Patent ID: 8121284

Claim:
An information processing system that performs authentication using hash calculation, wherein said system is configured to: divide a plain text to be encrypted into n (n is a natural number) plain text blocks; set a first set value, which differs for each plain text, in the plain text to be encrypted; perform a hash calculation for a first calculation result which is obtained as a result of a first calculation performed for the first set value and an encryption key to output a first hash calculation result; output a result which is obtained as a result of a second calculation performed for an i-th (i is a natural number satisfying i≦n) hash calculation result and an i-th plain text block as an encrypted i-th cipher text block; and perform a hash calculation for a second calculation result which is obtained as a result of the first calculation performed for the i-th hash calculation result and encryption key to output an (i+1)th hash calculation result.