Undeniable signature

Undeniable signatures are a form of digital signature invented by David Chaum and Hans van Antwerpen in 1989. They have two distinctive features,

1. The verification process is interactive, so that the signatory can limit who can verify the signature.
2. A disavowal protocol, which is a cryptographic protocol that allows them to determine whether a given signature is a forgery.

The first means that a signatory can allow only others who are authorized to access the document to verify their signature. If the document were to be leaked to a third party, the third party would be unable to verify that the signature is genuine. This is a designated verifier signature.

However, because of this property it means that the signatory may deny a signature which was valid. To prevent this, there is the second property, a method to prove that a given signature is a forgery.

See also

• Topics in cryptography

References

• David Chaum, Hans van Antwerpen: Undeniable Signatures; Crypto'89, LNCS 435, Springer-Verlag, Berlin 1990, 212-216.