Improving Data Integrity in Communication Systems by Designing a New Security Hash Algorithm

The objective of this paper is to design a new secure hash algorithm with final hash code length 512 bits. The proposed hash code algorithm based on the combination of SHA-256 algorithm -with modification in its message expansion- and MD5algorithm based on double-Davis-Mayer scheme to reduce the weakness existing in these functions.In this paper; we modified message expansion for SHA-256 in the proposed algorithm .By using MATLAB, The proposed algorithm has been simulated. And hash code for different messages is obtained using MD5, SHA-256, combination of MD5 and SHA-256 with final hash code length 265 bits algorithms and the proposed algorithm . Hash code of the proposed algorithm is different from hash code obtained by MD5, SHA-256 and combination of MD5 and SHA-256 with final hash code length 256 bits algorithms for the same messages. Avalanche test, with one bit difference and more than one bit difference, is applied toSHA-256, combination of MD5 and SHA-256 with final hash code length 256 bits and the proposed algorithm .The proposed algorithm passed avalanche test with higher probability than SHA-256   and combination of MD5 and SHA-256 with final hash code length 256 bit algorithms .The proposed algorithm is more complicated and more secure