Abstract: A method for transmitting ciphered information between two stations while using session keys. According to the method a mutual identification of the stations (AK, A; A,B) is obtained while using an identification device (ID) comprised in each station. Number values (r.sub.1, r.sub.2), originating from each station, may be exchanged by said identification in a form which is so ciphered that the number values may be recovered by the counterpart only. The session key (t.sub.m) is formed on basis of said number values in a modification device (MODIFI). Ciphered data messages are exchanged between the station using the established session key and a message ciphering/deciphering device (MCRY, MDECRY) comprised in each station. According to the method the mutual identification and the establishment of the session key via an open channel may be obtained by transmitting one separate identification sequence in each direction.

Abstract: A method and apparatus for verifying that the bearer of a card (e.g., credit card, bank card, etc.) is authorized to use the card. The card bears machine-readable indicia of an account number (PAN) and the bearer of the card has memorized a personal identification number (PIN). There is associated with the PAN a check number (PCN) which is derived by (1) generating a first cipher Y1 by encrypting the PAN using the PIN in combination with a secret security number as a key, the bits of which address a data encryption process; (2) generating a second cipher by decrypting the first cipher using the secret security number as a key so that the decryption process is the reverse of the encryption process; and (3) storing the second cipher as the check number PCN in a machine-accessible location, which may be in a separate memory or recorded on the card itself.