]> Portable Symmetric Key Container (PSKC) ActivIdentity, Inc.
117 Waterloo Road London SE1 8UL UK +44 (0) 20 7744 6455 Philip.Hoyer@actividentity.com
VeriSign, Inc.
487 E. Middlefield Road Mountain View CA 94043 USA +1 650 426 5173 mpei@verisign.com
Diversinet, Inc.
2225 Sheppard Avenue East Suite 1801 Toronto Ontario M2J 5C2 Canada +1 416 756 2324 Ext. 321 smachani@diversinet.com
keyprov 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.
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 and these elements are also applicable for other time-based algorithms.
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 . 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.
The portable key container is based on an XML schema definition and contains the following main conceptual entities: KeyContainer entity - representing the container that carries the keys Device entity - representing a physical or virtual device where the keys reside optionally bound to a specific user DeviceInfo entity - representing the information about the device and criteria to uniquely identify the device Key entity - representing the key transmitted KeyData entity - representing data related to the key including value either in plain or encrypted shows the high-level structure of the PSKC data elements.
The following sections describe in detail all the entities and related XML schema elements and attributes.
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.
Manufacturer 987654321 Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 ]]>
The attributes of the <KeyContainer> element have the following semantic: 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. 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 . 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.
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: This element indicates the manufacturer of the device. This element contains the serial number of the device. This element describes the model of the device (e.g., one-button-HOTP-token-V1). This element contains the issue number in case devices with the same serial number that are distinguished by different issue numbers. 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. 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.
The following attributes of the <Key> element MUST be included at a minimum: This attribute carries a globally unique identifier for the symmetric key. The identifier is defined as a string of alphanumeric characters. 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 . The <Key> element has a number of optional child elements. An initial set is described below: 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.". A human readable name for the secret key for easier reference. This element serves informational purposes only. This element provides supplementary information for usage with OTP and CR algorithms. A more detailed discussion of the element can be found in . This element carries data about and related to the key. The follow child elements are defined for the <Data> element: This element carries the value of the key itself in a binary representation. This element contains the event counter for event based OTP algorithms. 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) This element carries the time interval value for time based OTP algorithms. 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: The <PlainValue> element carries plaintext content that is typed, for example to xs:integer. 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 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.
The <User> element identifies the user of the device using a distinguished name, as defined in . 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.
The <Usage> element is a child element of the <Key> element and this document defines two child elements: <ChallengeFormat> and <ResponseFormat> The <ChallengeFormat> element defines the characteristics of the challenge in a CR usage scenario whereby the following attributes are defined: This mandatory attribute defines the encoding of the challenge accepted by the device and MUST be one of the following values: Only numerical digits Hexadecimal response All letters and numbers (case sensitive) Base 64 encoded Binary data This optional attribute indicates whether a device needs to check the appended Luhn check digit, as defined in , 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. 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. 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 'BINARY', this value indicates the maximum number of bytes of the unencoded value. 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: 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. This optional attribute indicates whether the device needs to append a Luhn check digit, as defined in , 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. 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.
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 .
Manufacturer 987654321 Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 OTP Issuer MTIzNA== ]]>
This document defines the following elements: 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. 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. 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: The key MUST only be used for OTP generation. The key MUST only be used for Challenge/Response purposes. The key MUST only be used for data encryption purposes. The key MUST only be used to generate a keyed message digest for data integrity or authentication purposes. 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). The key MUST only be used for data decryption purposes. The key MUST only be used for key wrap purposes. The key MUST only be used for key unwrap purposes. The key MUST only be used with a key derivation function to derive a new key (see also Section 8.2.4 of ). 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). 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. The <PINPolicy> element allows policy about the PIN usage to be associated with the key. The following attributes are specified: 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. This mandatory attribute indicates the way the PIN is used during the usage of the key. The following values are defined: This value indicates that the PIN is checked locally on the device before allowing the key to be used in executing the algorithm. This value indicates that the PIN is prepended to the OTP or response hence it MUST be checked by the validation server. This value indicates that the PIN is appended to the OTP or response hence it MUST be checked by the validation server. This value indicates that the PIN is used as part of the algorithm computation. 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. 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. 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. 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.
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
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.
Pre-shared-key http://www.w3.org/2000/09/xmldsig#hmac-sha1 Manufacturer 987654321 Issuer pgznhXdDh4LJ2G3mOY2RL7UA47yizMlXX3ADDcZd8Vs= zdrZbGBj9BDZJzunbfAG3kyZyYc= 0 ]]>
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. 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 is RECOMMENDED. An example list of optionally-to-implement encryption algorithms can be found below:
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:
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: This attribute carries the unique identifier for this key. 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 for more details. The elements of the <DerivedKey> element have the following semantic: This element carries a friendly name of the key. 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. 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 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 . In the example below, the following data is used. qwerty 0x123eff3c4a72129c 1000 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 .
Passphrase1 Ej7/PEpyEpw= 1000 16 TokenVendorAcme 987654321 Example-Issuer oTvo+S22nsmS2Z/RtcoF8Hfh+jzMe0RkiafpoDpnoZTjPYZu6V+A4aEn032yCr4f cOpiQ/H7Zlj6ywiYWtwgz9cRaOA= ]]>
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 the algorithm is set to "http://www.w3.org/2001/04/xmlenc#rsa_1_5".
MIIB5zCCAVCgAwIBAgIESZp/vDANBgkqhkiG9w0BAQUFADA4M Q0wCwYDVQQKEwRJRVRGMRMwEQYDVQQLEwpLZXlQcm92IFdHMRIwEAYDVQQDEwlQU0tDIF Rlc3QwHhcNMDkwMjE3MDkxMzMyWhcNMTEwMjE3MDkxMzMyWjA4MQ0wCwYDVQQKEwRJRVR GMRMwEQYDVQQLEwpLZXlQcm92IFdHMRIwEAYDVQQDEwlQU0tDIFRlc3QwgZ8wDQYJKoZI hvcNAQEBBQADgY0AMIGJAoGBALCWLDa2ItYJ6su80hd1gL4cggQYdyyKK17btt/aS6Q/e DsKjsPyFIODsxeKVV/uA3wLT4jQJM5euKJXkDajzGGOy92+ypfzTX4zDJMkh61SZwlHNJ xBKilAM5aW7C+BQ0RvCxvdYtzx2LTdB+X/KMEBA7uIYxLfXH2Mnub3WIh1AgMBAAEwDQY JKoZIhvcNAQEFBQADgYEAe875m84sYUJ8qPeZ+NG7REgTvlHTmoCdoByU0LBBLotUKuqf rnRuXJRMeZXaaEGmzY1kLonVjQGzjAkU4dJ+RPmiDlYuHLZS41Pg6VMwY+03lhk6I5A/w 4rnqdkmwZX/NgXg06alnc2pBsXWhL4O7nk0S2ZrLMsQZ6HcsXgdmHo= http://www.w3.org/2000/09/xmldsig#hmac-sha1 TokenVendorAcme 987654321 Example-Issuer hJ+fvpoMPMO9BYpK2rdyQYGIxiATYHTHC7e/sPLKYo5/r1v+4 xTYG3gJolCWuVMydJ7Ta0GaiBPHcWa8ctCVYmHKfSz5fdeV5nqbZApe6dofTqhRwZK6 Yx4ufevi91cjN2vBpSxYafvN3c3+xIgk0EnTV4iVPRCR0rBwyfFrPc4= 0 ]]>
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.
<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) . 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).
Manufacturer 987654321 Issuer keyProfile1 MasterKeyLabel 0 OTP ]]> The key value will be derived using the serialnumber and an external key identified by the label 'MasterKeyLabel'.
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 .
TokenVendorAcme 0755225266 Example-Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 j6lwx3rvEPO0vKtMup4NbeVu8nk= j6lwx3rvEPO0vKtMup4NbeVu8nk= CN=Example.com,C=US 12345678 ]]>
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. shows an example utilizing these capabilities.
TokenVendorAcme 654321 Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 2006-05-01T00:00:00Z 2006-05-31T00:00:00Z TokenVendorAcme 123456 Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 2006-05-01T00:00:00Z 2006-05-31T00:00:00Z TokenVendorAcme 9999999 Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 2006-03-01T00:00:00Z 2006-03-31T00:00:00Z Issuer MTIzNDU2Nzg5MDEyMzQ1Njc4OTA= 0 2006-04-01T00:00:00Z 2006-04-30T00:00:00Z ]]>
This section lists a few common extension points provided by PSKC: 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 , and rules for extensibililty are defined in . 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. The XML schema allows new XML attributes to be added where XML extension points have been defined (see "<xs:anyAttribute namespace="##other"/>" in ). This document defines two PSKC algorithm profiles, see . Further PSKC algorithm profiles can be registered as described in . 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. 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 .
HOTP OTP urn:ietf:params:xml:ns:keyprov:pskc#hotp http://www.ietf.org/rfc/rfc4226.txt (this RFC) IESG 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 ) 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 .
KEYPROV-PIN Symmetric static credential comparison urn:ietf:params:xml:ns:keyprov:pskc#pin (this document) (this document) IESG 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 ) MUST be provided. See the example in
This section defines the XML schema for PSKC.
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This specification requests the registration of a new MIME type according to the procedures of RFC 4288 and guidelines in RFC 3023 . application pskc+xml none charset Indicates the character encoding of enclosed XML. Uses XML, which can employ 8-bit characters, depending on the character encoding used. See RFC 3023 , Section 3.2. This content type is designed to carry PSKC protocol payloads. None RFCXXXX [NOTE TO IANA/RFC-EDITOR: Please replace XXXX with the RFC number of this specification.] 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. None .pskcxml 'TEXT' Philip Hoyer, Philip.Hoyer@actividentity.com LIMITED USE This specification is a work item of the IETF KEYPROV working group, with mailing list address <keyprov@ietf.org>. The IESG <iesg@ietf.org>
This section registers an XML schema as per the guidelines in . urn:ietf:params:xml:ns:keyprov:pskc IETF KEYPROV Working Group, Philip Hoyer (Philip.Hoyer@actividentity.com). The XML schema to be registered is contained in . Its first line is
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and its last line is
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This section registers a new XML namespace, "urn:ietf:params:xml:ns:keyprov:pskc", per the guidelines in . urn:ietf:params:xml:ns:keyprov:pskc IETF KEYPROV Working Group, Philip Hoyer (Philip.Hoyer@actividentity.com).
PSKC Namespace

Namespace for PSKC

urn:ietf:params:xml:ns:keyprov:pskc:1.0

See RFCXXXX [NOTE TO IANA/RFC-EDITOR: Please replace XXXX with the RFC number of this specification.].

END ]]>
This specification requests the creation of a new IANA registry for PSKC algorithm profiles in accordance with the principles set out in RFC 5226. As part of this registry IANA will maintain the following information: The name by which the PSKC algorithm profile is generally referred. The type of PSKC algorithm profile registry entry being created, such as encryption, Message Authentication Code (MAC), One Time Password (OTP), Digest. The URN to be used to identify the profile. IANA will be asked to add a pointer to the specification containing information about the PSKC algorithm profile registration. A reference to the stable document in which the algorithm being used with the PSKC is defined. Contact information about the party submitting the registration request. 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. IANA is asked to add an initial value to the registry based on the PSKC HOTP algorithm profile described in .
IANA is requested to create a registry for PSKC version numbers. The registry has the following structure:
Standards action is required to define new versions of PSKC. It is not envisioned to depreciate, delete, or modify existing PSKC versions.
IANA is requested to create a registry for key usage. A description of the 'KeyUsage' element can be found in . The registry has the following structure:
Expert Review is required to define new key usage tokens. Each registration request has to provide a description of the semantic. Using the same procedure it is possible to depreciate, delete, or modify existing key usage tokens.
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.
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 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.
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.
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.
We would like Hannes Tschofenig for his text contributions to this document.
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 , to specify a format that can be freely distributed to the technical community.
PKCS #5: Password-Based Cryptography Standard RSA Laboratories Key words for use in RFCs to Indicate Requirement Levels XML-Signature Syntax and Processing XML Encryption Syntax and Processing. Media Type Specifications and Registration Procedures This document defines procedures for the specification and registration of media types for use in MIME and other Internet protocols. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. XML Media Types The IETF XML Registry This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas. Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names The X.500 Directory uses distinguished names (DNs) as primary keys to entries in the directory. This document defines the string representation used in the Lightweight Directory Access Protocol (LDAP) to transfer distinguished names. The string representation is designed to give a clean representation of commonly used distinguished names, while being able to represent any distinguished name. &I-D.housley-aes-key-wrap-with-pad; NIST Special Publication 800-57, Recommendation for Key Management – Part 1: General (Revised) Guidelines for Writing an IANA Considerations Section in RFCs This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited. Luhn algorithm A a simple checksum formula used to validate a variety of identification numbers as described in U.S. Patent 2,950,048 Chip Authentication Program Functional Architecture MasterCard International Dynamic Symmetric Key Provisioning Protocol HOTP: An HMAC-Based One Time Password Algorithm Initiative for Open AuTHentication
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.
This section describes the use cases related to provisioning the keys using an online provisioning protocol such as .
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 . 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.
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.
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.
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.
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.
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.
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. The format MUST support transport of multiple types of symmetric keys and related attributes for algorithms including HOTP, other OTP, challenge-response, etc. 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 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 The format SHOULD allow bulk representation of symmetric keys The format SHOULD allow bulk representation of PINs related to specific keys The format SHOULD be portable to various platforms. Furthermore, it SHOULD be computationally efficient to process. The format MUST provide appropriate level of security in terms of data encryption and data integrity. For online scenarios the format SHOULD NOT rely on transport level security (e.g., SSL/TLS) for core security requirements. The format SHOULD be extensible. It SHOULD enable extension points allowing vendors to specify additional attributes in the future. 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. 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. The format MUST support the use of pre-shared symmetric keys to ensure confidentiality of sensitive data elements. The format MUST support a password-based encryption (PBE) scheme to ensure security of sensitive data elements. This is a widely used method for various provisioning scenarios. 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.