> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, February 28, 2001 12:30 PM
> To: Arunachalam Venkatraman; [EMAIL PROTECTED]
> Subject: RE: [Sip-implementors] CANCEL with Authorization
>
>
>
>
>
> Ok, its like this :
>
> UA1 sends a INVITE to UA2 and this comes back to UA1 for authorization
> (401).
> Meanwhile another UA (UA3 say) sends a spurious CANCEL (with matching
> Call-ID, etc)
> to UA2 with an aim to CANCEL the call between UA1 and UA2.
> This is where authorization for CANCEL is needed.....
>
> Regards,
> Subhash.
>
>
This has been discussed before. The end to end authorization mechanisms
don't work for CANCEL, since CANCEL can be generated by any intermediate
entity on the sip proxy path. Fundamentally, CANCEL is a hop by hop
operation.
Therefore, securing it requires hop by hop security mechanisms. The solution
is that proxies have a security association between them (TLS or IPSec). If
a proxy accepts an INVITE over one of these connections, it accepts a CANCEL
for that transaction only over that same connection. This eliminates all
these attacks whereby malicious third parties attempt to cancel my calls by
injecting cancels into the proxy path.
-Jonathan R.
---
Jonathan D. Rosenberg 72 Eagle Rock Ave.
Chief Scientist First Floor
dynamicsoft East Hanover, NJ 07936
[EMAIL PROTECTED] FAX: (973) 952-5050
http://www.cs.columbia.edu/~jdrosen PHONE: (973) 952-5000
http://www.dynamicsoft.com
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