AN AUTHENTICATION AND DIGITAL SIGNATURE SCHEME BASED ON BLOCK CIPHER HASHING AND RSA CRYPTOGRAPHY

摘要

This paper introduces a scheme for authentication and digital signature. This scheme is based on block cipher hashing and RSA crypto-systems. At the sending end the message is encrypted, hashed, and signed and at the receiving end it is decrypted and verified. The implementation at both sides starts by computing public and private keys of the RSA crypto-system for the sender and receiver. The block cipher keys are obtained from a key string that is read from a file or given by the keyboard. Then, an initial hash sequence (H_0) is computed from two public number (Ns_0) and (gs_0) published by the sender. This sequence is used in conjunction with a block cipher technique to hash message blocks (M_i) with different lengths to obtain their encryption and hash values (C_i,S_i) respectively. The hash sequence is obtained according to the block length. It is updated from a block to the next. This is done by computing the value rr_i =(S_n~*r_i) mod n_s where (S_n) is the block hash and (r_i) is chosen from the values (l,α,β,γ) based on the concepts of quadratic residues where (α,β,γ) are published by the sender and satisfy certain conditions. The value (rr_i) is encrypted by the private key of the sender (d_s) and public key of the receiver (e_r) according to the RSA principles such that the cipher (RR_i) is obtained and sent along with the message code. The transmitted code of a block (M_i) is {C_i,RR_i,N_i,gs_i}.