Abstract:

Due to the property that the 3-round Advanced Encryption Standard（AES） ciphertexts have a polyno-mial expression with a low degree of less than 255,a method of interpolation attack on the round-reduced AES is presented,that is,through the Lagrange interpolation formula,the polynomial with 254 degrees can be obtained using 255 values.The algebraic representation of the AES on its plaintexts and ciphertexts is then studied,and the relevant results and the corresponding proofs are also given.According to the proposed attack method,the key of 4-round AES cipher is found using only 2^8 chosen plaintexts,and the key of 5-round AES cipher is successfully broken using 2^11 chosen plaintexts.Moreover,this attack method can be extended to the 6-round AES cipher.

Key words: cryptography, block cipher, interpolation attack, Advanced Encryption Standard