Protection of BGP Sessions via the TCP MD5 Signature Option
RFC 2385
Document | Type |
RFC - Proposed Standard
(August 1998; Errata)
Obsoleted by RFC 5925
Updated by RFC 6691
|
|
---|---|---|---|
Author | Andy Heffernan | ||
Last updated | 2017-09-28 | ||
Replaces | draft-heffernan-tcp-md5 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | WG Document | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 2385 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group A. Heffernan Request for Comments: 2385 cisco Systems Category: Standards Track August 1998 Protection of BGP Sessions via the TCP MD5 Signature Option Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. IESG Note This document describes currrent existing practice for securing BGP against certain simple attacks. It is understood to have security weaknesses against concerted attacks. Abstract This memo describes a TCP extension to enhance security for BGP. It defines a new TCP option for carrying an MD5 [RFC1321] digest in a TCP segment. This digest acts like a signature for that segment, incorporating information known only to the connection end points. Since BGP uses TCP as its transport, using this option in the way described in this paper significantly reduces the danger from certain security attacks on BGP. 1.0 Introduction The primary motivation for this option is to allow BGP to protect itself against the introduction of spoofed TCP segments into the connection stream. Of particular concern are TCP resets. To spoof a connection using the scheme described in this paper, an attacker would not only have to guess TCP sequence numbers, but would also have had to obtain the password included in the MD5 digest. This password never appears in the connection stream, and the actual form of the password is up to the application. It could even change Heffernan Standards Track [Page 1] RFC 2385 TCP MD5 Signature Option August 1998 during the lifetime of a particular connection so long as this change was synchronized on both ends (although retransmission can become problematical in some TCP implementations with changing passwords). Finally, there is no negotiation for the use of this option in a connection, rather it is purely a matter of site policy whether or not its connections use the option. 2.0 Proposal Every segment sent on a TCP connection to be protected against spoofing will contain the 16-byte MD5 digest produced by applying the MD5 algorithm to these items in the following order: 1. the TCP pseudo-header (in the order: source IP address, destination IP address, zero-padded protocol number, and segment length) 2. the TCP header, excluding options, and assuming a checksum of zero 3. the TCP segment data (if any) 4. an independently-specified key or password, known to both TCPs and presumably connection-specific The header and pseudo-header are in network byte order. The nature of the key is deliberately left unspecified, but it must be known by both ends of the connection. A particular TCP implementation will determine what the application may specify as the key. Upon receiving a signed segment, the receiver must validate it by calculating its own digest from the same data (using its own key) and comparing the two digest. A failing comparison must result in the segment being dropped and must not produce any response back to the sender. Logging the failure is probably advisable. Unlike other TCP extensions (e.g., the Window Scale option [RFC1323]), the absence of the option in the SYN,ACK segment must not cause the sender to disable its sending of signatures. This negotiation is typically done to prevent some TCP implementations from misbehaving upon receiving options in non-SYN segments. This is not a problem for this option, since the SYN,ACK sent during connection negotiation will not be signed and will thus be ignored. The connection will never be made, and non-SYN segments with options will never be sent. More importantly, the sending of signatures must be under the complete control of the application, not at the mercy of the remote host not understanding the option. Heffernan Standards Track [Page 2] RFC 2385 TCP MD5 Signature Option August 1998 3.0 Syntax The proposed option has the following format: +---------+---------+-------------------+ | Kind=19 |Length=18| MD5 digest... | +---------+---------+-------------------+ | | +---------------------------------------+ | |Show full document text