1. SIP &TLS
Security in a peer to peer world
Olle E. Johansson, oej@edvina.net, Fosdem 2016, january 30-31, Brussels
Twitter @oej

2. TLS IN ONE PICTURE
Server
Network
Link
Application
Client
Identity check
Algorithm agreement
Key Set up
Encryption of data
Without prior agreement
Certificate validation

3. A SIP REGISTRATION AND CALL
SIP client/server
(phone)
SIP serverHello, here’s my current location
SIP Contact URI
(IPv6 or IPv4 address + port)
Incoming callIncoming call
Contact
URI
Two separate
Connections/Flows

4. …WITHTLS
SIP client/server
(phone)
SIP server
Hello, here’s my current location
SIP Contact URI
(IPv6 or IPv4 address + port)
Incoming call
Incoming call
TLS
TLS
The phone needs
to be a TLS server with a
certificate
Contact
URI
The cert needs to match
the Contact URI.
Which is changing unless you use GRUU
Contact
URI

5. SIPS: - WAS A BAD IDEA.
Just forget it. SIP doesn’t work like the
web.And the web is also changing.

6. SIP MATCHING CERTIFICATE
sip:alice@example.com
SIP server
cn: example.com
san: ww.example.com
SIP server
cn: namn.se
san: example.com
SIP server
cn: example.com
DNS SRV for example.com points to
sip01.siphosting.com
FAIL
OK!OK!
SIP server
cn: *.example.com
Fail
Wildcards are
not allowed.
With no SAN, CN is used.
But only with no SAN.
RFC 5922 - SIP domain certificates

7. COMPARE WITH XMPP -
CONNECTION = “AVAILABLE”
XMPP client
XMPP
server
Incoming message
TLS
A client without a
connection is off line.
OneTCP/TLS connection.

8. SIP XMPP STYLE
= SIP OUTBOUND
SIP client/server
(phone)
SIP server
Incoming call
TLS
Reuse the same connection,
managed by the client!
REGISTER
INVITE
As long as we have at least
one connection, the UA is ”online”
and available.
RFC 5626

9. SIP OUTBOUND AND IP FLOWS
SIP
”it’s really hard to notice that aTCP connection is dead”
Panagiotis Stathopoulos at #Fosdem 2016
UA
SIP
SIP
SIP edge proxys
SIP location server

10. SECURITY?
NO GUARANTEES, EVER
SIP SIP
UA UA
You can only control and
verify the first hop

11. SIP PEER 2 PEER
SIP proxy
(man in the middle)

12. …WITH FORKING
The payload and message reach
everyone!

13. AND CONFERENCE CALLS

14. MY QUESTION:
A SECURE SESSION IS?
SIP proxy
(man in the middle)
SIP is a rendevous
protocol. We find each other and
establish a session.
Can we find a way to secure that
session and trust it?

15. MY QUESTION:
WHAT IS A SECURE SESSION?
SIP proxy
(man in the middle)
MSRP?
WebRTC Datachannels? This applies to webrtc,
XMPP, SIP and other
solutions…

16. IN SHORT FOR SIP: WITHOUT
OUTBOUND,YOU’RE A NO GO
Managing client certs is a
pain and a high cost.
The standards doesn’t
work, only outbound…

17. WORKTO DO
Kill SIPS:
Finally. Get rid of it.
Clarify SIP/TLS usage.
Mandate outbound for UAs.
Standardize SIP client
certificates.
Standardise DANE usage in
SIP.
Work on Peer-to-
peer security for all
protocols.