Subject: [Sip] SIP authentication problem?

From: "Rami Lehtonen" <[email-masked]>
Date: Fri, 17 Aug 2001 14:27:27 +0300

Hello,

Does this following behaviour (to encrypt before authenticating) of SIP open
up some security holes, because now you can send the encrypted body with
valid signature even if you are not the original creator of that content?

   "Note that if a message is encrypted and authenticated using a digital
   signature, when the message is generated encryption is performed
   before the digital signature is generated. On receipt, the digital
   signature is checked before decryption."

Have you thought about this situation?

Regards, Rami Lehtonen

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From: James Undery <[email-masked]>
Date: Fri, 17 Aug 2001 12:32:40 +0100

> valid signature even if you are not the original creator of that content?

Sorry I don't quite follow why this is a problem, people often sign things they
didn't create, if you don't trust it don't sign it.

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From: "Rami Lehtonen" <[email-masked]>
Date: Fri, 17 Aug 2001 15:03:03 +0300

> didn't create, if you don't trust it don't sign it.

That might be the problem, because now we don't know who actually created
the content. It might be a problem also in case where the body contains some
sensitive information like the following example:

If there is e.g. a pre-paid ticket for some service in the body part, C
could capture that message sent originally by A, remove the signature and
include C's own signature and then send the message to B. Now B thinks that
C originally paid money for the service, because there is C's signature and
the content is encrypted using the B's public key as it should be.

Anyway this was just a thought. I was just curious to hear if somebody has
considered this as an authentication problem or not.