Abstract: Subliminal channels in EDL signature were constructed firstly, then an interactive subliminal-free protocol was designed. It is shown that the proposed protocol can completely close subliminal channels existing in the random pa- rameters in EDL signature. hhe proposed protocol is proved to be secure in RO(random oracle) model assuming the CDH(computational Diffie-hellman) problem is hard. In the new protocol, the warden participates the generation of sig- nature, but can not sign messages. Thus, the signature authority of the signer is guaranteed. To generate a signature, it only needs to perform 2 and 3 modular exponentiation for the signer and the warden respectively.

Key words: Cryptography,Digital signature,Information hiding,Subliminal channel,Free protocol,Random oracle model