Network Working Group J. Salowey Internet-Draft Cisco Systems Expires: July 15, 2007 L. Dondeti V. Narayanan Qualcomm, Inc M. Nakhjiri Huawei USA January 11, 2007 Specification for the Derivation of Usage Specific Root Keys (USRK) from an Extended Master Session Key (EMSK) draft-ietf-hokey-emsk-hierarchy-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 15, 2007. Copyright Notice Copyright (C) The Internet Society (2007). Abstract An Extended Master Session Key (EMSK) is a cryptographic key generated from an Extensible Authentication Protocol (EAP) exchange reserved solely for the purpose of deriving master keys for one or Salowey, et al. Expires July 15, 2007 [Page 1] Internet-Draft USRK Derivation January 2007 more purposes identified as usage definitions. This document specifies a mechanism for deriving cryptographically separate root keys from the EMSK, called usage specific root Keys (USRK). The document provides a set of requirements for avoiding conflicts between usage definitions to ensure this cryptographic separation. The USRK is used according to the usage definition defined for a specific purpose. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Cryptographic Separation and Coordinated Key Derivation . . . 4 3. USRK Key Derivation Framework . . . . . . . . . . . . . . . . 5 3.1 The USRK Key Derivation Function . . . . . . . . . . . . 6 3.2 Default PRF . . . . . . . . . . . . . . . . . . . . . . . 7 3.3 Key Naming and Usage Data . . . . . . . . . . . . . . . . 7 4. Requirements for Usage Definitions . . . . . . . . . . . . . . 8 4.1 USRK Management Guidelines . . . . . . . . . . . . . . . . 8 5. Requirements for EAP System . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6.1 Key strength . . . . . . . . . . . . . . . . . . . . . . . 10 6.2 Cryptographic separation of keys . . . . . . . . . . . . . 10 6.3 Implementation . . . . . . . . . . . . . . . . . . . . . . 10 6.4 Key Distribution . . . . . . . . . . . . . . . . . . . . . 10 6.5 Key Lifetime . . . . . . . . . . . . . . . . . . . . . . . 11 6.6 Entropy consideration . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7.1 USRK Key Labels . . . . . . . . . . . . . . . . . . . . . 11 7.2 PRF numbers . . . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1 Normative References . . . . . . . . . . . . . . . . . . . 13 9.2 Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . 15 Salowey, et al. Expires July 15, 2007 [Page 2] Internet-Draft USRK Derivation January 2007 1. Introduction This document deals with keys generated by authenticated key exchange mechanisms defined within the EAP framework [RFC3748]. EAP defines two types of keying material; a Master Session Key (MSK) and an Extended Master Session Key (EMSK). The EAP specification implicitly assumes that the MSK produced by EAP will be used for a single purpose at a single device, however it does reserve the EMSK for future use. This document defines the EMSK to be used solely for deriving root keys using the key derivation specified. The root keys are called usage specific root keys (USRK). This document also provides guidelines for creating usage definitions for the various uses of EAP key material and for the management of the USRKs. Note that previously USRKs were referred to as application master session keys (AMSKs); however this term proved to be confusing as it suggests a particular class of usages dealing with higher layer applications that it was not limited to serve. In this document, the terms application and usage (or "usage definition") refer to a specific use case of the EAP keying material for which a USRK is derived. Different uses for keys derived from the EMSK have been proposed. Some examples include hand off across access points in various mobile technologies, mobile IP authentication and higher layer application authentication. In order for a particular usage of EAP key material to make use of this specification it must specify a usage definition. This document does not define how the derived USRKs should be used or discuss what types of use cases are valid. It does define a framework for the derivation of USRKs for different purposes such that different usages can be developed independently from one another. The goal is to have security properties of one usage have minimal affect on the security properties of other usages. In order to keep specific uses separate from one another two requirements are defined in the following sections. One is coordinated key derivation and another is cryptographic separation. 1.1 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] The following terms are taken from [RFC3748]: EAP Server, peer, authenticator, Master Session Key (MSK), Extended Master Session Key Salowey, et al. Expires July 15, 2007 [Page 3] Internet-Draft USRK Derivation January 2007 (EMSK), Cryptographic Separation. Usage Definition An application of cryptographic key material to provide one or more security functions such as authentication, authorization, encryption or integrity protection for related applications or services. This document provides guidelines and recommendations for what should be included in usage definitions. This document does not place any constrains on the types of use cases or services that create usage definitions. Usage Specific Root Key (USRK) Keying material derived from the EMSK for a particular usage definition as specified in this document. It is used to derive child keys in a way defined by its usage definition. 2. Cryptographic Separation and Coordinated Key Derivation The EMSK is used to derive keys for multiple use cases, and thus it is required that the derived keys are cryptographically separate. Cryptographic separation means that when multiple keys are derived from an EMSK, given any derived key it is computationally infeasible to derive any of the other derived keys. Note that deriving the EMSK from any combinations of the derived keys must also be computationally infeasible. In practice this means that derivation of an EMSK from a derived key or derivation of one child key from another must require an amount of computation equivalent to that required to, say, reversing a cryptographic hash function. Cryptographic separation of keys derived from the same key can be achieved in many ways. Two obvious methods are as follows: it is plausible to use the IKEv2 PRF [RFC4306] on the EMSK and generate a key stream. Keys of various lengths as required may be provided from the key stream for various uses. The other option is to derive keys from EMSK by providing different inputs to the PRF. However, it is desirable that derivation of one child key from the EMSK is independent of derivation of another child key. This allows child keys to be derived in any order, independent of other keys. Thus it is desirable to use the second option from above. That implies the additional input to the PRF must be different for each child key derivation. This additional input to the PRF must be coordinated properly to meet the requirement of cryptographic separation and to prevent reuse of key material between usages. If cryptographic separation is not maintained then the security of Salowey, et al. Expires July 15, 2007 [Page 4] Internet-Draft USRK Derivation January 2007 one usage depends upon the security of all other usages that use key derived from the EMSK. If a system does not have this property then a usage's security depends upon all other usages deriving keys from the same EMSK, which is undesirable. In order to prevent security problems in one usage from interfering with another usage, the following cryptographic separation is required: o It MUST be computationally infeasible to compute the EMSK from any USRK. o Any USRK must be cryptographically separate from any other USRK derived from the same EMSK o Derivation of USRKs must be coordinated so that two separate cryptographic usages do not derive the same key. This document provides guidelines for a mechanism, which can be used with existing and new EAP methods to provide cryptographic separation between usages of EAP keying material. This allows for the development of new usages without cumbersome coordination between different usage definitions. 3. USRK Key Derivation Framework The USRK key derivation framework provides a coordinated means for generating multiple USRKs from an EMSK. Further keys may then be derived from the USRK for various purposes, including encryption, integrity protection, entity authentication by way of proof of possession, and subsequent key derivation. The usages of the USRK are set forth in a usage definition described in Section 4. The USRK key derivation function (KDF) derives an USRK from the EMSK described above, a key label, optional data, and output length. The KDF is expected to give the same output for the same input. The basic key derivation function is given below. USRK = KDF(EMSK, key label, optional data, length) The key labels are printable ASCII strings unique for each usage definition and are a maximum of 255 bytes. In general they are of the form label-string@domain where domain is the organization that controls the specification of the usage definition of the USRK. The key label is intended to provide global uniqueness. Rules for the allocation of these labels are given in Section 7. For the optional data the KDF MUST be capable of processing at least 2048 opaque octets. The optional data must be constant during the execution of the KDF. The length is a 2 byte unsigned integer in network byte order of the output key length in octets. An implementation of the KDF MUST be capable of producing at least 2048 octets of output, however it is RECOMMENDED that USRKs be 64 octets long. Salowey, et al. Expires July 15, 2007 [Page 5] Internet-Draft USRK Derivation January 2007 A usage definition requiring derivation of an USRK must specify all the inputs (other than EMSK) to the key derivation function. 3.1 The USRK Key Derivation Function The EMSK key derivation function is based on a pseudo random function (PRF) that has the following function prototype: KDF = PRF(key, data) where: key = EMSK data = label + "\0" + op-data + length label = ASCII key label op-data = optional data length = 2 byte unsigned integer in network byte order '\0' = is a NUL byte (0x00 in hex) + denotes concatenation The NUL byte after the key label is used to avoid collisions if one key label is a prefix of another label (e.g. "foobar" and "foobarExtendedV2"). This is considered a simpler solution than requiring a key label assignment policy that prevents prefixes from occurring. This specification allows for the use of different PRFs. However, in order to have a coordinated key derivation function the same PRF function MUST be used for all key derivations for a given EMSK. If no PRF is specified, then the default PRF specified in Section 3.2 MUST be used. A system may provide the capability to negotiate additional PRFs. PRFs are assigned numbers through IANA following the policy set in section Section 7. The rules for negotiating a PRF are as follows: o If no other PRF is specified the PRF specified in this document MUST be used. This is the "default" PRF. o The initial authenticated key exchange MAY specify a favored PRF. For example an EAP method may define a preferred PRF to use in its specification. If the initial authenticated key exchange specifies a PRF then this MUST override the default PRF. o If the authenticated EAP key exchange is carried within another lower layer protocol that has negotiation capabilities then this protocol MAY attempt to negotiate a PRF to use. < editor's note: Is this a good idea, the concern is that it may lead to usage definitions trying to control what the PRF which may be difficult Salowey, et al. Expires July 15, 2007 [Page 6] Internet-Draft USRK Derivation January 2007 to manage. > o If the system allows a lower layer protocol to negotiates a PRF then the negotiated PRF MUST be used. It SHOULD take into account any hints that are provide by the authenticated key exchange. Note that this capability MUST protect against bidding down attacks. o A system MAY specify a separate default PRF if all participants within the system have the knowledge of which PRF to use. If specified this MUST take precedence over key exchange defined PRF. Note that usage definitions MUST not concern themselves with the details of the PRF construction or the PRF selection, they only need to worry about the inputs specified in Section 3. 3.2 Default PRF The default PRF for deriving USRKs from an EMSK is taken from the PRF+ key expansion PRF from [RFC4306] based on HMAC-SHA-256 [SHA256]. The prf+ construction was chosen because of its simplicity and efficiency over other PRFs such as those used in [RFC2246]. The motivation for the design of this PRF is described in [SIGMA]. The definition of PRF+ from [RFC4306]is given below: prf+ (K,S) = T1 | T2 | T3 | T4 | ... Where: T1 = prf (K, S | 0x01) T2 = prf (K, T1 | S | 0x02) T3 = prf (K, T2 | S | 0x03) T4 = prf (K, T3 | S | 0x04) continuing as needed to compute the required length of key material. The key, K, is the EMSK and S is the data defined in Section 3.1. For this specification the PRF is taken as HMAC-SHA-256 [SHA256]. Since PRF+ is only defined for 255 iterations it may produce up to 8160 bytes of key material. 3.3 Key Naming and Usage Data It is RECOMMENDED that the authenticated key exchange export a value, an EAP Session-ID, that is known to both sides to provide a way to identify the exchange and the keys derived by the exchange. The EAP keying framework [I-D.ietf-eap-keying] defines this value and provides an example of how to name an EMSK. The use of names based on the Session-ID in [I-D.ietf-eap-keying] is RECOMMENDED. Salowey, et al. Expires July 15, 2007 [Page 7] Internet-Draft USRK Derivation January 2007 It is RECOMMENDED that each root key has a name derived as follows: USRK key name = prf-64( EAP Session-ID, key-label ) where prf-64 is the first 64 bits from the output Usage definitions MAY use the EAP session-ID in the specification of the optional data parameter that go into the KDF function. This provides the advantage of providing data into the key derivation that is unique to the session that generated the keys. 4. Requirements for Usage Definitions In order for a usage definition to meet the guidelines for USRK usage it must meet the following recommendations: o The usage definition MUST NOT use the EMSK in any other way except to derive USRKs using the key derivation specified in Section 3 of this document. They MUST NOT use the EMSK directly. o The usage definition SHOULD NOT require caching of the EMSK. It is RECOMMENDED that the USRK derived specifically for the usage definition rather than the EMSK should be used as a root key to derive child keys for specific cryptographic operations. o Usage definition MUST define distinct key labels and optional data used in the key derivation described in Section 3. Usage definitions are encouraged to use the key name described in Section 3.3 and include additional data in the optional data to provide additional entropy. o Usage definitions MUST define the length of their USRK. It is RECOMMENDED that the USRK be at least as long as the EMSK (64 bytes). o Usage definitions MUST define how they use their USRK. This includes aspects of key management covered in the next section on USRK Management guidelines. 4.1 USRK Management Guidelines This section makes recommendations for various aspects of key management of the USRK including lifetime, child key derivation, caching and transport. It is RECOMMENDED that the USRK only used as a root key for deriving child keys. A usage definition must specify how and when the derivation of child keys should be done. It is RECOMMENDED that usages following similar considerations for key derivation are as outlined in this document for the USRK derivation with respect to cryptographic separation and key reuse. In addition, usages should take into consideration the number of keys that will be derived from Salowey, et al. Expires July 15, 2007 [Page 8] Internet-Draft USRK Derivation January 2007 the USRK and ensure that enough entropy is introduced in the derivation to support this usage. It is desirable that the entropy is provided by the two parties that derive the child key. USRKs have the same lifetime as the EMSK. Thus, when the EMSK expires, the USRKs derived from it should be removed from use. If a new EMSK is derived from a subsequent EAP transaction then a usage implementation should begin to use the new USRK derived from the new EMSK as soon as possible. Whether or not child keys associated with a USRK are replaced depends on the requirements of the usage definition. It is conceivable that some usage definition forces the child key to be replaced and others allow child keys to be used based on the policy of the entities that use the child key. Recall that the EMSK never leaves the EAP peer and server. That also holds true for some USRKs; however, some USRKs may be provided to other entities for child key derivation and delivery. Each usage definition specification will specify delivery caching and/or delivery procedures. Note that the purpose of the key derivation in Section 3 is to ensure that USRKs are cryptographically separate from each other and the EMSK. In other words, given an USRK, it is computationally infeasible to derive the EMSK, any other USRKs, or child keys associated with other USRKs. In addition to the USRK, several other parameters may need to be sent. USRK name should be derived from the EMSK key name, and thus the key name needs to be sent along with the key. When USRKs are delivered to another entity, the lifetime associated with the specific root keys MUST also be transported to that entity. Recommendations for transporting keys are discussed in the security considerations (Section 6.4). Usage definition may also define how keys are bound to particular usages entities. This can be done through the inclusion of usage parameters and identities in the child key derivation. Some of this data is described as "channel bindings" in [RFC3748]. 5. Requirements for EAP System The system that wishes to make use of EAP USRKs must take certain things into consideration. The following is a list of these considerations: o The EMSK MUST NOT be used for any other purpose than the key derivation described in this document. Salowey, et al. Expires July 15, 2007 [Page 9] Internet-Draft USRK Derivation January 2007 o The EMSK MUST be secret and not known to someone observing the authentication mechanism protocol exchange. o The EMSK MUST be maintained within a protected location inside the entity where it is generated. Only keys (USRKs) derived according to this specification may be exported from this boundary. o The EMSK MUST be unique for each session o The EAP method MUST provide an identifier for the EAP transaction that generated the key o The system MUST define which usage definitions are used and how they are invoked. o The system may define ways to select an alternate PRF for key derivation as defined in Section 3.1. The system MAY use the MSK transmitted to the NAS in any way it chooses. This is required for backward compatibility. New usage definitions following this specification MUST NOT use the MSK. If more than one usage uses the MSK, then the cryptographic separation is not achieved. Implementations MUST prevent such combinations. 6. Security Considerations 6.1 Key strength The effective key strength of the derived keys will never be greater than the strength of the EMSK (or a master key internal to an EAP mechanism). 6.2 Cryptographic separation of keys The intent of the KDF is to derive keys that are cryptographically separate: the compromise of one of the usage specific root keys (USRKs) should not compromise the security of other USRKs or the EMSK. It is believed that the KDF chosen provides the desired separation. 6.3 Implementation An implementation of an EAP framework should keep the EMSK internally as close to where it is derived as possible and only provide an interface for obtaining USRKs. It may also choose to restrict which callers have access to which keys. A usage definition MUST NOT assume that any entity outside the EAP server or EAP peer EAP framework has access to the EMSK. In particular it MUST NOT assume that a lower layer has access to the EMSK. 6.4 Key Distribution In some cases it will be necessary or convenient to distribute USRKs Salowey, et al. Expires July 15, 2007 [Page 10] Internet-Draft USRK Derivation January 2007 from where they are generated. Since these are secret keys they MUST be transported with their integrity and confidentiality maintained. They MUST be transmitted between authenticated and authorized parties. It is also important that the context of the key usage be transmitted along with the key. This includes information to identify the key and constraints on its usage such as lifetime. This document does not define a mechanism for key transport. It is up to usage definitions and the systems that use them to define how keys are distributed. Usage definition designers may enforce constraints on key usage by various parties by deriving a key hierarchy and by providing entities only with the keys in the hierarchy that they need. 6.5 Key Lifetime The key lifetime is dependent upon how the key is generated and how the key is used. Since the USRK is the responsibility of the usage definition it must determine how long the key is valid for. If key lifetime or key strength information is available from the authenticated key exchange then this information SHOULD be used in determining the lifetime of the key. If possible it is recommended that key lifetimes be coordinated throughout the system. Setting a key lifetime shorter that a system lifetime may result is keys becoming invalid with no convenient way to refresh them. Setting a key lifetime to longer may result in decreased security since the key may be used beyond its recommended lifetime. 6.6 Entropy consideration The number of root keys derived from the EMSK is expected to be low. Note that there is no randomness required to be introduced into the EMSK to root key derivation beyond the root key labels. Thus, if many keys are going to be derived from an USRK it is important that USRK to child key derivation introduce fresh random numbers in deriving each key. 7. IANA Considerations The keywords "PRIVATE USE", "SPECIFICATION REQUIRED" and "IETF CONSENSUS" that appear in this document when used to describe namespace allocation are to be interpreted as described in [RFC2434]. 7.1 USRK Key Labels This specification introduces a new name space for "USRK key labels". Key labels are of one of two formats: "label-string" or "label-string@domain" (without the double quotes). Salowey, et al. Expires July 15, 2007 [Page 11] Internet-Draft USRK Derivation January 2007 Labels of the form "label-string" registered by the IANA MUST be printable US-ASCII strings, and MUST NOT contain the characters at- sign ("@"), comma (","), whitespace, control characters (ASCII codes 32 or less), or the ASCII code 127 (DEL). Labels are case-sensitive, and MUST NOT be longer than 64 characters. Labels of this form are assigned based on the IETF CONSENSUS policy. Labels with the at-sign in them of the form "label-string@domain" where the part preceding the at-sign is the label. The format of the part preceding the at-sign is not specified; however, these labels MUST be printable US-ASCII strings, and MUST NOT contain the comma character (","), whitespace, control characters (ASCII codes 32 or less), or the ASCII code 127 (DEL). They MUST have only a single at- sign in them. The part following the at-sign MUST be a valid, fully qualified internet domain name [RFC1034] controlled by the person or organization defining the label. Labels are case-sensitive, and MUST NOT be longer than 64 characters. It is up to each domain how it manages its local namespace. Note that the total number of octets in a label is limited to 255. It has been noted that these labels resemble STD 11 [RFC0822] addresses and network access identifiers (NAI) defined in [RFC4282]. This is purely coincidental and has nothing to do with STD 11 [RFC0822] or [RFC4282]. An example of a locally defined label is "service@example.com" (without the double quotes). Labels within the "ietf.org" domain are assigned based on the IETF CONSENSUS policy with specification recommended. Labels from other domains may be registered with IANA by the person or organization controlling the domain with an assignment policy of SPECIFICATION REQUIRED. It is RECOMMENDED that the specification contain the following information: o A description of the usage o The key label to be used o Length of the USRK o If optional data is used, what it is and how it is maintained o How child keys will be derived from the USRK and how they will be used o How lifetime of the USRK and its child keys will be managed o Where the USRKs or child keys will be used and how they are communicated if necessary 7.2 PRF numbers This specification introduces a new number space for "EMSK PRF numbers". The numbers are int he range 0 to 255 Numbers from 0 to 220 are assigned through the policy IETF CONSENSUS and numbers in the Salowey, et al. Expires July 15, 2007 [Page 12] Internet-Draft USRK Derivation January 2007 range 221 to 255 are left for PRIVATE USE. The initial registry should contain the following values: 0 RESERVED 1 HMAC-SHA-256 PRF+ (Default) 8. Acknowledgements This document expands upon previous collaboration with Pasi Eronen. This document reflects conversations with Bernard Aboba, Jari Arkko, Avi Lior, David McGrew, Henry Haverinen, Hao Zhou and members of the EAP working group. 9. References 9.1 Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [SHA256] National Institute of Standards and Technology, "Secure Hash Standard", FIPS 180-2, August 2002. With Change Notice 1 dated February 2004 9.2 Informative References [I-D.ietf-eap-keying] Aboba, B., "Extensible Authentication Protocol (EAP) Key Management Framework", draft-ietf-eap-keying-16 (work in progress), January 2007. [RFC0822] Crocker, D., "Standard for the format of ARPA Internet text messages", STD 11, RFC 822, August 1982. [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", Salowey, et al. Expires July 15, 2007 [Page 13] Internet-Draft USRK Derivation January 2007 STD 13, RFC 1034, November 1987. [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network Access Identifier", RFC 4282, December 2005. [SIGMA] Krawczyk, H., "SIGMA: the 'SIGn-and-MAc' Approach to Authenticated Diffie-Hellman and its Use in the IKE Protocols", LNCS 2729, Springer, 2003. Available at http://www.informatik.uni-trier.de/~ley/db/ conf/crypto/crypto2003.html Authors' Addresses Joseph Salowey Cisco Systems Email: jsalowey@cisco.com Lakshminath Dondeti Qualcomm, Inc Email: ldondeti@qualcomm.com Vidya Narayanan Qualcomm, Inc Email: vidyan@qualcomm.com Madjid Nakhjiri Huawei USA Email: mnakhjiri@huawei.com Salowey, et al. Expires July 15, 2007 [Page 14] Internet-Draft USRK Derivation January 2007 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Salowey, et al. Expires July 15, 2007 [Page 15]