International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Security of Verifiably Encrypted Signatures

Markus Rückert
Dominique Schröder
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Abstract: In a verifiably encrypted signature scheme, signers encrypt their signature under the public key of a trusted third party and prove that they did so correctly. The security properties are unforgeability and opacity. Unforgeability states that a malicious signer should not be able to forge verifiably encrypted signatures and opacity prevents extraction from an encrypted signature. This paper proposes two novel fundamental requirements for verifiably encrypted signatures, called \emph{extractability} and \emph{abuse-freeness}, and analyze its effects on the security model of Boneh et al. Extractability ensures that the trusted third party is always able to extract a valid signature from a valid verifiably encrypted signature and abuse-freeness guarantees that a malicious signer, who cooperates with the trusted party, is not able to forge a verifiably encrypted signature. We further show that both properties are not covered by the model of Boneh et al., introduced at Eurocrypt 2003.
  title={Security of Verifiably Encrypted Signatures},
  booktitle={IACR Eprint archive},
  keywords={public-key cryptography / Verifiably encrypted signatures, Online contract signing, Security Model},
  note={ 14297 received 12 Jan 2009, last revised 22 Feb 2009},
  author={Markus Rückert and Dominique Schröder},