In data communications, digital signature schemes have been used to ensure non-repudiation of sending data and the integrality of data, and non-repudiation of receiving data is also very important in the secure communication. In the past years, this kind of cryptographic protocols was mainly implemented by the intervention of the trusted third party in transmission and encryption of data, thus the dependability and security of the trusted third party was a bottleneck in these secure systems. To solve this problem, an undeniable cryptographic protocol for both sender and receiver is proposed. It is more efficient. Finally, its applications in electric mail are discussed.