NETCONF Working Group Mohamad Badra Internet Draft LIMOS Laboratory Intended status: Standards Track
February 15,May 27, 2008 Expires: AugustNovember 2008 NETCONF over Transport Layer Security (TLS) draft-ietf-netconf-tls-01.txtdraft-ietf-netconf-tls-02.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 August 15,November 27, 2008. 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...................................................2Introduction...................................................3 1.1. Conventions used in this document.........................2document.........................3 2. NETCONF over TLS...............................................3 2.1. Connection Initiation.....................................3 2.2. Connection Closure........................................3Closure........................................4 3. Endpoint Authentication and Identification.....................4 3.1. Server Identity...........................................4Identity...........................................5 3.2. Client Identity...........................................5Identity...........................................6 3.3. Password-Based Authentication.............................5Authentication.............................6 4. Cipher Suite Requirements......................................7 5. Security Considerations........................................7 6. IANA Considerations............................................7 7. Acknowledgments................................................7 8. References.....................................................7 8.1.Acknowledgments................................................8 A. Appendix - Test Vectors for the PSK Derivation Function........9 B. Appendix - Enabling Third Party Authentication using Passwords10 B.1. Working Group discussion at the 71st IETF meeting........12 Normative References......................................7 Author's Addresses................................................8References.............................................13 Authors' Addresses...............................................14 Intellectual Property Statement...................................8 Disclaimer of Validity............................................9and Copyright Statements...................14 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] 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 [NETNOT],[I-D.ietf-- netconf-notification], 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 processes a closure request ofcloses 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 some othera fatal alerterror has been transmitted,occurred, each party is required to send a close_notify alert before closing the write side of the connection.connection [RFC4346]. 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 in TLSauthentication, which can be based on either preshared keys [RFC4279] or public key certificates [RFC4346]. 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. 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 [RFC3280][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-Based 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 password also provide functionality for generating a new random password, taking [RFC4086] into account. This document generates the PSK from the password as follow: PSK = SHA-1(SHA-1(password + psk_identitySHA-1(SHA-1(psk_identity + "Key Pad for Netconf")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_hint can do double duty and also provide a form of server authentication in the case where the user has the same password on a number of NETCONF servers. 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 passwords 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 SHA- 1(SHA-1(passwordthe inner SHA-1 (SHA-1(SHA-1(password + psk_identity + "Key Pad for Netconf") + psk_identity_hint),psk_identity_hint)), 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, the management interface by which 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 encoding of the password. The management interface MAY accept other encodings if the algorithm for translating the encoding to a binary string is specified. 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] and [RFC4279] apply here as well. As with all schemes involving shared keys and passwords, special care should be taken to protect the shared values and passwords as well as to limit their 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 this documentSection 3.1 was lifted from [RFC4642]. The author would like to acknowledge David Harrington, Miao Fuyou, Eric Rescorla, Juergen SchoenwaelderSchoenwaelder, Simon Josefsson, Olivier Coupelon and the NETCONF mailing list members for their comments on the document. The author appreciates also Bert WijnenWijnen, Mehmet Ersue and Dan Romascanu for their efforts on issues resolving discussion, and Charlie Kaufman for the thorough review of this document and for the helpful comments on the password-based authentication. 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. [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. [RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness RequirementsA. Appendix - Test Vectors for Security", BCP 106, RFC 4086, June 2005. [RFC4279] Eronen, P. and H. Tschofenig., "Pre-Shared Key Ciphersuitesthe PSK Derivation Function The test vectors 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)the PSK derivation function in this document have been cross-verified by two independent implementations. An implementation that concurs 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, "Usingthe NETCONF Configuration Protocol over Secure Shell (SSH)", RFC 4742, December 2006. [NETNOT] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", draft-ietf-netconf-notification-11.txt, (workresults provided in progress), November 2007. Author's Addresses Mohamad Badra LIMOS Laboratory - UMR6158, CNRS France Email: firstname.lastname@example.org 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(password + psk_identity + "Key Pad for Netconf") == 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 b6540344 B. Appendix - Enabling Third Party Authentication using Passwords During the 71st IETF meeting, several proposals have been proposed to enable third party authentication that could be used in combination with existing user authentication databases such as RADIUS. They are listed below. More details on those proposals may be found at https://www3.ietf.org/proceedings/08mar/slides/netconf-1/netconf- 1.htm and http://www.psg.com/lists/netconf/netconf.2008/msg00125.html. We summarize them as following: 1. Defining <user-login> RPC: -------------------------- This option relies on JUNOS mechanism to enable an authentication function via third parties. It consists of establishing a TLS with no manager authentication, leaving the <request-login> RPC as the only valid RPC. Anything else is an error. Once the TLS session is established, the agent MUST authenticate the manager by emitting the following <rpc> tag element: <rpc-reply message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"> <challenge>Password:</challenge> </rpc-reply> In which the manager MUST reply with the following: <rpc> <request-login> <challenge-response>password</challenge-response> </request-login> </rpc> The rules to handle this were pretty simple: - The <request-login> RPC could only be performed if the session wasn't authenticated. - No other RPCs could be performed if the session wasn't authenticated. - The transport protocol can authenticate the session (internally). Pros and cons: o is simple to do. But o might raise questions from the security ADs; NETCONF assumes the authentication is part of the transport not NETCONF. o only works for plaintext passwords (SASL PLAIN). 2. Enhancing TLS: -------------- The second option consists of extending TLS so the manager authentication becomes part of TLS. This extension, detailed in http://tools.ietf.org/id/draft-badra-tls-password-ext-01.txt, defines a new extension and a new TLS message to the TLS protocol to enable TLS client authentication using passwords. The extension is used to convey the manager login, whereas the new message is defined and sent by the manager to prove its knowledge of the password. Steps during the TLS negotiation: - The manager adds such an extension to its TLS ClientHello. - If the agent agrees on using this extension, it will notify the manager and replies with its certificate and/or its authenticated public key. - The manager generates a premaster secret and encrypts it using the agent public key. - The manager then computes the session key using the premaster secret and encrypts, among others, its password with the computed key. - The agent decrypts the premaster secret and computes the same key to decrypt the password. - The agent checks with a database (or AAA infrastructures) to verify the password and then to authenticate the manager. Pros and cons o is simple to do. But o It is indeed not easy to convince TLS WG to add password authentication extension to TLS. 3. Running BEEP over TLS: ---------------------- It looks complex for a solution, requires that all implementations do actually support BEEP. 4. Extending NETCONF with a message to start TLS: ---------------------------------------------- This option consists of extending NETCONF with a new message to start the TLS negotiation and to perform an authentication mechanism based on RFC4422 (SASL) or on any similar protocol. Pros and cons o simple to do. But o might raise questions from the security ADs; NETCONF assumes the authentication is part of the transport not NETCONF. Moreover, it adds complexity related to the use of SASL PLAIN. 5. Enable SSH (RFC4742 and TLS (as defined through this document: -------------------------------------------------------------- Since SSH already defines a password-based authentication and because this protocol MUST be implemented as a security protocol for NETCONF, users can rely on SSH for password authentication, and on TLS for authentication using PSK or certificates. This means the agent SHOULD passively listen for the incoming SSH (respectively TLS) connection on port 830 (respectively port <TBA-by-IANA>). Pros and cons o simple to do. o already specified by RFC4742 and by the current document. B.1. Working Group discussion at the 71st IETF meeting Some of the options have been found as not practical in the WG session during 71st meeting. Options #2 and #3 have not been supported in the WG session. Option #1 and # 4 seems to be against the security design for NETCONF. Whether #5 or other options can be accepted by the WG members needs to be discussed on the mailing list. 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, 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] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", draft-ietf-netconf-notification-12.txt, (work in progress), February 2008. Authors' Addresses Mohamad Badra LIMOS Laboratory - UMR6158, CNRS France Email: email@example.com Contributors Ibrahim Hajjeh INEOVATION France Email: firstname.lastname@example.org 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. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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