| 摘要 |
<P>PROBLEM TO BE SOLVED: To verify validity of a received ciphertext before trying to decipher it. <P>SOLUTION: A memory unit 3 has stored a safety command and safety data which are confirmed to be safe. A determination unit 4 selects a safe command and safe data expected to be included in a plaintext of a received ciphertext based on the trace of a communication sequence when it has received the ciphertext from a communication partner device after having shared keys with the communication partner device; generates a communication text which is expected to be equivalent to the plaintext of the received ciphertext using the selected safety command and safe data. An encryption unit 5 encipher the communication text using the keys shared with the communication partner device. The determination unit 4 generates a digest by performing one-way calculation to the ciphertext and also generates a digest by performing one-way calculation to the received ciphertext and then mutually compares the digests. If the digests accord, the received ciphertext is safe and the encryption unit 5 deciphers the ciphertext. <P>COPYRIGHT: (C)2012,JPO&INPIT |
