[noise] MAC'ing recipient public key

[Stephen Touset]

On Jul 13, 2014, at 10:08 PM, Trevor Perrin <trevp at trevp.net> wrote:

> Another change:
> 
> The recipient pubkey is included in the additional authenticated data
> for both box MACs.  This ensures that if the sender can decrypt a box,
> it must have been encrypted to the sender's pubkey.  While this can
> also be accomplished by taking care with the ECDH, I think it's
> simpler to just include the recipient's key into the mac.

Perhaps I’m overlooking something, but this seems impossible to reconcile with pipes.

When a server first sees a client, the only thing they receive is the client’s ephemeral key. They have no forehand knowledge of the client’s long-term public key, and thus cannot properly compute the MAC.

-- 
Stephen Touset
stephen at squareup.com