Multi-signature with anonymous threshold subliminal channel for ad-hoc environments

The multi-signature is a special signature which is generated by multiple group members with the knowledge of multiple private keys, while the subliminal channel is a covert communication channel that can be used to send a secret message to an authorized receiver but the message cannot be discovered by any unauthorized receiver. A (t,n) threshold scheme allows a secret to be shared among n users so that only t or more users can cooperatively reconstruct the secret. All multi-signature schemes available are for either discrete-logarithm-type (DL-type) keys only or RSA-type keys only. In this paper, we propose a multi-signature scheme, which allows mixture use of DL and RSA-type keys and is suitable for the ad-hoc environments. Then based on the proposed multi-signature scheme, we propose a anonymous threshold subliminal channel scheme, in which the subliminal message sender is indistinguishable and the subliminal message cannot be derived without the cooperation oft or more users in the group, where t is a threshold value.