NETCONF Working Group Mohamad Badra Internet Draft LIMOS Laboratory Intended status: Standards Track
June 5, 2008 Expires: DecemberSeptember 2, 2008 NETCONF over Transport Layer Security (TLS) draft-ietf-netconf-tls-03.txtdraft-ietf-netconf-tls-04.txt Status of this Memo 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 becomes aware will be disclosed, in accordance with 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 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 December 5, 2008.March 2, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract The Network Configuration Protocol (NETCONF) provides mechanisms to install, manipulate, and delete the configuration of network devices. This document describes how to use the Transport Layer Protocol (TLS) to secure NETCONF exchanges. Table of Contents 1. Introduction...................................................3 1.1. Conventions used in this document.........................3 2. NETCONF over TLS...............................................3 2.1. Connection Initiation.....................................3 2.2. Connection Closure........................................4 3. Endpoint Authentication and Identification.....................4 3.1. Server Identity...........................................5 3.2. Client Identity...........................................6 3.3. Password-BasedPre-shared key Authentication.............................6 4. Cipher Suite Requirements......................................7 5. Security Considerations........................................7 6. IANA Considerations............................................8Considerations............................................7 7. Acknowledgments................................................8 A. Appendix - Test Vectors for the PSK Derivation Function........9Acknowledgments................................................7 8. References.....................................................8 8.1. Normative References..............................................9 Authors' Addresses...............................................10 Intellectual Property Statement..................................10 Disclaimer of Validity...........................................11References......................................8 1. Introduction The NETCONF protocol [RFC4741] defines a simple mechanism through which a network device can be managed. NETCONF is connection- oriented, requiring a persistent connection between peers. This connection must provide reliable, sequenced data delivery, integrity and confidentiality and peers authentication. This document describes how to use TLS [RFC4346][RFC5246] to secure NETCONF connections. Throughout this document, the terms "client" and "server" are used to refer to the two ends of the TLS connection. The client actively opens the TLS connection, and the server passively listens for the incoming TLS connection. The terms "manager" and "agent" are used to refer to the two ends of the NETCONF protocol session. The manager issues NETCONF remote procedure call (RPC) commands, and the agent replies to those commands. When NETCONF is run over TLS using the mapping defined in this document, the client is always the manager, and the server is always the agent. 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 RFC-2119 [RFC2119]. 2. NETCONF over TLS Since TLS is application protocol-independent, NETCONF can operate on top of the TLS protocol transparently. This document defines how NETCONF can be used within a Transport Layer Security (TLS) session. 2.1. Connection Initiation The peer acting as the NETCONF manager MUST also act as the TLS client. It MUST connect to the server that passively listens for the incoming TLS connection on the IANA-to-be-assigned TCP port <TBA>. It MUST therefore send the TLS ClientHello to begin the TLS handshake. Once the TLS handshake has been finished, the client and the server MAY then send their NETCONF exchanges. In particular, the client will send complete XML documents to the server containing <rpc> elements, and the server will respond with complete XML documents containing <rpc-reply> elements. The client MAY indicate interest in receiving event notifications from a NETCONF server by creating a subscription to receive event notifications [I-D.ietf- netconf-notification],[RFC5277], in which the NETCONF server replies to indicate whether the subscription request was successful and, if it was successful, begins sending the event notifications to the NETCONF client as the events occur within the system. All these elements are encapsulated into TLS records of type "application data". These records are protected using the TLS material keys. Current NETCONF messages don't include a message's length. This document uses consequently the same delimiter sequence defined in [RFC4742] and therefore the special character sequence, ]]>]]>, to delimit XML documents. 2.2. Connection Closure Either NETCONF peer MAY stop the NETCONF connection at any time and therefore notify the other NETCONF peer that no more data on this channel will be sent and that any data received after a closure request will be ignored. This MAY happen when no data is received from a connection for a long time, where the application decides what "long" means. TLS has the ability for secure connection closure using the Alert protocol. When the NETCONF peer closes the NETCONF connection, it MUST send a TLS close_notify alert before closing the TCP connection. Any data received after a closure alert is ignored. Unless a fatal error has occurred, each party is required to send a close_notify alert before closing the write side of the connection [RFC4346].[RFC5246]. The other party MUST respond with a close_notify alert of its own and close down the connection immediately, discarding any pending writes. It is not required for the initiator of the close to wait for the responding close_notify alert before closing the read side of the connection. 3. Endpoint Authentication and Identification NETCONF requires that its transport provide mutual authentication of client and server, so cipher suites that are anonymous or which only authenticate the server to the client MUST NOT be used with NETCONF. This document specifies how to use TLS with endpoint authentication, which can be based on either preshared keys [RFC4279] or public key certificates [RFC4346].[RFC5246]. Some cipher suites (e.g. TLS_RSA_PSK_WITH_AES_128_CBC_SHA) use both. Section 3.1 describes how the client authenticates the server if public key certificates are provided by the server, section 3.2 describes how the server authenticates the client if public key certificates are provided by the client, and section 3.3 describes how the client and server mutually authenticate one another using a password.pre-shared key (PSK). 3.1. Server Identity During the TLS negotiation, the client MUST carefully examine the certificate presented by the server to determine if it meets their 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 order to prevent man-in-the-middle attacks. Matching is performed according to these rules [RFC4642]: - The client MUST use the server hostname it used to open the connection (or the hostname specified in TLS "server_name" extension [RFC4366]) 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. - If a subjectAltName extension of type dNSName is present in the certificate, it MUST be used as the source of the server's identity. - Matching is case-insensitive. - 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. - 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. Additionally, clients MUST verify the binding between the identity of the servers to which they connect and the public keys presented by those servers. Clients 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. 3.2. Client Identity Typically, the server has no external knowledge of what the client's identity ought to be and so checks (other than that the client has a certificate chain rooted in an appropriate CA) are not possible. If a server has such knowledge (typically from some source external to NETCONF or TLS) it MUST check the identity as described above. 3.3. Password-BasedPre-shared key Authentication [RFC4279] supports authentication based on pre-shared keys (PSKs). These pre-shared keys are symmetric keys, shared in advance among the communicating parties. The PSK can be generated in many ways and its length is variable. Implementation of this document MAY rely on [RFC4279] to enable password based user authentication. In this case, the password is used to generate the PSK.It is RECOMMENDED that implementations that allow the administrator to manually configure the passwordPSK also provide functionality for generating a new random password,PSK, taking [RFC4086] into account. This document generatesIf both the PSK fromclient and the password as follow: PSK = SHA-1(SHA-1(psk_identity + "Key Pad for Netconf" + password) + psk_identity_hint) Where + means concatenation. The label "Key Pad for Netconf" is an ASCII string. The psk_identity_hint is initially defined in section 5.1 of [RFC4279]. The psk_identity_hintserver agree on using the pre-shared key authentication, the server can do double duty and alsoprovide a form of server authentication"PSK identity hint" in the case where the user has the same password on a number of NETCONF servers.ServerKeyExchange message. If a hint is provided, the psk_identity_hint is encoded in the same way as in [RFC4279] and should be a string representation of the name of the server recognizable to the administrator or his software. In the case where the user types a server name to connect to, it should be that string. If the string the user enters differs from the one returned as psk_identity_hint, the software could display the server's name and ask the user to confirm. For automated scripts, the names could be expected to match. It is highly recommended that implementations set the psk_identity_hint to the DNS name of the NETCONF server (i.e., the TLS server). It is RECOMMENDED that users choose different passwordsPSKs for the different servers they manage. Note 1: The NETCONF over TLS implementation need not store the password in clear text, but rather can store the value of the inner SHA-1, (SHA-1(psk_identity + "Key Pad for Netconf" + password)), which could not be used as a password equivalent for applications other than NETCONF. Deriving the PSK from a password is not secure. This construction is used because it is anticipated that people will do it anyway. Note 2:[RFC4279] defines some conformance requirements for the PSK, for the PSK identity encoding and for the identity hint. The same requirements apply here as well; in particular on the password.Moreover, it describes the management interface by whichrequirements for entering the password is provided MUST accept ASCII strings of at least 64 octets and MUST NOT add a null terminator before using them as shared secrets. It MUST also accept a HEX encodingPSK and/or PSK identity (See Section 5 of the password. The management interface MAY accept other encodings if the algorithm[RFC4279] for translating the encoding toa binary string is specified.more detailed description of these requirements). Those same requirements apply here as well. 4. Cipher Suite Requirements A compliant implementation of the protocol specified in this document MUST implement the cipher suite TLS_DHE_PSK_WITH_AES_128_CBC_SHA and MAY implement any TLS cipher suite that provides mutual authentication. 5. Security Considerations The security considerations described throughout [RFC4346][RFC5246] and [RFC4279] apply here as well. This document in its current version doesn't support third party authentication due to the fact that TLS doesn't specify this way of authentication and that NETCONF depends on the transport protocol for the authentication service. If third party authentication is needed, BEEP or SSH transport can be used. As with all schemes involving shared keys and passwords,keys, special care should be taken to protect the shared values and passwordssecret as well as to limit theirits exposure over time. Alternatively, using certificates would provide better protection. 6. IANA Considerations IANA is requested to assign a TCP port number that will be the default port for NETCONF over TLS sessions as defined in this document. IANA has assigned port <TBA> for this purpose. 7. Acknowledgments A significant amount of the text in Section 3.1 was lifted from [RFC4642]. The author would like to acknowledge David Harrington, Miao Fuyou, Eric Rescorla, Juergen Schoenwaelder, Simon Josefsson, Olivier Coupelon and the NETCONF mailing list members for their comments on the document. The author appreciates also Bert Wijnen, Mehmet Ersue and Dan Romascanu for their efforts on issues resolving discussion, and Charlie KaufmanKaufman, Pasi Eronen and Tim Polk for the thorough review of this document and for the helpful comments on the password-based authentication. A. Appendix - Test Vectors for the PSK Derivation Function The test vectors for the PSK derivation function in this document have been cross-verified by two independent implementations. An implementation that concurs with the results provided in this document should be interoperable with other similar implementations. password = password psk_identity = psk_identity psk_identity_hint = psk_identity_hint The inner SHA-1 value (in hex): inner := SHA-1(psk_identity + "Key Pad for Netconf" + password) == SHA-1("psk_identityKey Pad for Netconfpassword") => 6d6eeb6a b8d0466b 45245d07 47d86726 b41b868c The outer SHA-1 value (in hex): outer := SHA-1(inner + psk_identity_hint) => 88f3824b 3e5659f5 2d00e959 bacab954 b6540344document. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. [RFC4086] Eastlake,[RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. [RFC4279] Eronen, P. and H. Tschofenig., "Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)", RFC 4279, December 2005. [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol 1.1", RFC 4346, April 2006.[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and T. Wright, "Transport Layer Security (TLS) Extensions", RFC 4366, April 2006. [RFC4642] Murchison, K., Vinocur, J., Newman, C., "Using Transport Layer Security (TLS) with Network News Transfer Protocol (NNTP)", RFC 4642, October 2006 [RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741, December 2006. [RFC4742] Wasserman, M. and T. Goddard, "Using the NETCONF Configuration Protocol over Secure Shell (SSH)", RFC 4742, December 2006. [I-D.ietf-netconf-notification][RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol 1.2", RFC5246, August 2008. [RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", draft-ietf-netconf-notification-13.txt, (work in progress),RFC 5277, July 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. Authors'Author's Addresses Mohamad Badra LIMOS Laboratory - UMR6158, CNRS France Email: email@example.com Contributors Ibrahim Hajjeh INEOVATION France Email: firstname.lastname@example.org Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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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, THE IETF TRUST 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 IETF Trust (2008). 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.