To ensure the integrity of the data packets, and not be tampered with, can add message packet identification code. In the sending process will change the length of plaintext M is divided into 64-bit length group M1,M2,…Mn, then the group formed by XOR operation of a 64-bit string of N=M1 ⊕ M2 ⊕…Mn, then use the DES encryption algorithm on the N to
form a 64-bit identification information CK(M). Finally, M and CK(M) sent to the receiver.
In the receiving process, the receiver will receive the same algorithm to calculate the express M to identify and compare
their own calculated identification information is equal to the received identification information CK(M), so if the process of
message sending been tampered with or is counterfeit, you can discover packet identification process.