Efficient signature schemes based on polynomial equations
Proceedings of CRYPTO 84 on Advances in cryptology
An efficient signature scheme based on quadratic equations
STOC '84 Proceedings of the sixteenth annual ACM symposium on Theory of computing
Zero-knowledge proofs of identity and veracity of transaction receipts
Lecture Notes in Computer Science on Advances in Cryptology-EUROCRYPT'88
Provably Unforgeable Signatures
CRYPTO '92 Proceedings of the 12th Annual International Cryptology Conference on Advances in Cryptology
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Recently Okamoto and Shiraishi proposed a public key authentication system [1]. The security of the scheme is based on the difficulty of solving quadratic inequalities. This new system is interesting since the amount of computing needed for the proposed scheme is significantly less than that needed for an RSA encryption.This report is an investigation into the security of the proposed digital signature scheme. We demonstrate that if the system is used as it is presented, an opponent could sign messages without factoring the modulus. Further, we suggest a modification which may not have the same flaw as the proposed scheme.