SIP authentication – Thoughts please

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We have a scenario where we need multiple discrete SIP trunks (peers)
from/to a single endpoint. Because the authentication system starts by
matching IP address, it only ever matches on one of the SIP peer
entries, and ignores the others. This is documented behaviour and as
such is “correct”. I would like to propose an extension to how SIP
peers are authenticated in this case:

1) Initial INVITE arrives, scan the list of all matching peer IP addresses.
If a peer with no password is found, proceed with that peer immediately.

2) …otherwise, a password is required, so send 407 challenge

3) INVITE arrives with Basic-Auth.
Scan for /all/ matching peers based on IP address. If one of the
matching peers has a section name matching the Basic-Auth username,
use it to proceed.

4) I am not sure whether it is worth dropping through and testing auth
against other peers if there is no username match. Can auth ever
succeed under those circumstances (password matches, but not

Thanks for any feedback.


2 thoughts on - SIP authentication – Thoughts please

  • Am 07.10.10 10:52, schrieb Steve Davies:


    i just want to say something about point 4 which comes to my mind about

    If you use UDP its very easy to fake the source ip of a call so do you
    really want to open a door to an attacker by authenticate only by ip and
    passwort which can match to any peer with the same ip adress? To
    bruteforce this would be much easier than to bruteforce against sending
    IP, right username and right password.

    Have you tried to use different ports to register? i think this could help.

    best regards


  • I was not clear. By option 4) I intended that you test the password
    against other peers with a matching IP address. I am not sure whether
    the username is included in the SIP password hash, so do not know
    whether there is even any point in doing so. As far as I can tell, in
    the EXISTING sip stack, digest username is not used to determine which
    peer to authenticate with, it just uses the first peer with a matching

    AFAIK, Asterisk will only operate on one port, and the remote end is a
    major ITSP who will not be wanting to listen to me making odd requests

    Thanks for the feedback!