Patent ID: 7877610

Claim:
A cryptographic unit for digitally signing a plaintext message exchanged between a pair of correspondents in a data transmission system, one of said pair of correspondents being the signer and having a private key a and a public key derived from the private key a, said public key being available to the other of said pair of correspondents, said cryptographic unit comprising a processor configured for: subdividing said plaintext message into a first plaintext bit string H and a second plaintext bit string V; computing a first signature component c as a function of said first plaintext bit string H wherein the plaintext bit string H is hidden in said signature component c; computing an intermediate signature component c′ as a function of said first signature component c and said second plaintext bit string V; computing a second signature component s as a function of said intermediate signature component c′ and said private key a; and forming a signature (s,c,V) containing said first signature component c, said second signature component s, and said second plaintext bit string V as discrete signature components; whereby during verification, said second plaintext bit string V is available from said signature (s,c,V) as an input to a verification protocol.