ElGamal signature values?

Michael Young mwy-opgp97@the-youngs.org
Sat Aug 11 19:15:02 2001


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From: "Jon Callas" <jon@callas.org>

> Can someone who is an implementer answer this? What do I need to do to put
> in the next draft? I'm going to put out another draft in the next couple of
> days -- there's time here at HAL -- and if I can clarify, I will.
I haven't implemented it yet, but I've asked a few times, and for lack of an answer, I've looked over the GnuPG code. GnuPG computes: a=g^k mod p); and, b=(h-a*x)/k mod (p-1)) where k is random and h is the (padded) message hash. It seems to apply the same PKCS padding as for RSA signatures. The two MPIs are encoded in that order (a,b). The computation matches that found in the Handbook of Applied Cryptography, among others. I can't comment on whether the PKCS padding is the usual treatment for ElGamal signatures, though. -----BEGIN PGP SIGNATURE----- Version: PGP Personal Privacy 6.5.3 iQEVAwUBO3Vm6WNDnIII+QUHAQEUMwgArXuSzEwh/5JrUyfb824IvMwW1nT6nj0X +RWMVWhDhij63kT95qo0yf/zNgSJ0qIuz0SSCwsTq2R8C6wknL//iIIU4IWDbNrf S1q6128GA9blwyJ4bWdfxnFABUSpPiUl7g5A+LBWPe5o1Q2wSAYKBLDiVJtL9AHG Db3R3++gnUo4ligmGCbzcU0dNepn0BEmAWAXmR3zH8xC2mNOPtIWBjm2JIUojZzX 99cB4hLjhw06I8H563eCo9avmc/2CTti+R9RNFWbu/CnKfSDL+++KhsgbkKIv7+M NdzpdJoKM6EmwPVbt8f9ZEZBRyMzotw9my9YiqVQaeybX4ZJFQ9O7g== =5/KR -----END PGP SIGNATURE-----