Research On The Subliminal Channel In Digital Signature

The subliminal channel is a covert communication channel that constructed in the digital signature which based on the public key cryptography. In the subliminal channel, any subliminal message cannot be discovered except the authorized receiver.It is a typical modern information hiding technology and has many practical applications. In this dissertation, the background and the corresponding theories of the subliminal channel are introduced. We analyzed the character of the subliminal channel for the Digital Signature Algorithm (DSA), and also introduced the Newton Channel. The existence of the subliminal channel for the Elliptic Curve Digital Signatures Algorithm (ECDSA) was pointed out in this thesis. The channels based on DSA or ECDSA have a same disadvantage that the transmitter must send his private signature key to the subliminal receiver, which allows the subliminal receiver to forge the transmitter's signature in the broadband subliminal channel. For overcoming this disadvantage, a new subliminal channel was embeded in the ESIGN digital signature algorithm, in which there has not common secret key between the sender and the authorized subliminal receiver. Hence, the subliminal receiver cannot forge the transmitter's signature. The subliminal-free is also studied in this dissertation, and some schemes for the subliminal-free are carefully discussed. The scheme in which the warden attends the generation of the signature achieves the aim completely and insures the signer's authority. The main contributions in this thesis are as follows: 1) Based on the formal definition of digital signature and the Digital Signature Algorithm(DSA) , the existence mechanism of subliminal channel and some subliminal channels in the DSA are analyzed in detail. 2) The existence of the narrow-band and the broad-band subliminal channels in the Elliptic Curve Digital Signature Algorithm (ECDSA) is pointed out in this dissertation. And the characters of the subliminal in ECDSA are as same as that in the DSA.