ABSTRACT

Multi signature is a signature scheme in which signers jointly generate a signature on a message. Threshold multisignature combines the traits of threshold signature and multisignature. In threshold multisignature, a group of users jointly generate a valid multisignature on a message and any one can verify the validity of the multisignature. However, in some applications the signed message is sensitive to the signature receiver. Directed signature scheme allows only a designated verifier to check the validity of the signature issued to him; and at the time of trouble or if necessary, any third party can verify the signature with the help of the signer or the designated verifier as well. Due to its merits, directed signature scheme is widely used in situations where the receiver’s privacy should be protected. By combining all these ideas, in this paper, we propose an ID-based Directed Threshold Multisignature Scheme from bilinear pairings. To the best of our knowledge this is the first directed threshold mulitsignature scheme in the ID-based setting from bilinear pairings. The security of the proposed scheme is based on the Computational Difie-Hellman Problem. Also we have discussed the security properties of the proposed scheme namely, robustness and unforgeability.