TCPM WG J. Touch Internet Draft USC/ISI Intended status: Standards Track March 19, 2014 Expires: September 2014 A TCP Authentication Option Extension for Payload Encryption draft-touch-tcp-ao-encrypt-00.txt Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This document may not be modified, and derivative works of it may not be created, except to publish it as an RFC and to translate it into languages other than English. 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 September 19, 2014. Copyright Notice Copyright (c) 2014 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 include Simplified BSD License text as described in Touch Expires September 19, 2014 [Page 1] Internet-Draft TCP-AO NAT Extension March 2014 Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract This document describes an extension to the TCP Authentication Option (TCP-AO) to encrypt the TCP segment payload in addition to providing TCP-AO's authentication of the payload, TCP header, and IP pseudoheader. This extension changes how the packet contents and headers are processed and which keys are derived, but not its key coordination or protection of long-lived connections. Table of Contents 1. Introduction...................................................2 2. Conventions used in this document..............................3 3. Background.....................................................3 4. Extension for Payload Encryption...............................3 4.1. Additional Master Key Tuple components....................3 4.2. Additional traffic keys...................................4 4.3. Per-Connection TCP-AO Parameters..........................4 4.4. Traffic Encryption Key Derivation Functions...............4 5. TCP-AO-ENC Interaction with TCP................................5 5.1. Sending TCP Segments......................................5 5.2. Receiving TCP Segments....................................5 5.3. Other TCP Impact..........................................5 6. Security Considerations........................................5 7. To be completed................................................6 8. IANA Considerations............................................6 9. References.....................................................6 9.1. Normative References......................................6 9.2. Informative References....................................6 10. Acknowledgments...............................................7 1. Introduction This document describes an extension to the TCP Authentication Option (TCP-AO) [RFC5925] called TCP-AO-ENC to support its use to encrypt TCP segment payload contents in addition to authenticating the segment. TCP-AO-ENC is intended for use where TCP user data privacy is required and where TCP control protocol protection is also needed. This document assumes detailed familiarity with TCP-AO [RFC5925]. TCP-AO-ENC extends how TCP-AO generates traffic keys and how those Touch Expires September 19, 2014 [Page 2] Internet-Draft TCP-AO NAT Extension March 2014 keys are used to process TCP segment headers and payloads, but does not otherwise alter the TCP-AO mechanism [RFC5926]. 2. 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 RFC-2119 [RFC2119]. When used in lower case, these words have their conventional meaning and do not convey the interpretations in RFC-2119. 3. Background The premise of TCP-AO-ENC is that it might be useful to allow TCP-AO to encrypt TCP segment payloads, in addition to authenticating the entire segment. This is accomplished by the following additions, as a preview: o An encryption flag to indicate when segment payload encryption is used. o Traffic encryption key, in addition to the TCP-AO traffic (authentication) key. TCP-AO-ENC can be used with only symmetric ciphers that avoiding the need for padding (stream ciphers). o Augment input and output processing to include encryption/decryption. TCP-AO-ENC does not change any other aspects of TCP-AO [RFC5925], and is compatible with TCP-AO-NAT [RFC6978]. TCP-AO-NAT is intended for use only where coordinated between endpoints for connections that match the shared MKT parameters, as with all other MKT parameters. 4. Extension for Payload Encryption The following describe the additions to TCP-AO needed to support TCP-AO-ENC. 4.1. Additional Master Key Tuple components TCP-AO-ENC augments the MKT as follows; as with other MKT components, these MUST NOT change during a connection: o TCP encryption flag. When present, this indicates the use of segment payload encryption. Touch Expires September 19, 2014 [Page 3] Internet-Draft TCP-AO NAT Extension March 2014 o Encryption Key Derivation Function (E-KDF). Indicates the key derivation function and its parameters, as used to generate traffic encryption keys from master keys in the same way that the TCP-AO KDG generates traffic (authentication) keys. o Encryption algorithm. Indicates the encryption algorithm and its parameters as used for encrypted connections. PTCP-AO-ENC processes TCP packets in the same way as TCP-AO, except that it replaces the authentication input and output processing as follows: 4.2. Additional traffic keys TCP-AO-ENC uses the E-KDF to derive four additional keys used for traffic encryption: o Send_SYN_traffic_encryption_key o Receive_SYN_traffic_encryption_key o Send_other_traffic_encryption_key o Receive_other_traffic_encryption_key 4.3. Per-Connection TCP-AO Parameters The per-connection TCP-AO parameters are not affected by the use of TCP-AO-ENC, except that MKTs indicated by Current_key and Rnext_key would indicate the use of payload encryption. The use of payload encryption as specified in these MKTs SHOULD NOT change during a TCP connection. 4.4. Traffic Encryption Key Derivation Functions Traffic encryption keys are derived from the MKTs using the E-KDF, in the same way and used on the same segments as their corresponding authentication keys, e.g.: o Send_SYN_traffic_encryption_key / Send_SYN_traffic_key o Receive_SYN_traffic_encryption_key / Receive_SYN_traffic__key o Send_other_traffic_encryption_key / Send_other_traffic__key o Receive_other_traffic_encryption_key / Receive_other_traffic_key Touch Expires September 19, 2014 [Page 4] Internet-Draft TCP-AO NAT Extension March 2014 5. TCP-AO-ENC Interaction with TCP TCP-AO-ENC augments TCP segment send and receive processing to include encryption/decryption. Note that the encryption initialization vector MAY depend on TCP header state, but MUST NOT depend on the processing of previous segments because segments may arrive (and need to be decrypted) out of order. 5.1. Sending TCP Segments Outgoing TCP segments are processed as follows: 1. The segment payload is encrypted in-place using the traffic encryption key. 2. The segment is authenticated using TCP-AO as per [RFC5925]. 5.2. Receiving TCP Segments Incoming TCP segments are processed as follows: 1. TCP-AO authenticates the segment, including discarding it if authentication fails, as per [RFC5925]. 2. The segment payload is decrypted in-place using the traffic encryption key. 5.3. Other TCP Impact TCP-AO-ENC has no impact on TCP beyond that of TCP-AO, including impact on TCP header size, connectionless resets, and ICMP handling. TCP-AO-ENC is compatible with the use of TCP-AO-NAT if traversal of NAT boxes is desired. 6. Security Considerations TCP-AO-ENC augments TCP-AO to provide segment payload privacy. TCP-AO-ENC relies on TCP-AO's authentication to avoid replay attacks and to ensure that the segments originate from the intended source. TCP-AO-ENC supports only stream ciphers because the TCP segment must be encrypted and decrypted in-situ. Support for padding would require additional option space to indicate the original message length, and this complication does not seem necessary. Touch Expires September 19, 2014 [Page 5] Internet-Draft TCP-AO NAT Extension March 2014 The design of TCP-AO-ENC can support either symmetric or asymmetric keys. However, because TCP-AO derives traffic (authentication) keys from MKTs using KDFs, it was deemed sufficient that TCP-AO-ENC derive traffic encryption keys from MKTs using E-KDFs in a similar manner, and both endpoints would thus derive the same traffic encryption keys just as they derive the same traffic (authentication) keys. Extensions of TCP-AO-ENC to support asymmetric keying are possible if traffic keys are managed using an out-of-band mechanism, but not if they are derived from MKTs. 7. To be completed... Where are required algorithms specified? This doc or a separate one? o E-KDF - also, can a MKT use the same alg for KDF and E-KDF? o Encryption algorithm - possibilities include AES CTR (CTR initial value can be the ESN) or AES CBC and Camellia CBC as per TLS 1.2. 8. IANA Considerations (TO BE CONFIRMED, BUT FOR NOW:) There are no IANA considerations for this document. This section can be removed upon publication as an RFC. 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. [RFC5925] Touch, J., A. Mankin, R. Bonica, "The TCP Authentication Option", RFC 5925, Jun. 2010. [RFC5926] Lebovitz, G., E. Rescorla, "Cryptographic Algorithms for the TCP Authentication Option (TCP-AO)", RFC 5926, June 2010. 9.2. Informative References [RFC6978] Touch, J., "A TCP Authentication Option Extension for NAT Traversal", RFC 6978, July 2013. Touch Expires September 19, 2014 [Page 6] Internet-Draft TCP-AO NAT Extension March 2014 10. Acknowledgments This extension was informed by discussions with Gene Tsudik. This document was prepared using 2-Word-v2.0.template.dot. Author's Address Joe Touch USC/ISI 4676 Admiralty Way Marina del Rey, CA 90292 USA Phone: +1 (310) 448-9151 Email: touch@isi.edu Touch Expires September 19, 2014 [Page 7]