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22-27. Additional Chapters

This file contains chapters 22-27 of RFC 3261:

    1. Usage of HTTP Authentication
    1. S/MIME
    1. Examples
    1. Augmented BNF for the SIP Protocol
    1. Security Considerations
    1. IANA Considerations

For the complete content of these chapters, please refer to the official RFC 3261 document at ````https://www.rfc-editor.org/rfc/rfc3261.txt\````.

22. Usage of HTTP Authentication​

SIP provides a stateless, challenge-based mechanism for authentication that is based on authentication in HTTP. Any time that a proxy server or UA receives a request, it MAY challenge the initiator of the request to provide assurance of its identity.

22.1 Framework​

The framework for SIP authentication closely parallels that of HTTP (RFC 2617). In particular, the BNF for auth-scheme, auth-param, challenge, realm, realm-value, and credentials is identical.

22.2 User-to-User Authentication​

When a UAS receives a request from a UAC, the UAS MAY authenticate the originator before the request is processed.

22.3 Proxy-to-User Authentication​

Similarly, when a proxy receives a request, it MAY authenticate the sender before the request is processed.

22.4 The Digest Authentication Scheme​

The Digest Authentication scheme is based on a simple challenge-response paradigm.

23. S/MIME​

S/MIME, short for Secure/Multipurpose Internet Mail Extensions, is a standard for public key encryption and signing of MIME data.

24. Examples​

This section contains numerous examples of SIP message exchanges.

25. Augmented BNF for the SIP Protocol​

This section provides the complete BNF grammar for SIP messages.

26. Security Considerations​

26.1 Attacks and Threat Models​

This section describes various security threats to SIP.

26.2 Security Mechanisms​

This section describes security mechanisms available for SIP.

26.3 Implementing Security Mechanisms​

This section provides guidelines for implementing security in SIP.

26.4 Limitations​

This section describes limitations of the security mechanisms.

26.5 Privacy​

This section discusses privacy considerations in SIP.

27. IANA Considerations​

This section describes IANA registrations for SIP-related values.

Note: For complete details of these chapters, including all subsections, examples, and technical specifications, please refer to the official RFC 3261 document.