Abstract: Cryptographic methods are disclosed, which allow a prover party, who holds a number of secrets, to demonstrate satisfiable formulas of propositional logic, wherein the atomic propositions are linear relations between the secrets. The demonstration reveals no more information than is contained in the formula itself. Some implementations allow an unlimited number of such demonstrations to be made, without revealing any additional information about the secrets, whereas other implementations ensure that the secrets, or some of the secrets, will be revealed, if a demonstration is performed more than a predetermined number of times. The demonstrations may be zero-knowledge proofs, or signed proofs.

Abstract: A method for an issuer party to issue DSA-like secret-key certificates that can be blinded only restrictively. The method includes the step of generating a secret key (x.sub.0,y) and a public key (descr(G.sub.q), g, h.sub.0, g.sub.1, descr((.cndot.))), wherein q is a prime number, Gq is a group of order q, in which computing discrete logarithms is substantially infeasible, but in which multiplication, determination of equivalence of elements and generation of substantially random numbers is relatively easy, descr(G.sub.q) is a description of G.sub.q including q, descr((.cndot.)) is the description of a hash-function (.cndot.) for which computing inverses is substantially infeasible, x.sub.0, and y are elements of the ring, of integers modulo q, g is an element of order q in the group, G.sub.q, h.sub.o is equal to g.sup.x.sbsp.0 ; and g.sub.1 is equal to g.sup.y. The method further includes the step of issuing to a receiver party a secret-key certificate (r,a) in on a public key h in G.sub.

Abstract: A cryptographic method is disclosed that enables the issuer in a secret-key certificate issuing protocol to issue triples consisting of a secret key, a corresponding public key, and a secret-key certificate of the issuer on the public key, in such a way that receiving parties can blind the public key and the certificate, but cannot blind a predetermined non-trivial predicate of the secret key even when executions of the issuing protocol are performed in parallel.

Abstract: Cryptographic methods and apparatus are disclosed that enable forming and issuing of secret-key certificates. Contrary to the well-known cryptographic technique of public-key certificates, where a public-key certificate is a digital signature of a certification authority on a public key, pairs consisting of a public key and a corresponding secret-key certificate can be generated by anyone. As a result, a public-key directory based on secret-key certificates cannot help anyone in attacking the signature scheme of the certification authority, and it does not reveal which of the listed public keys have been certified by the certification authority and which have not.Yet, if a party associated with a public key can perform cryptographic actions with the secret key corresponding to its public key, such as decrypting, digital signing, issuing a secret-key certificate, and identification, then the certificate must have been computed by the certification authority.

Abstract: Cryptographic apparatus and means are disclosed for each of three types of participants in an electronic system for privacy-protected transfer of certified information. This invention reveals protocols that improve efficiency and security in such systems, and allows a variety of useful extensions in functionality without difficulty. This is achieved by a restrictive blind signature protocol in combination with a testing protocol. The restrictive blind signature protocol allows the certifying party to encode data into certified information that it provides to a receiving party, such that it cannot be altered or modified by the receiving party. The testing protocol enables parties to prove a variety of characteristics about the encoded data in their certified information.

Abstract: Cryptographic apparatus and means are disclosed for each of three types of participants in an electronic system for privacy-protected transfer of certified information. This invention reveals protocols that improve efficiency and security in such systems, and allows a variety of useful extensions in functionality without difficulty. This is achieved by a restrictive blind signature protocol in combination with a testing protocol. The restrictive blind signature protocol allows the certifying party to encode data into certified information that it provides to a receiving party, such that it cannot be altered or modified by the receiving party. The testing protocol enables parties to prove a variety of characteristics about the encoded data in their certified information.