[Nym3-devel] SIG size for control messages sent to the nymserver.

[Nick Mathewson]

On Sun, Apr 10, 2005 at 01:52:28PM +0200, Laurent Fousse wrote:
> Hi,
> 
> nym-specs say every control message sent to the nymserver carries a
> RSA-OAEP signature of SHA1(remainder_of_message), section 4.3
> 
> It also says the SIG size is PK_LEN = 256, however in the NEWPK specs
> (section 4.3.4) the size of the identity key used for this signature
> may be 128 or 256 octets, leading to a signature size of 128 or 256
> octets.
> 
> What do you suggest?
> 
>  (1) force the key size to 2048 bits,
>  (2) zero-pad the 128 octets signature to get a 256 octets signature,
>  (3) add one leading octet that gives the signature length.
> 
> I'm not really in favour of (3), and the key generation time might
> bother users of slow machines for a forced 2048 bits keysize.

I'd favor (1) myself as the easiest option; 1024-bit keys just seem
too small these days.  But another option is to put the SIG part of
the message header _after_ the NL and NYM fields, so the server knows
which key to use and how long it is.  We don't need to worry about
those fields being unsigned---if they are altered, the signature won't
be correct unless the signature is altered too, which is impossible
without the correct private key.

How does that sound?

-- 
Nick Mathewson
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