Secure Shell Working Group J. Galbraith Internet-Draft VanDyke Software Expires:
September 23,October 21, 2005 O. Saarenmaa F-Secure March 22,Corporation April 19, 2005 X.509 authentication in SSH2 draft-ietf-secsh-x509-00.txtdraft-ietf-secsh-x509-01.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667.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 becomebecomes aware will be disclosed, in accordance with RFC 3668.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. 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 September 23,October 21, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The X.509 extension specifies how X.509 keys and signatures are used within the SSH2 protocol. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. x509v3 keysCertificate validation . . . . . . . . . . . . . . . . . . . . 3 2.1 Host Authentication . . . . . 4 2.1 x509v3-sign-rsa2. . . . . . . . . . . . . . 3 2.2 User Authentication . . . . . . . . 4 2.2 x509v3-sign-dss2. . . . . . . . . . . 3 3. Use in SSH2 Protocol . . . . . . . . . . . . . . . . . . . . . 3 3.1 x509v3-sign-rsa-sha1 . . . . . . . . . . . . . . . . . . . 4 2.33.2 x509v3-sign-dss-sha1 . . . . . . . . . . . . . . . . . . . 4 3.3 x509v3-sign . . . . . . . . . . . . . . . . . . . . . . . 5 3.4 4. Implementation Considerations . . . . . . . . . . . . . . . . 6 4.5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5.5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6.5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6.16 7.1 Normative References . . . . . . . . . . . . . . . . . . . 9 6.26 7.2 Informative References . . . . . . . . . . . . . . . . . . 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 107 Intellectual Property and Copyright Statements . . . . . . . . 118 1. Introduction The SSH protocol can use public keys for both host and user authentication. However, particularly for host authentication, plain public keys lack a good method of verifying that the the key provided really does belong to the host asserting ownership. X.509v3 certificates can address this problem in environments where a PKI infrastructure is available. 2. x509v3 keysCertificate validation Implementations are expected to follow the basic certificate and certificate path validation guidelines described in [RFC3280]. No SSH specific X.509 certificate extensions are defined in this document. 2.1 Host Authentication The client MAY verify that the serverAuth option, as specified in [RFC3280], is present in the host certificate's extendedKeyUsage field. Implementations SHOULD validate the host certificates by matching the host's fully qualified domain name [RFC1034] against the host certificate's subjectAltName extensions's dNSName entries. If the certificate does not contain dNSName subjectAltName extensions, the (most specific) Common Name field in the certificate Subject is to be used. This is similiar to host validation in [RFC2818]. 2.2 User Authentication The server MAY verify that the clientAuth option, as specified in [RFC3280], is present in the user certificate's extendedKeyUsage field. No constraints are placed on the presence of user accounts in the certificates used for user authentication. Their validation is left as an implementation and configuration detail for the implementors and deployers. 3. Use in SSH2 Protocol Key type names are of the form "x509v3-sign*". Keys are encoded as follows: string key-type-name string DER encoded x.509v3 certificate data 2.1 x509v3-sign-rsa23.1 x509v3-sign-rsa-sha1 Certificates that use the RSA public key algorithm SHOULD use the "x509v3-sign-rsa2""x509v3-sign-rsa-sha1" key-type-name. Signing and verifying using this key format, uses the certificate's private key, in exactly the same manner specified for "ssh-rsa" public keys in [I-D.ietf-secsh-transport]. That is to say, signing and verifying using this key format is performed according to the RSASSA-PKCS1-v1_5 scheme in [RFC3447] using the SHA-1 hash. The signature format for x509v3-sign-rsa2x509v3-sign-rsa-sha1 certificates is the "ssh-rsa" signing format specified in [I-D.ietf-secsh-transport]. This format is as follows: string "ssh-rsa" string rsa_signature_blob The value for 'rsa_signature_blob' is encoded as a string containing s (which is an integer, without lengths or padding, unsigned and in network byte order). 2.2 x509v3-sign-dss23.2 x509v3-sign-dss-sha1 Certificates that use the DSA public key algorithm SHOULD use the "x509v3-sign-dss2""x509v3-sign-dss-sha1" key-type-name. Signing and verifying using this key format, uses the certificate's private key, in exactly the same manner specified for "ssh-dss" public keys in [I-D.ietf-secsh-transport]. That is to say, signing and verifying using this key format is done according to the Digital Signature Standard [FIPS-186-2] using the SHA-1 hash [FIPS-180-2]. The signature format for x509v3-sign-rsa2x509v3-sign-dss-sha1 certificates is the "ssh-dss" signing format specified in [I-D.ietf-secsh-transport]. This format is as follows: string "ssh-dss" string dss_signature_blob The value for 'dss_signature_blob' is encoded as a string containing r followed by s (which are 160-bit integers, without lengths or padding, unsigned and in network byte order). 2.33.3 x509v3-sign Certificates that use another algorithm other than the two specified above, MUST use the "x509v3-sign" key-type-name. Signing and verifying is done according to the specification associated with the public-key algorithm oid encoded in the certificate. The signature, and description of the signature algorithms is encoded as specificied in pkcs7[PKCS.7.1993]. The signature MUST be detached (the signed data MUST NOT be includeded in the pkcs7 data.data). The pkcs7 data is encoded in the SSH protocol as follows: string "pkcs7" string DER encoded PKCS7 data 3.4. Implementation Considerations Implemenations SHOULDshould be careful when using x.509v3 certificates as hostkeys. If the peer does not implement the required algorithms to validate both the x.509v3 certificate and all certificates in the chain, it MUST disconnect. There is no way to renegotiate the key during key exchange. This is especially true when using the "x509v3-sign" key type, since in this case the peer has no knowledge whatsoever of required algorithms. 4.5. IANA Considerations This document reserves all key types beginning with "x509v3-sign" in the SSH publickey type registery. This document specifically adds "x509v3-sign-rsa2", "x509v3-sign-dss2","x509v3-sign-rsa-sha1", "x509v3-sign- dss-sha1", and "x509v3-sign" to the SSH publickey type registry. This document adds "x509v3-sign-rsa" and "x509v3-sign-dss" to the SSH publickey type registry as "poisoned" by historical use. 5.6. Security Considerations PKI is an extremely complex topic, and care MUSTmust be taken by both implementors and deployers to understand the complex interactions involved. Implementations SHOULDshould carefully validate the certificate, including, but not limitted to, certificate expiration, certificate signature, certificate revokation lists, etc. For more information, implementors should refer to [ITU.X509.2000] and [RFC3820]. 6.[RFC3280]. 7. References 6.17.1 Normative References [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002. [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, February 2003. [I-D.ietf-secsh-transport] Lonvick, C., "SSH Transport Layer Protocol", Internet-Draft draft-ietf-secsh-transport-24,draft-ietf-secsh-transport-24 (work in progress), March 2005. [PKCS.7.1993] RSA Laboratories, "Cryptographic Message Syntax Standard. Version 1.5", PKCS 7, November 1993. [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, February 2003. [RFC3820] Tuecke, S., Welch, V., Engert, D., Pearlman, L. and M. Thompson, "Internet X.509 Public Key Infrastructure (PKI) Proxy Certificate Profile", RFC 3820, June 2004. [ITU.X509.2000] International Telecommunications Union, "Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks", ITU-T Recommendation X.509, ISO Standard 9594-8, March 2000.[FIPS-180-2] National Institute of Standards and Technology, "Secure Hash Standard (SHS)", Federal Information Processing Standards Publication 180-2, August 2002. [FIPS-186-2] National Institute of Standards and Technology, "Digital Signature Standard (DSS)", Federal Information Processing Standards Publication 186-2, January 2000. 6.2[ITU.X509.2000] International Telecommunications Union, "Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks", ITU- T Recommendation X.509, ISO Standard 9594-8, March 2000. 7.2 Informative References [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. Authors' Addresses Joseph Galbraith VanDyke Software 4848 Tramway Ridge Blvd Suite 101 Albuquerque, NM 87111 US Phone: +1 505 332 5700 Email: firstname.lastname@example.org Oskari Saarenmaa F-Secure A Street Address A City, State or Region A Postal CodeCorporation Tammasaarenkatu 7 Helsinki 00180 FI Email: email@example.com Trademark notice "ssh" is a registered trademark in the United States and/or other countries. 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. 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