC Encrypted Pre-Shared Secret Key
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.
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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. Hence, if keys of a different length have to be protected
then the usage of the key wrap algorithm with padding, as described
in [I-D.housley-aes-key-wrap-with-pad] is RECOMMENDED. An example
list of optionally-to-implement encryption algorithms can be found
below:
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
When algorithms without integrity checks are used, such as AES-128-
CBC, a keyed MAC value using the same key as the key encryption key
MUST be placed in the <ValueMAC> element of the <Data> element. In
this case the MAC algorithm type MUST be set in the <MACAlgorithm>
element of the <KeyContainer> element. Implementations of PSKC MUST
support HMAC-SHA1 (with the URI of
http://www.w3.org/2000/09/xmldsig#hmac-sha1) as the mandatory-to-
implement MAC algorithm. An example list of optionally-to-implement
MAC algorithms can be found below:
Algorithm | Uniform Resource Locator (URL)
---------------+-----------------------------------------------------
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
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6.2. Encryption based on Passphrase-based Keys
To be able to support passphrase based key encryption keys as defined
in PKCS#5 the following PBE related parameters have been introduced
into PSKC. Implementations of PSKC MUST support the PKCS#5
recommended PBKDF2 and PBES2 algorithms. Differing from the PKCS#5
XML schema definition, the PBKDF2 and PBES2 are specified in two
separate elements in a <KeyContainer> element:
(a) PBKDF2 is specified via the <DerivedKey> element, which is a
child element of the <EncryptionKey> element.
(b) PBES2 is specified by the 'Algorithm' attribute (with the
value set to
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2) of
the <EncryptionMethod> element used inside the encrypted data
elements.
The attributes of the <DerivedKey> element have the following
semantic:
'xml:id': This attribute carries the unique identifier for this key.
'Type': This attribute was included for conformance with XML
encryption. It is an optional attribute identifying type
information about the plaintext form of the encrypted content.
Please see Section 3.1 of [XMLENC] for more details.
The elements of the <DerivedKey> element have the following semantic:
<CarriedKeyName>: This element carries a friendly name of the key.
<KeyDerivationMethod>: This element defines how key encryption key
is derived. The 'Algorithm' attribute is used to indicate the key
derivation method. When PBKDF2 is used, the URI
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbkdf2 MUST
be used. When PBKDF2 is used, it MUST include the <PBKDF2-params>
child element to indicate the PBKDF2 parameters, such as salt and
iteration count.
<ReferenceList>: This element contains a list of IDs of the elements
that have been encrypted by this key.
When PBES2 is used for encryption, the URL
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2 MUST be
specified as the 'Algorithm' attribute of <xenc:EncryptionMethod>
element. The underlying encryption scheme and initialization vector
MUST be expressed in the <pskc:EncryptionScheme> element, which is a
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child element of <xenc:EncryptionMethod>.
When PKCS#5 password based encryption is used, the <EncryptionKey>
element and <xenc:EncryptionMethod> element MUST be used in exactly
the form as shown in Figure 5.
In the example below, the following data is used.
Password: qwerty
Salt: 0x123eff3c4a72129c
Iteration Count: 1000
OTP Secret: 12345678901234567890
The derived encryption key is "0x651e63cd57008476af1ff6422cd02e41".
This key is also used to calculate MAC value of the secret key
"12345678901234567890". The encryption with algorithm "AES-128-CBC"
follows the specification defined in [XMLENC].
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer
xmlns="urn:ietf:params:xml:ns:keyprov:pskc"
xmlns:pkcs5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
Version="1.0">
<EncryptionKey>
<DerivedKey>
<CarriedKeyName>Passphrase1</CarriedKeyName>
<KeyDerivationMethod
Algorithm=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#pbkdf2">
<pkcs5:PBKDF2-params>
<pkcs5:Salt>
<pkcs5:Specified>Ej7/PEpyEpw=</pkcs5:Specified>
</pkcs5:Salt>
<pkcs5:IterationCount>1000</pkcs5:IterationCount>
<pkcs5:KeyLength>16</pkcs5:KeyLength>
<pkcs5:PRF/>
</pkcs5:PBKDF2-params>
</KeyDerivationMethod>
<xenc:ReferenceList>
<xenc:DataReference URI="#ED"/>
</xenc:ReferenceList>
</DerivedKey>
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</EncryptionKey>
<Device>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp"
KeyId="123456">
<Issuer>Example-Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<Data>
<Secret>
<EncryptedValue Id="ED">
<xenc:EncryptionMethod Algorithm=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2">
<EncryptionScheme Algorithm=
"http://www.w3.org/2001/04/xmlenc#aes128-cbc">
</EncryptionScheme>
</xenc:EncryptionMethod>
<xenc:CipherData>
<xenc:CipherValue>
oTvo+S22nsmS2Z/RtcoF8Hfh+jzMe0RkiafpoDpnoZTjPYZu6V+A4aEn032yCr4f
</xenc:CipherValue>
</xenc:CipherData>
<ns2:ValueMAC>cOpiQ/H7Zlj6ywiYWtwgz9cRaOA=
</ns2:ValueMAC>
</EncryptedValue>
</Secret>
</Data>
</Key>
</Device>
</KeyContainer>
Figure 5: 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 6 the algorithm is set to
"http://www.w3.org/2001/04/xmlenc#rsa_1_5".
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<?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"
Version="1.0">
<EncryptionKey>
<ds:X509Data>
<ds:X509Certificate>MIIB5zCCAVCgAwIBAgIESZp/vDANBgkqhkiG9w0BAQUFADA4M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</ds:X509Certificate>
</ds:X509Data>
</EncryptionKey>
<MACAlgorithm>
http://www.w3.org/2000/09/xmldsig#hmac-sha1
</MACAlgorithm>
<Device>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key
KeyId="MBK000000001"
KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp">
<Issuer>Example-Issuer</Issuer>
<Usage>
<ResponseFormat Length="6" Encoding="DECIMAL"/>
</Usage>
<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>
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</EncryptedValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</Device>
</KeyContainer>
Figure 6: Example of a PSKC Document using Encryption based on
Asymmetric Keys
Systems implementing PSKC MUST support the
http://www.w3.org/2001/04/xmlenc#rsa-1_5 algorithm.
http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p is an example of an
optional-to-implement algorithm.
6.4. 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 party to establish a set of key attribute values that are
not transmitted within the container but agreed between the two
parties out of band. This element will then represent the unique
reference to a set of attribute values. For example, a smart card
application personalisation profile id related to attributes present
on a smart card application that have influence when computing a
response. The sending and the receiving party would agree to a set
of values related to the MasterCard's Chip Authentication Protocol
(CAP) [CAP].
For example, sending and receiving party would agree that
KeyProfileId='1' would represent a certain set of values (e.g.,
Internet authentication flag set to a specific value). When sending
keys these values would not be transmitted as key attributes but only
referred to via the <KeyProfileId> element set to the specific agreed
profile (in this case '1'). When the receiving party receives the
keys it can then associate all relevant key attributes contained in
the out of band agreed profile with the imported keys. Often this
methodology is used between the manufacturing and the validation
service to avoid transmission of mainly the same set of values.
The <KeyReference> element contains a reference to an external key
when key derivation schemes are used and no specific key is
transported but only the reference to the external key is used (e.g.,
the PKCS#11 key label).
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<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1" id="exampleID1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<Device>
<DeviceInfo>
<Manufacturer>Manufacturer</Manufacturer>
<SerialNo>987654321</SerialNo>
</DeviceInfo>
<Key KeyId="12345678"
KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<KeyProfileId>keyProfile1</KeyProfileId>
<KeyReference>MasterKeyLabel</KeyReference>
<Data>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
<Policy>
<KeyUsage>OTP</KeyUsage>
</Policy>
</Key>
</Device>
</KeyContainer>
The key value will be derived using the serialnumber and an external
key identified by the label 'MasterKeyLabel'.
Figure 7: Example of a PSKC Document transmitting a HOTP key via key
derivation values
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7. Digital Signature
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:pkcs5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
Version="1">
<Device>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>0755225266</SerialNo>
</DeviceInfo>
<Key KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp"
KeyId="123">
<Issuer>Example-Issuer</Issuer>
<Usage>
<ResponseFormat Length="6" Encoding="DECIMAL"/>
</Usage>
<Data>
<Secret>
<PlainValue>
MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
</PlainValue>
</Secret>
<Counter>
<PlainValue>0</PlainValue>
</Counter>
</Data>
</Key>
</Device>
<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>
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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 8: Digital Signature Example
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8. Bulk Provisioning
The functionality of bulk provisioning can be accomplished by
repeating the <Device> element multiple times within the
<KeyContainer> element indicating that multiple keys are provided to
different devices. The <EncryptionKey> element then applies to all
<Device> elements. Furthermore, within a single <Device> element the
<Key> element may also be repeated providing different keys and meta
data for a single device.
Figure 9 shows an example utilizing these capabilities.
<?xml version="1.0" encoding="UTF-8"?>
<KeyContainer Version="1"
xmlns="urn:ietf:params:xml:ns:keyprov:pskc">
<Device>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>654321</SerialNo>
</DeviceInfo>
<Key KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp"
KeyId="1">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<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>
</Device>
<Device>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>123456</SerialNo>
</DeviceInfo>
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<Key KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp"
KeyId="2">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<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>
</Device>
<Device>
<DeviceInfo>
<Manufacturer>TokenVendorAcme</Manufacturer>
<SerialNo>9999999</SerialNo>
</DeviceInfo>
<Key KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp"
KeyId="3">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<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>
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<Key KeyAlgorithm="urn:ietf:params:xml:ns:keyprov:pskc#hotp"
KeyId="4">
<Issuer>Issuer</Issuer>
<Usage>
<ResponseFormat Length="8" Encoding="DECIMAL"/>
</Usage>
<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>
</Device>
</KeyContainer>
Figure 9: Bulk Provisioning Example
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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 then a new version number has to be allocated to
refer to the new specification version. The version number is
carried inside the 'Algorithm' attribute, as described in
Section 4, and rules for extensibililty 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
of type of XML elements 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. 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. The usage of 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 to restrict the usage of the key to certain functions, such
as "OTP usage only". Further values may be registered as
described in Section 12.
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10. PSKC Algorithm Profile
10.1. HOTP
Common Name: HOTP
Class: OTP
URN: urn:ietf:params:xml:ns:keyprov:pskc#hotp
Algorithm Definition: http://www.ietf.org/rfc/rfc4226.txt
Identifier Definition: (this RFC)
Registrant Contact: IESG
Profiling:
The <Usage> element MUST be present. The <ResponseFormat>
element of the <Usage> element MUST be used to indicate the OTP
length and the value format.
The <Counter> element (see Section 4.2) MUST be provided as
meta-data 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.
+ The <PINPolicy> element MAY be present but the
'PINUsageMode' attribute cannot be set to "Algorithmic".
An example can be found in Figure 2.
10.2. KEYPROV-PIN
Common Name: KEYPROV-PIN
Class: Symmetric static credential comparison
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URN: urn:ietf:params:xml:ns:keyprov:pskc#pin
Algorithm Definition: (this document)
Identifier Definition (this document)
Registrant Contact: IESG
Profiling:
The <Usage> element MAY be present but no attribute of the
<Usage> element is required. The <ResponseFormat> element MAY
be used to indicate the PIN value format.
The <Secret> element (see Section 4.2) MUST be provided.
See the example in Figure 3
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11. XML Schema
This section defines the XML schema for PSKC.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:keyprov:pskc"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:pskc="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#"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
schemaLocation=
"http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/
xmldsig-core-schema.xsd"/>
<xs:import namespace="http://www.w3.org/2001/04/xmlenc#"
schemaLocation=
"http://www.w3.org/TR/2002/REC-xmlenc-core-20021210/
xenc-schema.xsd"/>
<xs:import namespace="http://www.w3.org/XML/1998/namespace"/>
<xs:complexType name="KeyContainerType">
<xs:sequence>
<xs:element name="EncryptionKey" type="ds:KeyInfoType"
minOccurs="0"/>
<xs:element name="MACAlgorithm" type="pskc:KeyAlgorithmType"
minOccurs="0"/>
<xs:element name="Device" type="pskc:DeviceType"
minOccurs="1" maxOccurs="unbounded"/>
<xs:element name="Signature" type="ds:SignatureType"
minOccurs="0"/>
<xs:element name="Extensions"
type="pskc:ExtensionsType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="Version" type="pskc:VersionType"
use="required"/>
<xs:attribute name="id" type="xs:ID" use="optional"/>
</xs:complexType>
<xs:simpleType name="VersionType" final="restriction">
<xs:restriction base="xs:string">
<xs:pattern value="\d{1,2}\.\d{1,3}"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="KeyType">
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<xs:sequence>
<xs:element name="Issuer"
type="xs:string" minOccurs="0"/>
<xs:element name="Usage"
type="pskc:UsageType"/>
<xs:element name="KeyProfileId"
type="xs:string" minOccurs="0"/>
<xs:element name="KeyReference"
type="xs:string" minOccurs="0"/>
<xs:element name="FriendlyName"
type="xs:string" minOccurs="0"/>
<xs:element name="Data" type="pskc:KeyDataType"
minOccurs="0" maxOccurs="1"/>
<xs:element name="UserId" type="xs:string"
minOccurs="0"/>
<xs:element name="Policy"
type="pskc:PolicyType" minOccurs="0"/>
<xs:element name="Extensions"
type="pskc:ExtensionsType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="KeyId"
type="xs:string" use="required"/>
<xs:attribute name="KeyAlgorithm"
type="pskc:KeyAlgorithmType"
use="optional"/>
<xs:attribute name="KeyProperties"
type="xs:IDREF" use="optional"/>
</xs:complexType>
<xs:complexType name="PolicyType">
<xs:sequence>
<xs:element name="StartDate"
type="xs:dateTime" minOccurs="0"/>
<xs:element name="ExpiryDate"
type="xs:dateTime" minOccurs="0"/>
<xs:element name="PINPolicy"
type="pskc:PINPolicyType" minOccurs="0"/>
<xs:element name="KeyUsage"
type="pskc:KeyUsageType" minOccurs="0"/>
<xs:element name="NumberOfTransactions"
type="xs:nonNegativeInteger" minOccurs="0"/>
<xs:any namespace="##other"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="KeyDataType">
<xs:sequence>
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<xs:element name="Secret"
type="pskc:binaryDataType"
minOccurs="0" maxOccurs="1"/>
<xs:element name="Counter"
type="pskc:longDataType"
minOccurs="0" maxOccurs="1"/>
<xs:element name="Time"
type="pskc:intDataType"
minOccurs="0" maxOccurs="1"/>
<xs:element name="TimeInterval"
type="pskc:intDataType"
minOccurs="0" maxOccurs="1"/>
<xs:element name="TimeDrift"
type="pskc:intDataType"
minOccurs="0" maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="binaryDataType">
<xs:sequence>
<xs:choice>
<xs:element name="PlainValue"
type="xs:base64Binary"/>
<xs:element name="EncryptedValue"
type="xenc:EncryptedDataType"/>
</xs:choice>
<xs:element name="ValueMAC"
type="xs:base64Binary" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="intDataType">
<xs:sequence>
<xs:choice>
<xs:element name="PlainValue"
type="xs:int"/>
<xs:element name="EncryptedValue"
type="xenc:EncryptedDataType"/>
</xs:choice>
<xs:element name="ValueMAC"
type="xs:base64Binary" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="stringDataType">
<xs:sequence>
<xs:choice>
<xs:element name="PlainValue"
type="xs:string"/>
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<xs:element name="EncryptedValue"
type="xenc:EncryptedDataType"/>
</xs:choice>
<xs:element name="ValueMAC"
type="xs:base64Binary" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="longDataType">
<xs:sequence>
<xs:choice>
<xs:element name="PlainValue"
type="xs:long"/>
<xs:element name="EncryptedValue"
type="xenc:EncryptedDataType"/>
</xs:choice>
<xs:element name="ValueMAC"
type="xs:base64Binary" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="DerivedKeyType">
<xs:sequence>
<xs:element name="KeyDerivationMethod"
type="pskc:KeyDerivationMethodType" minOccurs="0"/>
<xs:element ref="xenc:ReferenceList" minOccurs="0"/>
<xs:element name="CarriedKeyName" type="xs:string"
minOccurs="0"/>
</xs:sequence>
<xs:attribute name="id" type="xs:ID" use="optional"/>
<xs:attribute name="Type" type="xs:anyURI" use="optional"/>
</xs:complexType>
<xs:complexType name="KeyDerivationMethodType">
<xs:sequence>
<xs:any namespace="##other" processContents="lax"
minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="Algorithm" type="xs:anyURI"
use="required"/>
</xs:complexType>
<xs:complexType name="PINPolicyType">
<xs:attribute name="PINKeyId" type="xs:string"
use="optional"/>
<xs:attribute name="PINUsageMode"
type="pskc:PINUsageModeType"/>
<xs:attribute name="MaxFailedAttempts" type="xs:unsignedInt"
use="optional"/>
<xs:attribute name="MinLength"
type="xs:unsignedInt" use="optional"/>
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<xs:attribute name="MaxLength"
type="xs:unsignedInt" use="optional"/>
<xs:attribute name="PINEncoding"
type="pskc:ValueFormatType" use="optional"/>
<xs:anyAttribute namespace="##other"/>
</xs:complexType>
<xs:simpleType name="PINUsageModeType">
<xs:restriction base="xs:string">
<xs:enumeration value="Local"/>
<xs:enumeration value="Prepend"/>
<xs:enumeration value="Append"/>
<xs:enumeration value="Algorithmic"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="KeyUsageType">
<xs:restriction base="xs:string">
<xs:enumeration value="OTP"/>
<xs:enumeration value="CR"/>
<xs:enumeration value="Encrypt"/>
<xs:enumeration value="Integrity"/>
<xs:enumeration value="Unlock"/>
<xs:enumeration value="Decrypt"/>
<xs:enumeration value="KeyWrap"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="DeviceInfoType">
<xs:sequence>
<xs:element name="Manufacturer" type="xs:string"
minOccurs="0"/>
<xs:element name="SerialNo" type="xs:string"
minOccurs="0"/>
<xs:element name="Model" type="xs:string"
minOccurs="0"/>
<xs:element name="IssueNo" type="xs:string"
minOccurs="0"/>
<xs:element name="DeviceBinding" type="xs:string"
minOccurs="0"/>
<xs:element name="StartDate" type="xs:dateTime"
minOccurs="0"/>
<xs:element name="ExpiryDate" type="xs:dateTime"
minOccurs="0"/>
<xs:element name="Extensions"
type="pskc:ExtensionsType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="DeviceType">
<xs:sequence>
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<xs:element name="DeviceInfo" type="pskc:DeviceInfoType"
minOccurs="0"/>
<xs:element name="Key" type="pskc:KeyType"
maxOccurs="unbounded"/>
<xs:element name="User" type="xs:string"
minOccurs="0"/>
<xs:element name="Extensions"
type="pskc:ExtensionsType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="UsageType">
<xs:choice>
<xs:element name="ChallengeFormat" minOccurs="0">
<xs:complexType>
<xs:attribute name="Encoding"
type="pskc:ValueFormatType" use="required"/>
<xs:attribute name="Min" type="xs:unsignedInt"
use="required"/>
<xs:attribute name="Max" type="xs:unsignedInt"
use="required"/>
<xs:attribute name="CheckDigits" type="xs:boolean"
default="false"/>
</xs:complexType>
</xs:element>
<xs:element name="ResponseFormat" minOccurs="0">
<xs:complexType>
<xs:attribute name="Encoding"
type="pskc:ValueFormatType" use="required"/>
<xs:attribute name="Length" type="xs:unsignedInt"
use="required"/>
<xs:attribute name="CheckDigits" type="xs:boolean"
default="false"/>
</xs:complexType>
</xs:element>
<xs:element name="Extensions"
type="pskc:ExtensionsType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:choice>
</xs:complexType>
<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>
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<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:element name="DerivedKey" type="pskc:DerivedKeyType"/>
<xs:element name="EncryptionScheme"
type="xenc:EncryptionMethodType"/>
<xs:element name="KeyContainer" type="pskc:KeyContainerType"/>
</xs:schema>
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12. IANA Considerations
12.1. Content-type registration for 'application/pskc+xml'
This specification requests the registration of a new MIME 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
Mandatory parameters: none
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: This content type is designed to carry PSKC
protocol payloads.
Interoperability considerations: None
Published specification: RFCXXXX [NOTE TO IANA/RFC-EDITOR: Please
replace XXXX with the RFC number of this specification.]
Applications which use this media type: This MIME 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'
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Personal and email address for further information: Philip Hoyer,
Philip.Hoyer@actividentity.com
Intended usage: LIMITED USE
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:ns: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:
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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:1.0</h2>
<p>See <a href="[URL of published RFC]">RFCXXXX
[NOTE TO IANA/RFC-EDITOR:
Please replace XXXX with the RFC number of this
specification.]</a>.</p>
</body>
</html>
END
12.4. PSKC Algorithm Profile Registry
This specification requests the creation of a new IANA registry for
PSKC algorithm profiles in accordance with the principles set out in
RFC 5226 [RFC5226].
As part of this registry IANA will maintain 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.
URN: The URN to be used to identify the profile.
Identifier Definition: IANA will be asked to 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.
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Registrant Contact: Contact information about the party submitting
the registration request.
PSKC Profiling: Information about PSKC XML elements and attributes
being used (or not used) with this specific profile of PSKC.
PSKC algorithm profile identifier registrations are to be subject to
Expert Review as per RFC 5226 [RFC5226].
IANA is asked to add an initial value to the registry based on the
PSKC HOTP algorithm profile described in Section 10.
12.5. PSKC Version Registry
IANA is requested to create a registry for PSKC version numbers. The
registry has the following structure:
PSKC Version | Specification
+---------------------------+----------------
| 1 | [This document]
Standards action is required to define new versions of PSKC. It is
not envisioned to depreciate, delete, or modify existing PSKC
versions.
12.6. Key Usage Registry
IANA is requested to create a registry for key usage. A description
of the 'KeyUsage' element can be found in Section 5. The registry
has the following structure:
Key Usage Token | Specification
+---------------------------+-------------------------------
| OTP | [Section 5 of this document]
| CR | [Section 5 of this document]
| Encrypt | [Section 5 of this document]
| Integrity | [Section 5 of this document]
| Unlock | [Section 5 of this document]
| Decrypt | [Section 5 of this document]
| KeyWrap | [Section 5 of this document]
| Unwrap | [Section 5 of this document]
| Derive | [Section 5 of this document]
| Generate | [Section 5 of this document]
| Verify | [Section 5 of this document]
+---------------------------+-------------------------------
Expert Review is required to define new key usage tokens. Each
registration request has to provide a description of the semantic.
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Using the same procedure it is possible to depreciate, delete, or
modify existing key usage tokens.
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13. Security Considerations
The portable key container 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. Payload 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 payload encryption. Symmetric
cryptographic cipher should be used - the longer the cryptographic
key, the stronger the protection. At the time of this writing both
3DES and AES are mandatory algorithms but 3DES may be dropped in the
relatively near future. Applications concerned with algorithm
longevity are advised to use AES-256-CBC. In cases where the
exchange of key encryption keys between the sender and the receiver
is not possible, asymmetric encryption of the secret key payload may
be employed. Similarly to symmetric key cryptography, the stronger
the asymmetric key, the more secure the protection is.
If the payload is encrypted with a method that uses one of the
password-based encryption methods provided above, the 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.
Practical implementations should use PBESalt and PBEIterationCount
when PBE encryption is used. Different PBESalt value per key
container should be used for best protection.
The second approach to protecting the confidentiality of the payload
is based on using transport layer security. The secure channel
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 transport
the messages that travel across. No payload encryption is required
in this mode. Secure channels that encrypt and digest each message
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provide an extra measure of security, especially when the signature
of the payload does not encompass the entire payload.
Because of the fact that the plain text payload is protected only by
the transport layer security, practical implementation must ensure
protection against man-in-the-middle attacks. Validating the secure
channel end-points is critically important for eliminating intruders
that may compromise the confidentiality of the payload.
13.2. Payload integrity
The portable symmetric key container provides a mean to guarantee the
integrity of the information it contains through digital signatures.
For best security practices, the digital signature of the container
should encompass the entire payload. This provides assurances for
the integrity of all attributes. It also allows verification of the
integrity of a given payload 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. Payload authenticity
The digital signature of the payload is the primary way of showing
its authenticity. The recipient of the container may use the public
key associated with the signature to assert the authenticity of the
sender by tracing it back to a preloaded public key or certificate.
Note that the digital signature of the payload can be checked even
after the container has been delivered through the secure channel of
communication.
A weaker payload authenticity guarantee may be provided by the
transport layer if it is configured to digest each message it
transports. However, no authenticity verification is possible once
the container is delivered at the recipient end. This approach may
be useful in cases where the digital signature of the container does
not encompass the entire payload.
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14. Contributors
We would like Hannes Tschofenig for his text contributions to this
document.
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15. Acknowledgements
The authors of this draft would like to thank the following people
for their feedback: Apostol Vassilev, Shuh Chang, Jon Martinson,
Siddhart Bajaj, Stu Veath, 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 draft 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.
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16. References
16.1. Normative References
[PKCS5] RSA Laboratories, "PKCS #5: Password-Based Cryptography
Standard", Version 2.0,
URL: http://www.rsasecurity.com/rsalabs/pkcs/, March 1999.
[RFC2119] "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.
[XMLDSIG] Eastlake, D., "XML-Signature Syntax and Processing",
URL: http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/,
W3C Recommendation, February 2002.
[XMLENC] Eastlake, D., "XML Encryption Syntax and Processing.",
URL: http://www.w3.org/TR/xmlenc-core/,
W3C Recommendation, December 2002.
16.2. Informative References
[CAP] MasterCard International, "Chip Authentication Program
Functional Architecture", September 2004.
[DSKPP] Doherty, A., Pei, M., Machani, S., and M. Nystrom,
"Dynamic Symmetric Key Provisioning Protocol", Internet
Draft Informational, URL: http://www.ietf.org/
internet-drafts/draft-ietf-keyprov-dskpp-05.txt,
February 2008.
[HOTP] MRaihi, D., Bellare, M., Hoornaert, F., Naccache, D., and
O. Ranen, "HOTP: An HMAC-Based One Time Password
Algorithm", RFC 4226, December 2005.
[I-D.housley-aes-key-wrap-with-pad]
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Housley, R. and M. Dworkin, "Advanced Encryption Standard
(AES) Key Wrap Algorithm with Padding",
draft-housley-aes-key-wrap-with-pad-00 (work in progress),
January 2009.
[LUHN] Luhn, H., "Luhn algorithm", US Patent 2950048,
August 1960, <http://patft.uspto.gov/netacgi/
nph-Parser?patentnumber=2950048>.
[NIST] 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",
URL: http://www.openauthentication.org.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
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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 such as [DSKPP].
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 such as [DSKPP]. 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 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.
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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. 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-Aire (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 end-user's mobile
phone.
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.
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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.
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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 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 such as [DSKPP]
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 appropriate level of security in terms
of data encryption and data integrity.
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R8: For online scenarios the format SHOULD NOT rely on transport
level security (e.g., 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 lifecycle 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.
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Authors' Addresses
Philip Hoyer
ActivIdentity, Inc.
117 Waterloo Road
London, SE1 8UL
UK
Phone: +44 (0) 20 7744 6455
Email: Philip.Hoyer@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
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