Abstract: According to the research status of Cache Side-Channel attacks,on machines equipped with Intel i5-4590 four-core,3.3GHz CPU processor,flush +flush timing attack is carried out on AES fast encryption method(AESFastEngine.Java) of Bouncy Castle JDK1.0 library in Linux system virtual environment.When the encryption process continues to execute,flush+flush method is used to traverse the shared main memory address to detect the active address set (s-box address),and then the S-box offsets is found to monitor table entries in the s-box offset.Select ciphertext value corresponding to shorter flush+flush time from all ciphertexts,and restore the last round key value with the table entry value of S box,that is,the key value used in the last round can be restored by determining the usage of entries in S-box.This method needs a large number of known ciphertext,and can accurately calculate the offsets of S-box and the last round key values.

Key words: AES table look-up method, Cache timing attack, flush＋flush attack, RiJndael algorithm, S-box offsets