Patent ID: 6697488
Filing Date: 2004-02-24
Classification: H04L

Abstract:
A method for generating a cryptographic key, comprising the steps of:choosing at least a first, second, and third exponent-number (x1, x2, z) as part of a private key, from a set Zq of elements modulo q, whereby q is preferably a large prime, (a.) choosing at least a first base-group-number (g1) and a second base-group-number (g2) from a cryptographic group (G), (b.) deriving from the chosen numbers (g1, g2, x1, x2, z) at least a first and second group-number (c, h), said first group-number (c) being derivable from the product of said first base-group-number (g1) raised to the power of a first monotone function Æ’1 of said first exponent-number (x1) and said second base-group-number (g2) raised to the power of a second monotone function Æ’2 of said second exponent-number (x2), said second group-number (h) being derivable from at least one of said base-group-numbers (g1, g2) raised to the power of a third monotone function Æ’3 of said third exponent-number (z), (c.) making the chosen at least two base-group-numbers (g1, g2) and said derived at least two group-numbers (c, h) part of a public key as public-key numbers (g1, g2, c, h), such that said public-key numbers (g1, g2, c, h) are usable as bases and at least a chosen single exponent-number (r) is usable as exponent together with a plaintext (m) for forming a ciphertext (t), comprising at least a first universal and second universal cipher-number (u1, u2) and an encryption cipher-number (e), applying the ElGamal scheme, said ciphertext (t) further comprising a verification cipher-number (v) with which said ciphertext (t) is verifiable, said ciphertext (t) being decryptable according to said ElGamal.