From: ljo@ausys.se (Johansson Lars)
Does anyone know whether David Chaum's patent on blind digital signatures extends to this application?
I don't think it would. Chaum's blinding protocol has one major difference: the blinding factor is applied by a different person than the one doing the signing. The purpose of the blinding is different, too; in Chaum's case the idea is to end up with a signature which is unknown to the signer, while with Kocher's "defensive blinding" the signature (or decryption) is an ordinary RSA one, and the blinding is just done internally by the signer to randomize the timing. (I gather BTW that the idea of the blinding is for the server to have pre-chosen a random r and pre-calculated r^d mod n, and then when he is given c to decrypt he first does c*r mod n and then decrypts this, then takes the result and divides by r^d.) It's conceivable that Kocher's blinding would be a patentable technique in itself, and not impossible that he has already applied for a patent before publishing. Probably he would have said so if that were his intention, though. Hal "Blind defensively - watch out for the other guy..."