S/MIME Working Group R. Housley Internet Draft RSA Laboratories expires in six months July 2002 Use of the RSAES-OAEP Key Transport Algorithm in CMS Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes the use of the RSAES-OAEP key transport method of key management within the Cryptographic Message Syntax (CMS). 1. Introduction This draft is being discussed on the "ietf-smime" mailing list. To join the list, send a message to with the single word "subscribe" in the body of the message. Also, there is a Web site for the mailing list at . PKCS #1 Version 1.5 [PKCS#1v1.5] specifies a widely deployed variant of the RSA key transport algorithm. PKCS #1 Version 1.5 key Housley [Page 1] INTERNET DRAFT July 2002 transport is vulnerable to adaptive chosen ciphertext attacks, especially when it is used to for key management in interactive applications. This attack is often referred to as the "Million Message Attack," and it explained in [RSALABS] and [CRYPTO98]. Exploitation of this vulnerability, which reveals the result of a particular RSA decryption, requires access to an oracle which will respond to hundreds of thousands of ciphertexts, which are constructed adaptively in response to previously received replies that provide information on the successes or failures of attempted decryption operations. The attack is significantly less feasible in store-and-forward environments, such as S/MIME. RFC 3218 [MMA] discussed the countermeasures to this attack that are available when PKCS #1 Version 1.5 key transport is used in conjunction with the Cryptographic Message Syntax (CMS) [CMS]. When PKCS #1 Version 1.5 key transport is applied as an intermediate encryption layer within an interactive request-response communications environment, exploitation could be more feasible. However, Secure Sockets Layer (SSL) [SSL] and Transport Layer Security (TLS) [TLS] protocol implementations could include countermeasures that detect and prevent the Million Message Attack and other chosen-ciphertext attacks. These countermeasures are performed within the protocol level. In the interest of long-term security assurance, it is prudent to adopt an improved cryptographic technique rather than embedding countermeasures within protocols. To this end, an updated version of PKCS #1 has been published. PKCS #1 Version 2.0 [PKCS#1v2.0] supersedes RFC 2313. It preserves support for the PKCS #1 Version 1.5 encryption padding format, and it also defines a new one. To resolve the adaptive chosen ciphertext vulnerability, the PKCS #1 Version 2.0 specifies and recommends use of Optimal Asymmetric Encryption Padding (OAEP) for RSA key transport. This document specifies the use of RSAES-OAEP key transport algorithm in the CMS. The CMS can be used in either a store-and-forward or an interactive request-response environment. The CMS supports variety of architectures for certificate-based key management, particularly the one defined by the PKIX working group [PROFILE]. PKCS #1 Version 1.5 and PKCS #1 Version 2.0 require the same RSA public key information. Thus, a certified RSA public key may be used with either RSA key transport technique. The CMS uses ASN.1 [X.208-88], the Basic Encoding Rules (BER) [X.209-88], and the Distinguished Encoding Rules (DER) [X.509-88]. Housley [Page 2] INTERNET DRAFT July 2002 Throughout this document, when the terms "MUST," "MUST NOT," "SHOULD," and "MAY" are used in capital letters, their use conforms to the definitions in RFC 2119 [STDWORDS]. These key word definitions help make the intent of standards documents as clear as possible. These key words are used in this document to help implementers achieve interoperability. 2. Enveloped-data Conventions The CMS enveloped-data content type consists of an encrypted content and wrapped content-encryption keys for one or more recipients. The RSAES-OAEP key transport algorithm is used to wrap the content- encryption key for one recipient. Compliant software MUST meet the requirements for constructing an enveloped-data content type stated in [CMS] Section 6, "Enveloped- data Content Type". A content-encryption key MUST be randomly generated for each instance of an enveloped-data content type. The content-encryption key is used to encipher the content. 2.1. EnvelopedData Fields The enveloped-data content type is ASN.1 encoded using the EnvelopedData syntax. The fields of the EnvelopedData syntax MUST be populated as described in this section when RSAES-OAEP key transport is employed for one or more recipients. The EnvelopedData version MUST be 0, 2, or 3. The EnvelopedData originatorInfo field is not used for the RSAES-OAEP key transport algorithm. However, this field MAY be present to support recipients using other key management algorithms. The EnvelopedData recipientInfos CHOICE MUST be KeyTransRecipientInfo. See section 2.2 for further discussion of KeyTransRecipientInfo. The EnvelopedData encryptedContentInfo contentEncryptionAlgorithm field MUST be a symmetric encryption algorithm identifier. The EnvelopedData unprotectedAttrs MAY be present. 2.2. KeyTransRecipientInfo Fields The fields of the KeyTransRecipientInfo syntax MUST be populated as described in this section when RSAES-OAEP key transport is employed Housley [Page 3] INTERNET DRAFT July 2002 for one or more recipients. The KeyTransRecipientInfo version MUST be 0 or 2. If the RecipientIdentifier uses the issuerAndSerialNumber alternative, then the version MUST be 0. If the RecipientIdentifier uses the subjectKeyIdentifier alternative, then the version MUST be 2. The KeyTransRecipientInfo RecipientIdentifier provides two alternatives for specifying the recipient's certificate, and thereby the recipient's public key. The recipient's certificate MUST contain a RSA public key. The content-encryption key is encrypted with the recipient's RSA public key. The issuerAndSerialNumber alternative identifies the recipient's certificate by the issuer's distinguished name and the certificate serial number; the subjectKeyIdentifier identifies the recipient's certificate by the X.509 subjectKeyIdentifier extension value. The KeyTransRecipientInfo keyEncryptionAlgorithm specifies use of the RSAES-OAEP algorithm, and its associated parameters, to encrypt the content-encryption key for the recipient. The key-encryption process is described in [PKCS#1v2.0]. See section 3 of this document for the algorithm identifier and the parameter syntax. The KeyTransRecipientInfo encryptedKey is the result of encrypting the content-encryption key in the recipient's RSA public key using the RSAES-OAEP algorithm. The RSA public key MUST be at least 1024 bits in length. When using a Triple-DES [3DES] content-encryption key, implementations MUST adjust the parity bits to ensure odd parity for each octet of each DES key comprising the Triple-DES key prior to RSAES-OAEP encryption. 3. RSAES-OAEP Algorithm Identifiers and Parameters The RSAES-OAEP key transport algorithm is the RSA encryption scheme defined in RFC 2437 [PKCS#1v2.0], where the message to be encrypted is the content-encryption key. The algorithm identifier for RSAES- OAEP is: id-RSAES-OAEP OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 7 } The AlgorithmIdentifier parameters field MUST be present, and the parameters field MUST contain RSAES-OAEP-params. RSAES-OAEP-params has the following syntax: Housley [Page 4] INTERNET DRAFT July 2002 RSAES-OAEP-params ::= SEQUENCE { hashFunc [0] AlgorithmIdentifier DEFAULT sha1Identifier, maskGenFunc [1] AlgorithmIdentifier DEFAULT mgf1SHA1Identifier, pSourceFunc [2] AlgorithmIdentifier DEFAULT pSpecifiedEmptyIdentifier } sha1Identifier AlgorithmIdentifier ::= { id-sha1, NULL } mgf1SHA1Identifier AlgorithmIdentifier ::= { id-mgf1, sha1Identifier } pSpecifiedEmptyIdentifier AlgorithmIdentifier ::= { id-pSpecified, nullOctetString } nullOctetString OCTET STRING (SIZE (0)) ::= { ''H } id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) oiw(14) secsig(3) algorithms(2) 26 } pkcs-1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) } id-mgf1 OBJECT IDENTIFIER ::= { pkcs-1 8 } id-pSpecified OBJECT IDENTIFIER ::= { pkcs-1 9 } The fields within RSAES-OAEP-params have the following meanings: hashFunc identifies the one-way hash function. Implementations MUST support SHA-1 [SHA1], and implementations MAY support other one-way hash functions. The SHA-1 algorithm identifier is comprised of the id-sha1 object identifier and a parameter of NULL. Implementations that perform encryption MUST omit the hashFunc field when SHA-1 is used, indicating that the default algorithm was used. Implementations that perform decryption MUST recognize both the id-sha1 object identifier and an absent hashFunc field as an indication that SHA-1 was used. maskGenFunc identifies the mask generation function. Implementations MUST support MFG1 [PKCS#1v2.0]. MFG1 requires a one-way hash function, and it is identified in the parameter field of the MFG1 algorithm identifier. Implementations MUST support SHA-1 [SHA1], and implementations MAY support other one-way hash functions. The MFG1 algorithm identifier is comprised of the id- mgf1 object identifier and a parameter that contains the algorithm identifier of the one-way hash function employed with MFG1. The SHA-1 algorithm identifier is comprised of the id-sha1 object Housley [Page 5] INTERNET DRAFT July 2002 identifier and a parameter of NULL. Implementations that perform encryption MUST omit the maskGenFunc field when MFG1 with SHA-1 is used, indicating that the default algorithm was used. Implementations that perform decryption MUST recognize both the id-mgf1 and id-sha1 object identifiers as well as an absent maskGenFunc field as an indication that MFG1 with SHA-1 was used. pSourceFunc identifies the source (and possibly the value) of the encoding parameters, commonly called P. Implementations MUST represent P by an algorithm identifier, id-pSpecified, indicating that P is explicitly provided as an OCTET STRING in the parameters. The default value for P is an empty string. In this case, pHash in EME-OAEP contains the hash of a zero length string. Implementations MUST support a zero length P value. Implementations that perform encryption MUST omit the pSourceFunc field when a zero length P value is used, indicating that the default value was used. Implementations that perform decryption MUST recognize both the id-pSpecified object identifier and an absent pSourceFunc field as an indication that a zero length P value was used. 4. SMIMECapabilities Attribute Conventions RFC 2633 [MSG], Section 2.5.2 defines the SMIMECapabilities signed attribute (defined as a SEQUENCE of SMIMECapability SEQUENCEs) to be used to specify a partial list of algorithms that the software announcing the SMIMECapabilities can support. When constructing a signedData object, compliant software MAY include the SMIMECapabilities signed attribute announcing that it supports the RSAES-OAEP algorithm. When all of the default settings are selected, the SMIMECapability SEQUENCE representing RSAES-OAEP MUST include the id-RSAES-OAEP object identifier in the capabilityID field and MUST include an empty SEQUENCE in the parameters field. In this case, RSAES-OAEP is represented by the rSAES-OAEP-Default-Identifier: rSAES-OAEP-Default-Identifier AlgorithmIdentifier ::= { id-RSAES-OAEP, { sha1Identifier, mgf1SHA1Identifier, pSpecifiedEmptyIdentifier } } The SMIMECapability SEQUENCE representing rSAES-OAEP-Default- Identifier MUST be DER-encoded as the following hexadecimal string: 30 0D 06 09 2A 86 48 86 F7 0D 01 01 07 30 00 Housley [Page 6] INTERNET DRAFT July 2002 When settings other than the defaults are selected, the SMIMECapability SEQUENCE representing RSAES-OAEP MUST include the id-RSAES-OAEP object identifier in the capabilityID field and MUST include the RSAES-OAEP-params SEQUENCE that identifies the non-default settings in the parameters field. When SHA-256 is used in the hashFunc and SHA-256 is used with MGF1 in the maskGenFunc, the SMIMECapability SEQUENCE representing RSAES-OAEP is the rSAES-OAEP-SHA256-Identifier, as specified in Appendix A. The SMIMECapability SEQUENCE representing rSAES-OAEP-SHA256-Identifier MUST be DER-encoded as the following hexadecimal string: 30 38 06 09 2A 86 48 86 F7 0D 01 01 07 30 2B 30 0D 06 09 60 86 48 01 65 03 04 02 01 05 00 30 1A 06 09 2A 86 48 86 F7 0D 01 01 08 30 0D 06 09 60 86 48 01 65 03 04 02 01 05 00 When SHA-384 is used in the hashFunc and SHA-384 is used with MGF1 in the maskGenFunc, the SMIMECapability SEQUENCE representing RSAES-OAEP is the rSAES-OAEP-SHA384-Identifier, as specified in Appendix A. The SMIMECapability SEQUENCE representing rSAES-OAEP-SHA384-Identifier MUST be DER-encoded as the following hexadecimal string: 30 38 06 09 2A 86 48 86 F7 0D 01 01 07 30 2B 30 0D 06 09 60 86 48 01 65 03 04 02 02 05 00 30 1A 06 09 2A 86 48 86 F7 0D 01 01 08 30 0D 06 09 60 86 48 01 65 03 04 02 02 05 00 When SHA-512 is used in the hashFunc and SHA-512 is used with MGF1 in the maskGenFunc, the SMIMECapability SEQUENCE representing RSAES-OAEP is the rSAES-OAEP-SHA512-Identifier, as specified in Appendix A. The SMIMECapability SEQUENCE representing rSAES-OAEP-SHA512-Identifier MUST be DER-encoded as the following hexadecimal string: 30 38 06 09 2A 86 48 86 F7 0D 01 01 07 30 2B 30 0D 06 09 60 86 48 01 65 03 04 02 03 05 00 30 1A 06 09 2A 86 48 86 F7 0D 01 01 08 30 0D 06 09 60 86 48 01 65 03 04 02 03 05 00 5. References This section provides normative and informative references. 5.1. Normative References 3DES American National Standards Institute. ANSI X9.52-1998, Triple Data Encryption Algorithm Modes of Operation. 1998. Housley [Page 7] INTERNET DRAFT July 2002 CMS Housley, R. Cryptographic Message Syntax. RFC . . MSG Ramsdell, B. S/MIME Version 3 Message Specification. RFC 2633. June 1999. PKCS#1v2.0 Kaliski, B. PKCS #1: RSA Encryption, Version 2.0. RFC 2437. October 1998. PROFILE Housley, R., W. Polk, W. Ford, and D. Solo. Internet X.509 Public Key Infrastructure: Certificate and Certificate Revocation List (CRL) Profile. RFC 3280. April 2002. SHA1 National Institute of Standards and Technology. FIPS Pub 180-1: "Secure Hash Standard." April 1995. STDWORDS Bradner, S. Key Words for Use in RFCs to Indicate Requirement Levels. BCP 14, RFC 2119. March 1997. X.208-88 CCITT. Recommendation X.208: Specification of Abstract Syntax Notation One (ASN.1). 1988. X.209-88 CCITT. Recommendation X.209: Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1). 1988. X.509-88 CCITT. Recommendation X.509: The Directory - Authentication Framework. 1988. 5.2. Informative References CRYPTO98 Bleichenbacher, D. "Chosen Ciphertext Attacks Against Protocols Based on the RSA Encryption Standard PKCS #1," in H. Krawczyk (editor), Advances in Cryptology - CRYPTO '98 Proceedings, Lecture Notes in Computer Science 1462 (1998), Springer-Verlag, pp. 1-12. MMA Rescorla, E. Preventing the Million Message Attack on Cryptographic Message Syntax. RFC 3218. January 2002. NISTGUIDE National Institute of Standards and Technology. Second Draft: "Key Management Guideline, Part 1: General Guidance." June 2002. [http://csrc.nist.gov/encryption/kms/guideline-1.pdf] PKCS#1v1.5 Kaliski, B. PKCS #1: RSA Encryption, Version 1.5. RFC 2313. March 1998. Housley [Page 8] INTERNET DRAFT July 2002 RANDOM Eastlake, D., S. Crocker, and J. Schiller. Randomness Recommendations for Security. RFC 1750. December 1994. RSALABS Bleichenbacher, D., B. Kaliski, and J. Staddon. Recent Results on PKCS #1: RSA Encryption Standard. RSA Laboratories' Bulletin No. 7, June 26, 1998. [http://www.rsasecurity.com/rsalabs/bulletins] SHA2 National Institute of Standards and Technology. Draft FIPS Pub 180-2: "Specifications for the Secure Hash Standard." May 2001. [http://csrc.nist.gov/encryption/shs/dfips-180-2.pdf] SSL Freier, A., P. Karlton, and P. Kocher. The SSL Protocol, Version 3.0. Netscape Communications. November 1996. [http://wp.netscape.com/eng/ssl3/draft302.txt] TLS Dierks, T. and C. Allen. The TLS Protocol Version 1.0. RFC 2246. January 1999. 6. Security Considerations Implementations must protect the RSA private key and the content- encryption key. Compromise of the RSA private key may result in the disclosure of all messages protected with that key. Compromise of the content-encryption key may result in disclosure of the associated encrypted content. The generation of RSA public/private key pairs relies on a random numbers. The use of inadequate pseudo-random number generators (PRNGs) to generate cryptographic keys can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute force searching the whole key space. The generation of quality random numbers is difficult. RFC 1750 [RANDOM] offers important guidance in this area. Generally, good cryptographic practice employs a given RSA key pair in only one scheme. This practice avoids the risk that vulnerability in one scheme may compromise the security of the other, and may be essential to maintain provable security. While PKCS #1 Version 1.5 [PKCS#1v1.5] has been employed for both key transport and digital signature without any known bad interactions, such a combined use of an RSA key pair is not recommended in the future. Therefore, an RSA key pair used for RSAES-OAEP key transport should not also be used for other purposes. This specification requires implementation to support the SHA-1 one- Housley [Page 9] INTERNET DRAFT July 2002 way hash function for interoperability, but support for other one-way hash function is permitted. At the time of this writing, the best (known) collision attacks against SHA-1 are generic attacks with complexity 2^80, where 80 is one-half the bit length of the hash value. When a one-way hash function is used with a digital signature scheme, a collision attack is easily translated into a signature forgery. Therefore, the use of SHA-1 in a digital signature scheme provides a security level of no more than 80 bits. If a greater level of security is desired, then a secure one-way hash function with a longer hash value is needed. SHA-256, SHA-384, and SHA-512 are likely candidates [SHA2]. The metrics for choosing a one-way hash function for use in digital signatures do not directly apply to the RSAES-OAEP key transport algorithm, since a collision attack on the one-way hash function does not directly translate into an attack on the key transport algorithm, unless the encoding parameters P varies (in which case a collision the hash value for different encoding parameters might be exploited). Nevertheless, for consistency with the practice for digital signature schemes, and in case the encoding parameters P is not the empty string, it is recommended that the same rule of thumb be applied to selection of a one-way hash function for use with RSAES-OAEP. That is, the one-way hash function should be selected so that the bit length of the hash value is at least twice as long as the desired security level in bits. A 1024-bit RSA public key and SHA-1 both provide a security level of about 80 bits. In [NISTGUIDE], the National Institute of Standards and Technology suggests that a security level of 80 bits is adequate for most applications until 2015. If a security level greater than 80 bits is needed, then a longer RSA public key and a secure one-way hash function with a longer hash value are needed. Again, SHA-256, SHA-384, and SHA-512 are likely candidates for such a one-way hash function. For this reason, the algorithm identifiers for these one- way hash functions are included in the ASN.1 module in Appendix A. The same one-way hash function should be employed for the hashFunc and the maskGenFunc, but it is not required. Using the same one-way hash function reduces the potential for implementation errors. 7. Acknowledgments This document is the result of contributions from many professionals. I appreciate the hard work of all members of the IETF S/MIME Working Group. Further, I extend a special thanks to Burt Kaliski, Jakob Jonsson, Francois Rousseau, and Jim Schaad. Housley [Page 10] INTERNET DRAFT July 2002 8. Author Address Russell Housley RSA Laboratories 918 Spring Knoll Drive Herndon, VA 20170 USA rhousley@rsasecurity.com Appendix A. ASN.1 Module CMS-RSAES-OAEP { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms-rsaes-oaep(20) } DEFINITIONS IMPLICIT TAGS ::= BEGIN -- EXPORTS ALL -- IMPORTS AlgorithmIdentifier FROM PKIX1Explicit88 -- RFC 3280 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) }; pkcs-1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) } id-RSAES-OAEP OBJECT IDENTIFIER ::= { pkcs-1 7 } RSAES-OAEP-params ::= SEQUENCE { hashFunc [0] AlgorithmIdentifier DEFAULT sha1Identifier, maskGenFunc [1] AlgorithmIdentifier DEFAULT mgf1SHA1Identifier, pSourceFunc [2] AlgorithmIdentifier DEFAULT pSpecifiedEmptyIdentifier } sha1Identifier AlgorithmIdentifier ::= { id-sha1, NULL } sha256Identifier AlgorithmIdentifier ::= { id-sha256, NULL } sha384Identifier AlgorithmIdentifier ::= { id-sha384, NULL } sha512Identifier AlgorithmIdentifier ::= { id-sha512, NULL } Housley [Page 11] INTERNET DRAFT July 2002 mgf1SHA1Identifier AlgorithmIdentifier ::= { id-mgf1, sha1Identifier } mgf1SHA256Identifier AlgorithmIdentifier ::= { id-mgf1, sha256Identifier } mgf1SHA384Identifier AlgorithmIdentifier ::= { id-mgf1, sha384Identifier } mgf1SHA512Identifier AlgorithmIdentifier ::= { id-mgf1, sha512Identifier } pSpecifiedEmptyIdentifier AlgorithmIdentifier ::= { id-pSpecified, nullOctetString } nullOctetString OCTET STRING (SIZE (0)) ::= { ''H } id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) oiw(14) secsig(3) algorithms(2) 26 } id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistalgorithm(4) hashalgs(2) 1 } id-sha384 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistalgorithm(4) hashalgs(2) 2 } id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistalgorithm(4) hashalgs(2) 3 } id-mgf1 OBJECT IDENTIFIER ::= { pkcs-1 8 } id-pSpecified OBJECT IDENTIFIER ::= { pkcs-1 9 } rSAES-OAEP-Default-Identifier AlgorithmIdentifier ::= { id-RSAES-OAEP, { sha1Identifier, mgf1SHA1Identifier, pSpecifiedEmptyIdentifier } } rSAES-OAEP-SHA256-Identifier AlgorithmIdentifier ::= { id-RSAES-OAEP, { sha256Identifier, mgf1SHA256Identifier, pSpecifiedEmptyIdentifier } } Housley [Page 12] INTERNET DRAFT July 2002 rSAES-OAEP-SHA384-Identifier AlgorithmIdentifier ::= { id-RSAES-OAEP, { sha384Identifier, mgf1SHA384Identifier, pSpecifiedEmptyIdentifier } } rSAES-OAEP-SHA512-Identifier AlgorithmIdentifier ::= { id-RSAES-OAEP, { sha512Identifier, mgf1SHA512Identifier, pSpecifiedEmptyIdentifier } } END Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. In addition, the ASN.1 module presented in Appendix A may be used in whole or in part without inclusion of the copyright notice. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process shall be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Housley [Page 13]