I-D ACTION:draft-ietf-sip-sec-agree-01.txt

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This draft is a work item of the Session Initiation Protocol Working Group of the IETF.

	Title		: Security Mechanism Agreement for SIP Sessions
	Author(s)	: J. Arkko et al.
	Filename	: draft-ietf-sip-sec-agree-01.txt
	Pages		: 16
	Date		: 13-May-02
	
SIP has a number of security mechanisms. Some of them have been built
in to the SIP protocol, such as HTTP authentication or secure
attachments. These mechanisms have even alternative algorithms and
parameters. SIP does not currently provide any mechanism for
selecting which security mechanisms to use over a connection. In
particular, even if some mechanisms such as OPTIONS were used to make
this selection, the selection would be vulnerable against the
Bidding-Down attack. This document defines three header fields for
negotiating the security mechanisms within SIP between a user agent
client and its next hop SIP entity. A SIP entity applying this
mechanism must always require some minimum security (i.e. integrity
protection) from all communicating parties in order to secure the
negotiation, but the negotiation can agree on which specific minimum
security is used.

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