SIP Security

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SIP Security

• Matt Hsu

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Agenda

• SIP Security Overview
• SIP Security Mechanisms
• SIP Threat Models
• Summary
• Reference

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SIP Security Overview

• How to insure security for SIP call setup
• Register protection, DoS..
• NAT, Firewall Traversal of RTP Media packets

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SIP Security Mechanisms

• End-to-end mechanisms
• Basic authentication
• Digest authentication (similar to HTTP digest)
• Message body encryption using S/MIME
• Hop-by-hop mechanisms
• Transport Layer Security (TLS)
• IP Security (IPSec)
• The SIPS URI schema
• Security Mechanism Agreement for the Session
  Initiation Protocol (SIP) RFC 3329

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Basic authentication
Server
Client
INVITE

• Horribly Vulnerable to Replay Attack
• Cleartext Password
• Deprecated in New RFC

401 Authorize Yourself WWW-Authenticate Basic
realmmufasa
INVITE Authorization Basic QWxhZGRpbjpvcGVuI
200 OK
Base 64 encoded
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SIP Digest authentication
SIP Server
SIP Client
REQUEST
Generate the Nonce value
CHALLENGE
Nonce, realm
Compute response F(nonce, Username, password,
realm)
F MD5
REQUEST
Nonce, realm, Username, response
Authenticate compute F(nonce, username,
password, realm) And compare with response
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SIP Digest authentication

• This mechanism is borrowed from HTTP
  Authentication RFC 2617 but modified slightly
• Client Authentication
• No message integrity protection
• No confidentiality

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S/MIME
INVITE sipu_at_h SIP/2.0 From sipbob_at_foo To
sipa_at_c Content-Type multipart

• A IETF standard for email security
• Mutual authentication
• Payload integrity and confidentiality
• Big overhead

SDP
INVITE sipu_at_h SIP/2.0 From sipbob_at_foo To
sipa_at_c Content-Type SDP SDP text
signature
certificate
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IPSec

• Authentication and integrity
• Replay protection
• Supports TCP and UDP
• IKE barely supported
• Not usually integrated with SIP application
• Policy managed at the OS level

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TLS

• Authentication, integrity, confidentiality
• Replay protection
• Supports TCP only
• Resides in application layer
• Firewall and NAT Traversal

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SIPS URI Schema

• New URI schema
• SIPSuser_at_example.com

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Security Mechanism Agreement for the Session
Initiation Protocol (SIP)
Client List
Client
Server
Server List
Turn on security
Server List
Ok or Error
Security Agreement Message Flow
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SIP Threats Model

• Registration Hijacking
• Impersonating a server
• The server could be impersonated by an attacker
• Tampering with message bodies
• Tearing down sessions
• Insert a BYE message
• Denial of Service attacks

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Summary

• CPL-SL (in master thesis) could solve some SIP
  security threats

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Reference

• SIP Security Agreement RFC 3329
• SIP Security Mechanisms Update, Ben Campbell
• An overview of SIP Security, Samir Chatterjee