dh question

Paul Crowley paul at ciphergoth.org
Tue Jun 7 15:51:36 PDT 2005

Brad Fitzpatrick wrote:
> When I run H() on gx^y mod p, what are the actual bytes I'm running H()
> on?

As far as cryptographic security goes, any of those are fine, so long as 
different integers always result in different inputs to H.  My 
preference for the map from integers to bytes is two's complement MSB, 
which Java uses and understands.  Since all our integers are positive, 
that just means adding a 0 byte at the start if the high bit is set.

This map comes up twice, once for the hash function and once for the 
integer transit encoding (followed by Base64).
\/ o\ Paul Crowley, paul at ciphergoth.org
/\__/ http://www.ciphergoth.org/

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