[curves] Unifying public key formats

Trevor Perrin trevp at trevp.net
Wed Jan 21 12:56:56 PST 2015

On Wed, Jan 21, 2015 at 10:29 AM, Trevor Perrin <trevp at trevp.net> wrote:
> D) DH-type keys everywhere
> All public keys omit the sign bit (Montgomery x public keys are used
> for everything).  For signatures, the sign bit is included as part of
> the signature (Robert Ransom suggested this, and TextSecure is using
> it).  This means a very slight reduction in security, as each party
> essentially has two signature keys, rather than one, so an attacker
> could try to forge a signature against either of these keys.

Another way to do this - instead of "Ransom's trick" there's "Jivsov's
trick" where the private key is adjusted - if necessary - to always
make the sign bit 0:



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