Off line cash card system and method

An electronic fund transfer system for carrying out cash transfer transactions in business and trade sale dealings comprising:

• a plastic card having a magnetic stripe containing information representing an available cash balance and other information including a first enciphering key recorded with no a.c. or d.c. bias and no saturation;
• a transaction cash register machine for register recording an amount of money received and exhibiting an amount of each sale, said transaction cash register machine including
• means for reading said magnetic stripe,
• means for verifying the validity of said card,
• means for verifying that a user of said card is an authorized card bearer,
• means for modifying said cash balance and other information recorded on said magnetic stripe, and
• means for magnetically recording and storing information of each transaction for further processing at a data processing center.

A method of verifying that a user of an electronic fund transfer system card is an authorized card bearer, comprising the steps of:

• (a) upon a first presentation of said card to the system, randomly generating a digital number;
• converting said digital number to an analog signal;
• recording said analog signal onto said card with a random mutation by recording with no a.c. or d.c. bias and no saturation;
• reading said randomly mutated analog signal from said card;
• converting said randomly mutated analog signal to a digital representation thereof;
• and
• using said digital representation as a first enciphering key along with personal identification number (PIN) data supplied by said user as a second enciphering key to encipher onto said card an identifying datum which is uniformly used throughout said system, and
• (b) and upon a subsequent presentation of said card to the system,
• reading said enciphered identifying datum from said card;
• reading said randomly mutated analog signal from said card;
• converting said randomly mutated analog signal to a digital representation thereof;
• and
• using said digital representation as a first enciphering key along with PIN data supplied by said user as a second enciphering key to attempt to decipher said identifying datum,
• whereby a successful deciphering of said identifying datum indicates that said user is an authorized card bearer.

A method of enciphering and recording onto a card information used in an electronic fund transfer system, including an available cash balance, comprising the steps of:

• randomly generating a digital number;
• converting said digital number to an analog signal;
• recording said analog signal onto said card with a random mutation by recording with no a.c. or d.c. bias and no saturation;
• reading said randomly mutated analog signal from said card;
• converting said randomly mutated analog signal to a digital representation thereof;
• using said digital representation as a first enciphering key along with personal identification number (PIN) data supplied by a bearer of said card as a second enciphering key to encipher said electronic fund transfer system information;
• and
• recording said enciphered information onto said card.