Patent ID: 7583800

Claim:
An encryption method for dividing a first plaintext bit stream of length 2 n into first and second sub-bit streams of length n, dividing a second plaintext bit stream of length 2 n into third and fourth sub-bit streams of length n, and generating a ciphertext bit stream of length 2 n from the first, second, third and fourth sub-bit streams using 2-rounds of encryption, the method comprising the steps of: performing the first-round of encryption by encrypting the received the first and second sub-bit streams with predetermined first encryption codes an odd number of times and outputting first and second ciphertext bit streams, wherein the first ciphertext bit stream is encrypted a first number of times and the second ciphertext bit stream is encrypted a second number of times, the second number of times exceeding the first number of times; generating a first operated ciphertext bit stream by performing a logical exclusive-OR-operation on the first ciphertext bit stream and the third sub-bit stream; generating a second operated ciphertext bit stream by performing a logical exclusive-OR operation on the second ciphertext bit stream and the fourth sub-bit stream; and performing the second-round of encryption by encrypting the received first operated ciphertext bit stream and the second operated ciphertext bit stream with predetermined second encryption codes an odd number of times and concurrently outputting third and fourth ciphertext bit streams of length n, wherein the third ciphertext bit stream is encrypted a third number of times and the fourth ciphertext bit stream is encrypted the fourth number of times, the fourth number of times exceeding the third number of times, wherein the last encryption for the second ciphertext bit stream in the first-round is performed at the same time of performing the first encryption of the first operated ciphertext bit stream in the second round of encryption.