A randomized protocol for signing contracts
Communications of the ACM
A digital signature scheme secure against adaptive chosen-message attacks
SIAM Journal on Computing - Special issue on cryptography
Optimistic protocols for fair exchange
Proceedings of the 4th ACM conference on Computer and communications security
Efficient verifiable encryption (and fair exchange) of digital signatures
CCS '99 Proceedings of the 6th ACM conference on Computer and communications security
Securely combining public-key cryptosystems
CCS '01 Proceedings of the 8th ACM conference on Computer and Communications Security
Abuse-Free Optimistic Contract Signing
CRYPTO '99 Proceedings of the 19th Annual International Cryptology Conference on Advances in Cryptology
Efficient Fair Exchange with Verifiable Confirmation of Signatures
ASIACRYPT '98 Proceedings of the International Conference on the Theory and Applications of Cryptology and Information Security: Advances in Cryptology
Off-Line Fair Payment Protocols Using Convertible Signatures
ASIACRYPT '98 Proceedings of the International Conference on the Theory and Applications of Cryptology and Information Security: Advances in Cryptology
ASIACRYPT '01 Proceedings of the 7th International Conference on the Theory and Application of Cryptology and Information Security: Advances in Cryptology
1-out-of-n Signatures from a Variety of Keys
ASIACRYPT '02 Proceedings of the 8th International Conference on the Theory and Application of Cryptology and Information Security: Advances in Cryptology
Designated verifier signature schemes: attacks, new security notions and a new construction
ICALP'05 Proceedings of the 32nd international conference on Automata, Languages and Programming
Generic construction of (identity-based) perfect concurrent signatures
ICICS'05 Proceedings of the 7th international conference on Information and Communications Security
Optimistic fair exchange of digital signatures
IEEE Journal on Selected Areas in Communications
Efficient and secure protocol in fair document exchange
Computer Standards & Interfaces
Contract signature in e-commerce
Computers and Electrical Engineering
Concurrent signatures with fully negotiable binding control
ProvSec'11 Proceedings of the 5th international conference on Provable security
A fair concurrent signature scheme based on identity
HPCA'09 Proceedings of the Second international conference on High Performance Computing and Applications
Trusted firmware services based on TPM
INTRUST'09 Proceedings of the First international conference on Trusted Systems
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In Eurocrypt 2004, Chen, Kudla and Paterson introduced the concept of concurrent signatures, which allow two parties to produce two ambiguous signatures until the initial signer releases an extra piece of information (called keystone). Once the keystone is publicly known, both signatures are bound to their true signers concurrently. In ICICS 2004, Susilo, Mu and Zhang further proposed perfect concurrent signatures to strengthen the ambiguity of concurrent signatures. That is, even if the both signers are known having issued one of the two ambiguous signatures, any third party is still unable to deduce who signed which signature, different from Chen et al.'s scheme. In this paper, we point out that Susilo et al.'s two perfect concurrent signature schemes are actually not concurrent signatures. Specifically, we identify an attack that enables the initial signer to release a carefully prepared keystone that binds the matching signer's signature, but not the initial signer's. Therefore, their schemes are unfair for the matching signer. Moreover, we present an effective way to avoid this attack so that the improved schemes are truly perfect concurrent signatures.