Proxy signature schemes have been invented to delegate signing rights. The paper proposes a new concept of Identify Based Strong Bi-Designated Verifier threshold proxy signature (ID-SBDVTPS) schemes. Such scheme enables an original signer to delegate the signature authority to a group of ‘n’ proxy signers with the condition that ‘t’ or more proxy signers can cooperatively sign messages on behal...

Last Time: Simulation Sound NIZKS & Connection to CCA Security. Last time we introduced Simulation-Sound NIZKs, and constructed a 1-Time Simulation Sound NIZK (1-SS NIZK). We then showed how to get CCA secure encryption from CPA encryption and NIZKs in one of two ways: using standard NIZK and n copies of a CPA encryption scheme ([DDN00]) or using 1-SS NIZK and 2 copies of a CPA encryption schem...

Key-homomorphic properties of cryptographic objects have proven to be useful, both from a theoretical as well as a practical perspective. Important cryptographic objects such as pseudorandom functions or (public key) encryption have been studied previously with respect to key-homomorphisms. Interestingly, however, signature schemes have not been explicitly investigated in this context so far. W...

The concept of Designated Verifier Signatures (DVS) was introduced by Jakobsson, Sako and Impagliazzo at Eurocrypt’96. These signatures are intended to a specific verifier, who is the only one able to check their validity. In this context, we formalize the notion of privacy of signer’s identity which captures the strong designated verifier property investigated in their paper. We propose a vari...

Key-homomorphic properties of cryptographic objects have proven to be useful, both from a theoretical as well as a practical perspective. Important cryptographic objects such as pseudorandom functions or (public key) encryption have been studied previously with respect to key-homomorphisms. Interestingly, however, signature schemes have not been explicitly investigated in this context so far. W...

Undeniable signature schemes are not publicly verifiable. Therefore, in order to prove the validity/invalidity of a message-signature pair, the signer needs to provide a proof for the rightful verifier. Since the introduction of undeniable signature schemes, various proof systems with different properties and features have been introduced to be incorporated in the structure of such schemes. Amo...

A convertible authenticated encryption scheme allows a designated receiver to recover and verify a message simultaneously, during which the recipient can prove the dishonesty of the sender to any third party if the sender repudiates her signature later. In this paper, after showing some weaknesses in Wu et al.’s [21] and Huang et al ’s [10] convertible authenticated encryption schemes, we propo...

We introduce the notion of abuse-free distributed contract signing, that is, distributed contract signing in which no party ever can prove to a third party that he is capable of choosing whether to validate or invalidate the contract. Assume Alice and Bob are signing a contract. If the contract protocol they use is not abuse-free, then it is possible for one party, say Alice, at some point to c...

In this article, we shall adopt the concepts of elliptic curve cryptosystems and self-certified public keys to build a novel digital signature scheme with message recovery. The public key and the identity of the user can be authenticated simultaneously in recovering the message. In addition, we shall also present three extended digital signature schemes based on the proposed scheme. The first i...