## Abstract

For many proofs of knowledge it is important that only *the verifier designated by the confirmer* can obtain any conviction of the cor- rectness of the proof. A good example of such a situation is for undeniable signatures, where the confirmer of a signature wants to make sure that only the intended verifier(s) in fact can be convinced about the validity or invalidity of the signature.

Generally, authentication of messages and off-the-record messages are in conflict with each other. We show how, using designation of verifiers, these notions can be combined, allowing authenticated but privat con- versations to take place. Our solution guarantees that *only* the specified verifier can be convinced by the proof, even if he shares all his secret information with entities that want to get convinced.

Our solution is based on *trap-door commitments* [4], allowing the desig- nated verifier to open up commitments in any way he wants. We demon- strate how a trap-door commitment scheme can be used to construct designated verifier proofs, both interactive and non-interactive. We ex- amplify the verifier designation method for the confirmation protocol for undeniable signatures.

### Keywords

- Commitment Scheme
- Logical Entity
- Computational Entity
- Undeniable Signature
- Zero Knowledge Proof

*These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.*

Research supported by NSF YI Award CCR-92-570979, Sloan Research Fellowship BR-3311, and The Royal Swedish Academy of Sciences.

Research supported by NSF YI Award CCR-92-570979 and Sloan Research Fellowship BR-3311.

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Jakobsson, M., Sako, K., Impagliazzo, R. (1996). Designated Verifier Proofs and Their Applications. In: Maurer, U. (eds) Advances in Cryptology — EUROCRYPT ’96. EUROCRYPT 1996. Lecture Notes in Computer Science, vol 1070. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-68339-9_13

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