Abstract: PROBLEM TO BE SOLVED: To provide a cipher communication system capable of decrypting encrypted ciphers and reducing the cost for management and distribution of keys by providing the system with a key formation means, an encryption means for forming ciphertext by encryption of plaintext and transmitting the formed ciphertext and a cryptoanalysis means for cryptoanalyzing the transmitted ciphertext. SOLUTION: An encryption section 143 forms the ciphertext by encrypting the plaintext read out by using a prescribed encryption algorithm and outputs an instruction for starting the cipher transmission to a transmission and reception section 145. The key formation section 112 of a cryptoanalysis device 110 of a level 1 outputs a calculated integer b1 as a decryption key to a data storage section 114, outputs an integer a1 as an encryption key and the calculated n1 to a transmission and reception section 111 and transmits the decryption key, etc., through the communication circuit 161 to the key formation section 112 of the cryptoanalysis device 110 of the level 1. A cryptoanalysis section 123 forms the common key by using the decryption key 127 received from an input section 125 and the cipher common key, cryptoanalyzes the ciphertext by using the formed common key and forms the plaintext.