[VOIPSEC] SIP B2BUA and Digest Authentication using

[Simon Horne]

At 07:55 AM 6/11/2005, Christopher A. Martin wrote:
..deleted
>I responded earlier tonight before I had a chance to read this original 
>question...I have a few of my own, and my earlier answer also applies to 
>this response.
>
>First of all, do the sip server (SIP UAS) and the clients (SIP UA) support 
>server side/client side certificates (This is something that I am putting 
>some personal research into right now)?
>
>Much like a web server can authenticate based on the attributes of a 
>digital X.509 certificate as well as the clients can trust a ca 
>certificate, a form of trust should be able to exist between clients and 
>servers. Right now I am focusing on open source servers and soft clients 
>in my personal research, and see ways to augment servers/clients that lack 
>these capabilities by implementing STUNNEL with some obvious side effects 
>as well as benefits which of course reside within a trusted administrative 
>domain.

As you are aware Chris, the H.323 secure softphone we are developing does 
something similar to this (example in next beta release).

The provider can issue the client with a PKCS#12 password encrypted file 
(via email) which contains a X.509 Cert, Private key and CA Chain. These 
are loaded into the softphone at startup. The softphone will automatically 
authenticate the X.509 cert against its loaded CA Chain and once 
authenticated will use the DN (distinguished Name) of the X.509 as its 
username (or user id) to attempt to gain admission to the specified 
gatekeeper using MD5 or HMAC-96 hash.
The gatekeeper can then use Radius to authenticate the admission request. 
(Many commercial GK's already support radius including the open source 
gnugk project using freeradius)

The great advantage of using X.509 is that you can insert a signed cert 
(using EP1's private key) into EP1's call setup message carried end-to-end 
to use as an authentication mechanism. If the CA that signed EP1's cert is 
present in EP2's CA chain then the caller can be verified and 
authenticated. EP2 can then decide it's own security policy and reject the 
call if the cert is missing or invalid.

Simon



Simon Horne
Director
Packetizer Labs
www.packetizer.com/labs