Time Capsule Signature, first formalized by Dodis and Yum in Financial Cryptography 2005, is a digital signature scheme which allows a signature to bear a (future) time t so that the signature will only be valid at time t or later, when a trusted third party called time server releases time-dependent information for checking the validity of a time capsule signature. Also, the actual signer of a...

Blindness and unforgeability are two essential security requirements of a secure blind signature scheme. Blindness means that after interacting with various users, the signer can never be able to link a valid message pair. Blindness is meaningless if after interacting with various users, the signer is able to link a valid message signature pair. This security vulnerability is known as linkabili...

This paper will show that Hsu and Wu’s efficient nonrepudiable threshold proxy signature scheme with known signers and Yang, Tzeng and Hwang’s efficient nonrepudiable threshold proxy signature scheme with known signers are insecure. The malicious original signer can forge a valid threshold proxy signature for any message and any warrant after getting a valid proxy signature. In addition, since ...

In 2004, Yang et al. proposed an efficient (t, n) threshold proxy signature scheme with known signers. However, Maimani et al. showed that a malicious original signer can forge a valid proxy signature for any message in Yang et al.’s scheme and further proposed an improvement to remedy such an attack. In this paper, we will show that in Maimani et al.s improvement, a malicious original or proxy...

Allowing a proxy signer to generate a signature on behalf of an original signer, a proxy signature should satisfy the property of strong unforgeability: anyone except the designated proxy signer cannot create a valid proxy signature on behalf of the original signer. Since proxy signatures, as well as their derivatives, can be used in many applications in reality, such as secure mobile agent, e-...