Paper 2009/027

Security of Verifiably Encrypted Signatures

Markus Rückert and Dominique Schröder


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.

Available format(s)
Public-key cryptography
Publication info
Published elsewhere. Unknown where it was published
Verifiably encrypted signaturesOnline contract signingSecurity Model
Contact author(s)
schroeder @ me com
2009-02-22: revised
2009-01-14: received
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      author = {Markus Rückert and Dominique Schröder},
      title = {Security of Verifiably Encrypted Signatures},
      howpublished = {Cryptology ePrint Archive, Paper 2009/027},
      year = {2009},
      note = {\url{}},
      url = {}
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