> -----Original Message-----
> From: Albee Vimal [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, April 11, 2001 2:19 AM
> To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: Encryption
> 
> 
> Hi
> 
> Supposing a Sip Message has some headers in the clear and 
> some encrypted and
> the decryption key to be used is known only after parsing the 
> clear headers.
> Eg.The gateway uses the To Sip header to identify the final 
> user and then
> picks a key  to decrypt
> 
> How does the UAS (Gateway in this example) get the key to 
> decrypt?

It would be the private key of the gateway. The gateway knows its own
private key.

 Does the
> gateway talk to a trusted third party to get the private key 
> of the user.

The gateway will need the public key of the user in order to encrypt the
response for the user. This key is carried in the SIP message for PGP.
However, as I have noted in other emails, PGP is being deprecated in favor
of S/MIME and PGP/MIME.

> 
> Is the message encrypted with the public key of the Gateway 
> (as suggested in
> the RFC). The question in that case is since the UAC does not know the
> Gateway that is going to be used apriori, What key will he use?

This is the problem of a public key infrastructure (PKI) which is a very
hard problem in general.

-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.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com
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