Internet Engineering Task Force I. Hajjeh INTERNET DRAFT A. Serhrouchni ENST Paris M. Badra, Ed. O. Cherkaoui UQAM University Expires: June 2005 January 09, 2005 TLS Sign Status By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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 Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract TLS protocol provides authentication and data protection for communication between two entities. However, missing from the protocol is a way to perform non-repudiation service. This document defines extensions to the TLS protocol to allow it to perform non-repudiation service. It is based on [TLSSign] and it provides the client and the server the ability to sign by TLS, handshake and applications data using certificates such as X.509. Hajjeh, et. al. Informational - Expires June 2005 [Page 1] INTERNET-DRAFT TLS Sign January 2005 Table of Contents Abstract...........................................................1 1 Introduction.....................................................2 1.2 Requirements language..........................................3 2 TLS Sign overview................................................3 2.1 Signed data Record type.....................................5 2.1.1 TLS Sign activate/deactivate..............................5 2.1.1 TLS sign packet format....................................5 2.2 Storing signed data.........................................6 Security Considerations............................................7 References.........................................................7 Author's Addresses.................................................8 1 Introduction Actually, TLS is the most deployed security protocol for securing exchanges. It provides end-to-end secure communications between two entities with authentication and data protection. However, what is missing from the protocol is a way to provide the non-repudiation service. This document describes how the non-repudiation service may be integrated as an optional module in TLS. This is in order to provide both parties with evidence that the transaction has taken place and to offer a clear separation with application design and development. TLS-Sign's design motivations included: o TLS is application protocol-independent. Higher-level protocol can operate on top of the TLS protocol transparently. o TLS is a modular nature protocol. Since TLS is developed in four independent protocols, the approach defined in this document can be added by extending the TLS protocol and with a total reuse of pre-existing TLS infrastructures and implementations. o Several applications like E-Business require non-repudiation proof of transactions. It is critical in these applications to have the non-repudiation service that generates, distributes, validates and maintains the evidence of an electronic transaction. Since TLS is widely used to secure these applications exchanges, the non-repudiation should be offered by TLS. o Generic Non repudiation with TLS. TLS SIGN provides a generic non-repudiation service that can be easily used with protocols. TLS SIGN minimizes both design and implementation of the signature service and that of the designers and implementators who wish to use this module. Hajjeh, et. al. Informational - Expires June 2005 [Page 2] INTERNET-DRAFT TLS Sign January 2005 1.2 Requirements language The key words "MUST", "SHALL", "SHOULD", and "MAY", in this document are to be interpreted as described in RFC-2119. 2 TLS Sign overview TLS Sign is integrated as a higher-level module of the TLS Record protocol. It is optionally used if the two entities agree. This is negotiated by extending Client and Server Hello messages in the same way defined in [TLSExt]. In order to allow a TLS client to negotiate the TLS Sign, a new extension type should be added to the Extended Client and Server Hellos messages. TLS clients and servers may include an extension of type 'signature' in the Extended Client and Server Hellos messages. The 'extension_data' field of this extension contains a 'signature_request' where: enum { pkcs7(0), smime(1), xmldsig(2), (255); } ContentFormat; struct { ContentFormat content_format; SignMethod sign_meth; Signature_type sign_type<1..2^16-1>; } signature_request; enum { ssl_client_auth_cert(0), ssl_client_auth_cert_url(1), (255); } SignMethod; opaque Signature_type<1..2^16-1>; The client initiates the TLS Sign module by sending the ExtendedClientHello including the 'signature' extension. This extension contains: - the signature type (e.g., non-repudiation with proof of origin), - the content format (e.g., PKCS7 [PKCS7], S/MIME [S/MIME], XMLDSIG [XMLDSIG]), - the signature method (e.g. X509 authentication certificate). Actually, this document uses the same certificate used in client authentication. Any new signature method MAY be added in future versions (e.g. delegated attributes certificates). The server MAY reject the connection by sending the error alert "unsupported_extension" [TLSExt] and closing the connection. Hajjeh, et. al. Informational - Expires June 2005 [Page 3] INTERNET-DRAFT TLS Sign January 2005 If the server has an interest in getting non-repudiation data from the client and that the cipher_suites list sent by the client does not include any cipher_suite with signature ability, the server MUST close the connection by sending a fatal error. If the server has an interest in getting non-repudiation data from the client and that the cipher_suites list sent by the client includes at least a cipher_suite with signature ability, the server MUST select a cipher_suite with signature ability and MUST provide a certificate (e.g., RSA) that MAY be used for key exchange. Further, the server MUST request a certificate from the client with signing ability in the certificate request message (e.g., an RSA or a DSS signature-capable certificate). This request however, MUST be appropriate for the selected cipher suite. If the server has no interest in getting non-repudiation data from the client, the server will select a cipher_suite or, if no acceptable choices are presented, return a handshake failure alert and close the connection [TLS]." However, the client MAY demand a non-repudiation data without having a certificate. In this case, the client MAY reject the connection if the server is not ready to give it the non-repudiation service. This may be done using the signature type field of the signature_request structure. Client Server ------ ------ ClientHello --------> ServerHello Certificate ServerKeyExchange* CertificateRequest <-------- ServerHelloDone Certificate ClientKeyExchange CertificateVerify ChangeCipherSpec Finished --------> ChangeCipherSpec <-------- Finished (Signed) Application Data <-------> (Signed) App. Data Hajjeh, et. al. Informational - Expires June 2005 [Page 4] INTERNET-DRAFT TLS Sign January 2005 2.1 Signed data Record type New record type is added in this document: the signed data protocol. The message consists of a single byte of value 1 or 0. enum { change_cipher_spec(20), alert(21), handshake(22), application_data(23), tls_sign(25), (255) } ContentType; struct { enum { tls_sign_off(0), tls_sign_on(1), (255) } type; } TLSSignOnOff; 2.1.1 TLS Sign activate/deactivate To manage the generation of evidence, new record protocol is added by this document, called tls_sign_on_off. This protocol consists of a single message that is encrypted and compressed under the established connection state. Thus, no man in the middle can replay or inject this message. It consists of a Boolean of value 1 (tls_sign_on) or 0 (tls_sign_off). The tls_sign_on_off message is sent by both the client and server to notify the receiving party that subsequent records will carry data under the negotiated parameters and keys. If the client was not authenticated in his first TLS exchange or does not support a signature algorithm, the server who receives tls_sign_on_off message, MAY answer by signed data, ignore it or MAY invite the client to start a new TLS session sending the HelloRequest message. This message can be sent at any point after the TLS session has been established. 2.1.1 TLS sign packet format This document defines a new packet format that encapsulates signed data. The packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Content-Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Signed Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Content-Type Hajjeh, et. al. Informational - Expires June 2005 [Page 5] INTERNET-DRAFT TLS Sign January 2005 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |A D R R R R R R| +-+-+-+-+-+-+-+-+ A = acknowledgement of receipt D = signed data R = Reserved When the whole signed data is delivered to the receiver, the TLS Sign will check the signature. If the signature is valid and that the sender requires a proof of receipt, the receiver MUST generate a message with Type=A (acknowledgement of receipt), and as data-field the digest of the whole data. The data-field is of course signed by the receiver before it is sent to the sender. 2.2 Storing signed data The objective of TLS Sign is to provide both parties with evidence that can be stored and later presented to a third party to resolve disputes that arise if and when a communication is repudiated by one of the entities involved. This document provides the two basic types of non-repudiation service: o Non-repudiation with proof of origin: provides the TLS server with evidence proving that the TLS client has sent it the signed data at a certain time. o Non-repudiation with proof of delivery: provides the TLS client with evidence that the server has received the client's signed data at a specific time. TLS Handshake exchanges the current time and date according to the entities internal clock. Thus, the time and date can be stored with the signed data as a proof of communication. For B2C or B2B transactions, non-repudiation with proof of origin and non- repudiation with proof of receipt are both important. If the TLS client requests a non-repudiation service with proof of receipt, the server SHOULD verify and send back to client a signature on the hash of signed data. The following figure explains the different events for proving and storing signed data [RFC2828]. RFC 2828 uses the term "critical action" to refer to the act of communication between the two entities. For a complete non-repudiation deployment, 6 phases should be respected: Hajjeh, et. al. Informational - Expires June 2005 [Page 6] INTERNET-DRAFT TLS Sign January 2005 -------- -------- -------- -------- -------- . -------- Phase 1: Phase 2: Phase 3: Phase 4: Phase 5: . Phase 6: Request Generate Transfer Verify Retain . Resolve Service Evidence Evidence Evidence Evidence . Dispute -------- -------- -------- -------- -------- . -------- Service Critical Evidence Evidence Archive . Evidence Request => Action => Stored => Is => Evidence . Is Is Made Occurs For Later Tested In Case . Verified and Use | ^ Critical . ^ Evidence v | Action Is . | Is +-------------------+ Repudiated . | Generated |Verifiable Evidence|------> ... . ----+ +-------------------+ 1- Requesting explicit transaction evidence before sending data. Normally, this action is taken by the SSL/TLS client 2- If the server accepts, the client will generate evidence by signing data using his X.509 authentication certificate. Server will go through the same process if the evidence of receipt is requested. 3 - The signed data is then sent by the initiator (client or server) and stored it locally, or by a third party, for a later use if needed. 4 - The entity that receive the evidence process to verify the signed data. 5- The evidence is then stored by the receiver entity for a later use if needed. 6- In this phase, which occurs only if the critical action is repudiated, the evidence is retrieved from storage, presented, and verified to resolve the dispute. With this method, the stored signed data (or evidence) can be retrieved by both parties, presented and verified if the critical action is repudiated. Security Considerations Security issues are discussed throughout this memo. References [TLS] Dierks, T., et. al, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [TLSExt] Blake-Wilson, S., et. al, "Transport Layer Security (TLS) Extensions", RFC 3546, June 2003. Hajjeh, et. al. Informational - Expires June 2005 [Page 7] INTERNET-DRAFT TLS Sign January 2005 [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax Standard," version 1.5, November 1993. [S/MIME] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC 2633, June 1999. [XMLDSIG]Eastlake, D., et. al, "(Extensible Markup Language) XML Signature Syntax and Processing", RFC 3275, March 2002. [TLSSign]Hajjeh, I., Serhrouchni, A., "Integrating a signature module in SSL/TLS, ICETEĈ2004, ACM/IEEE, First International Conference on E-Business and Telecommunication Networks, Portugal, August 2004. [RFC2828]Shirey, R., "Internet Security Glossary", RFC 2828, May 2000. Author's Addresses Ibrahim Hajjeh ENST 46 rue Barrault 75013 Paris Phone: NA France Email: Ibrahim.Hajjeh@enst.fr Ahmed serhrouchni ENST 46 rue Barrault 75013 Paris Phone: NA France Email: Ahmed.serhrouchni@enst.fr Mohamad Badra UQAM University Montreal (Quebec) Phone: NA Canada Email: Mohamad.Badra@uqam.ca Omar Cherkaoui UQAM University Montreal (Quebec) Phone: NA Canada Email: Omar.Cherkaoui@uqam.ca Acknowledgements The authors would like to thank Eric Rescorla for discussions and comments on the design of TLS Sign. 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 Hajjeh, et. al. Informational - Expires June 2005 [Page 8] INTERNET-DRAFT TLS Sign January 2005 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 IETF's procedures with respect to rights in IETF 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 (2004). 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. Hajjeh, et. al. Informational - Expires June 2005 [Page 9]