Research on the Parallel SM4-OFB Acceleration Based on Multiple Rounds of Iteration

In OFB mode, the output of the cryptographic algorithm is fed back to the input of the cryptographic algorithm. The OFB mode does not directly encrypt plaintext through cryptographic algorithms, but generates ciphertext blocks by XOR combining plaintext blocks with the output of cryptographic algorithms. In OFB encryption mode, messages are treated as bitstreams, and the output of block encryption is added to the encrypted messages, making it difficult for bit errors to propagate. The SM4 algorithm is a symmetric cryptographic technique developed by the Chinese National Cryptographic Administration and standardized as part of the State Encryption Standard in China. SM4 is widely adopted in various applications, including wireless communication systems and secure data transmissions. In this paper, a fast implementation method of SM4 in OFB mode is proposed. We calculate the possible parallelization operations in OFB mode using the operational relationship between the SM4 algorithm round functions, and ensure the correctness of SM4-OFB encryption through a feedback compensation method.