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Security Analysis of the Pomykała-Barabasz Scheme

Li F., Hu Y.

Fundamenta Informaticae

2007

Vol. 80, nr 4

453-459

In 2006, Pomykala and Barabasz [Fundamenta Informaticae 69 (2006) 411–425] proposed an elliptic curve based threshold proxy signature scheme which requires shorter cryptographic keys.They claimed that their scheme satisfies the secrecy, the proxy protected, the unforgeability, the non-repudiation, and the known signers. However, in this paper, we show that their scheme cannot achieve the proxy protected, the unforgeability and the non-repudiation by demonstrating a conspiracy attack. In this attack, any t malicious proxy signers can collusively impersonate some other proxy signers to generate proxy signatures.

An Efficient and Practical (t, n) Threshold Proxy Signature Scheme with Known Signers

Huang H-F., Chang C-C.

Fundamenta Informaticae

2003

Vol. 56, nr 3

243-253

Previously, all of the proposed threshold proxy signature schemes which have been based on the discrete logarithms required a protocol to generate and verify a shared secret among the proxy group. Therefore, it is necessary for the proxy signers to execute a lot of expensive modular exponential computations and communications to obtain and verify a shared secret. Thus, it is very time-consuming to construct the proxy signature. Moreover, some of the existing threshold proxy signature schemes reveal that the receiver cannot find out who signed the proxy signatures. In this paper, we proposed a practical, efficient, and low communications (t, n) threshold proxy signature scheme based on RSA cryptosystem. By using our way, not only the original signer can know who generated the proxy signature, but also everyone can be a verifier to certify the actuality of the group signers who made it. So, it is very convenient to clarify the responsibility of the document's signers fairly.