Protocols for simultaneous signing contracts

Signing electronic messages authentication is an issue of significant importance for computer and telecommunication systems. To solve efficiently some special practical problems the multisignature protocols are applied. New multisignature protocols based on the elliptic curves and discrete logarithm problem in finite groups are proposed to solve the problem of simultaneous signing contracts. The protocols provide simultaneous generation of the collective digital signature. There are considered the following two cases: 1) a group of signers are signing simultaneously one document and 2) several different groups of signers are signing several different documents. The signature verification is performed using collective public key computed from the whole set of individual public keys as the some convolution of this set.