TLS Working Group M. Badra Internet-Draft DU Intended status: Standards Track I. Hajjeh Expires: September 28, 2012 INEOVATION March 27, 2012 Credential Protection Ciphersuites for Transport Layer Security (TLS) draft-badra-tls-ciphersuite-identity-protection-00 Abstract This document defines a set of cipher suites to add client credential protection to the Transport Layer Security (TLS) protocol. By negotiating one of those ciphersuites, the TLS clients will be able to determine for themselves when, how, to what extent and for what purpose information about them is communicated to others. The ciphersuites defined in this document can be used only when public key certificates are used in the client authentication process. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on September 28, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must Badra & Hajjeh Expires September 28, 2012 [Page 1] Internet-Draft Credential Protection Ciphersuites March 2012 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions Used in This Document . . . . . . . . . . . . . 3 2. The Credential Protection Ciphersuites . . . . . . . . . . . . 3 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 6.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Badra & Hajjeh Expires September 28, 2012 [Page 2] Internet-Draft Credential Protection Ciphersuites March 2012 1. Introduction TLS client credential protection may be done by a signalling mechanism based on a set of cipher suites as described in [Hajjeh]. This document specifies a set of cipher suites to add client credential protection to the TLS protocol. These cipher suites reuse existing key exchange algorithms with certificate-based authentication, and reuse existing cipher and MAC algorithms from [RFC5246], [RFC5288], and [RFC5932]. 1.1. Conventions Used in This Document 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]. 2. The Credential Protection Ciphersuites The name of cipher suites defined in this document includes the text "CP" to refer to the client credential protection. An example is shown below. CipherSuite Key Exchange Cipher Hash TLS_CP_RSA_WITH_AES_128_CBC_SHA RSA AES_128_CBC SHA1 The client indicates its willingness to protect its credentials by including one or more ciphersuites described here in the ClientHello.cipher_suites. These cipher suites MUST be placed at the top of the cipher suite list. When one of the cipher suites defined through this document is negotiated, the client MUST send the ChangeCipherSpec message before the Certificate and the CertificateVerify messages and after the ClientKeyExchange message. Badra & Hajjeh Expires September 28, 2012 [Page 3] Internet-Draft Credential Protection Ciphersuites March 2012 Client Server ClientHello --------> ServerHello Certificate CertificateRequest <-------- ServerHelloDone ClientKeyExchange ChangeCipherSpec ChangeCipherSpec <-------- Finished Certificate CertificateVerify Finished --------> Application Data <-------> Application Data If no certificates are available, the client MUST NOT include any credential protection cipher suite in the ClientHello.cipher_suites. If the server selects a cipher suite with client credential protection, the server MUST send a certificate appropriate for the negotiated cipher suite's key exchange algorithm, and MUST request a certificate from the client. If the server, agreeing on using a credential protection cipher suite, does not receive a client certificate in response to the subsequent certificate request, then it MUST abort the session by sending a fatal handshake failure alert. The client certificate MUST be appropriate for the negotiated cipher suite's key exchange algorithm, and any negotiated extensions. Current TLS specifications note that if the client certificate already contains a suitable DH or ECDH public key, then Yc is implicit and does not need to be sent again and consequently, the client key exchange message will be sent, but it MUST be empty. Even if the client key exchange message is used to carry the Yc, using the same Yc will allow traceability. Consequently, static Diffie-Hellman SHOULD NOT be used with this document. 3. Security Considerations The security considerations described throughout [RFC5246] apply here as well. Active attackers can modify messages and insert, remove, or replace cipher suites. An attacker could attempt to get the peers to negotiate a cipher suite that does not provide client credential protection. However, actives attacks and eavesdroppers are Badra & Hajjeh Expires September 28, 2012 [Page 4] Internet-Draft Credential Protection Ciphersuites March 2012 impossible here because the client MUST terminate the connection immediately upon failure to receive a valid Finished from the server without sending the Certificate and CertificateVerify messages. Such clients MUST generate a fatal "decrypt_error" alert prior to terminating the connection. In order for the client to be protected against man-in-the-middle attacks, the client SHOULD verify that the server provided a valid certificate and that the received public key belongs to the server. Because the question of whether this is the correct certificate is outside of TLS, applications that do implement credential protection cipher suites SHOULD enable the client to carefully examine the certificate presented by the server to determine if it meets its expectations. Particularly, the client MUST check its understanding of the server hostname against the server's identity as presented in the server Certificate message. In the absence of an application profile specifying otherwise, the matching is performed according to the following rules: o The client MUST use the server hostname it used to open the connection (or the hostname specified in the TLS "server_name" extension [RFC6066]) as the value to compare against the server name as expressed in the server certificate. The client MUST NOT use any form of the server hostname derived from an insecure remote source (e.g., insecure DNS lookup). CNAME canonicalization is not done. o If a subjectAltName extension of type dNSName is present in the certificate, it MUST be used as the source of the server's identity. o Matching is case-insensitive. o A "*" wildcard character MAY be used as the left-most name component in the certificate. For example, *.example.com would match a.example.com, foo.example.com, etc., but would not match example.com. o If the certificate contains multiple names (e.g., more than one dNSName field), then a match with any one of the fields is considered acceptable. If the match fails, the client MUST either ask for explicit user confirmation or terminate the connection and indicate the server's identity is suspect. Badra & Hajjeh Expires September 28, 2012 [Page 5] Internet-Draft Credential Protection Ciphersuites March 2012 Additionally, the client MUST verify the binding between the identity of the server to which it connects and the public key presented by this server. The client SHOULD implement the algorithm in Section 6 of [RFC5280] for general certificate validation, but MAY supplement that algorithm with other validation methods that achieve equivalent levels of verification (such as comparing the server certificate against a local store of already-verified certificates and identity bindings). If the client has external information as to the expected identity of the server, the hostname check MAY be omitted. It will depend on the application whether or not the server will have external knowledge of what the client's identity ought to be and what degree of assurance it needs to obtain of it. In any case, the server typically will have to check that the client has a valid certificate chained to an application-specific trust anchor it is configured with, following the rules of [RFC5280], before it successfully finishes the TLS handshake. One widely accepted layering principle is to decouple service authorization from client authentication on access. We therefore recommend that authorization decisions be performed and communicated at the application layer after the TLS handshake has been completed. 4. IANA Considerations This section provides guidance to the IANA regarding registration of values related to the credential protection cipher suites. CipherSuite TLS_CP_RSA_WITH_RC4_128_MD5 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_RC4_128_SHA = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_3DES_EDE_CBC_SHA = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_AES_128_CBC_SHA = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_AES_256_CBC_SHA = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_AES_128_CBC_SHA256 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_AES_256_CBC_SHA256 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_CAMELLIA_128_CBC_SHA = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_CAMELLIA_256_CBC_SHA = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_CAMELLIA_128_CBC_SHA256 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_CAMELLIA_256_CBC_SHA256 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_CAMELLIA_128_GCM_SHA256 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_CAMELLIA_256_GCM_SHA384 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_ARIA_128_CBC_SHA256 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_ARIA_256_CBC_SHA384 = { 0xXX,0xXX }; CipherSuite TLS_CP_RSA_WITH_ARIA_128_GCM_SHA256 = { 0xXX,0xXX }; Badra & Hajjeh Expires September 28, 2012 [Page 6] Internet-Draft Credential Protection Ciphersuites March 2012 CipherSuite TLS_CP_RSA_WITH_ARIA_256_GCM_SHA384 = { 0xXX,0xXX }; 5. Acknowledgements In August 2000, Francisco Corella proposed adding client credential protection to TLS by changing the order of TLS messages. This document borrows text from [Hajjeh]. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B. Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS)", RFC 4492, May 2006. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, August 2008. [RFC5932] Kato, A., Kanda, M., and S. Kanno, "Camellia Cipher Suites for TLS", RFC 5932, June 2010. 6.2. Informative References [I-D.hajjeh-tls-identity-protection] Hajjeh, I. and M. Badra, "Credential Protection Ciphersuites for Transport Layer Security (TLS)", draft-hajjeh-tls-identity-protection-09 (work in progress), November 2009. Badra & Hajjeh Expires September 28, 2012 [Page 7] Internet-Draft Credential Protection Ciphersuites March 2012 Authors' Addresses Mohamad Badra DU Email: mbadra@gmail.com Ibrahim Hajjeh INEOVATION Email: ibrahim.hajjeh@ineovation.com Badra & Hajjeh Expires September 28, 2012 [Page 8]