关键词: 保留格式加密, 数字型, 不同代数群, S盒, 弹性长度分组

Abstract: We study FPE (formatpreserving encryption) and propose a new numerical formatpreserving encryption algorithm, which significantly improves the performance of the formatpreserving encryption algorithm by not using CycleWalking. The block length is determined by decimal number of plaintext digits, including even and odd lengths. The core is to realize confusion and diffusion by constructing additive groups, finite fields, and Sbox, and use permutation algorithm and skipping algorithm to realize the preservation of the format. The key expansion algorithm outputs the block length of the plaintext flexibly and uses the key generator of the stream cipher to generate subkeys. A specific example is used to verify that the proposed algorithm can correctly implement formatpreserving encryption, and different algebraic group operations and nonlinear transformation of Sbox increase the security of the algorithm. Security analysis illustrates that the algorithm can meet the actual security requirements. Finally, compared with the FPE algorithm standard, FFX, which is proposed by NIST, the result shows that the proposed algorithm is about 30 times faster than FFX for a 128b block (32 decimal digits) of FFX.

Key words: formatpreserving encryption, numeric type, different algebraic group, Sbox, flexible block length