Encryption and authentication method and circuit for synchronous

Details Encryption and authentication method and circuit for synchronous Encryption and authentication method and circuit for synchronous

1995-07-31

1998-10-20

Gregory, Bernarr E.

Cryptography

Particular algorithmic function encoding

Nbs/des algorithm

380 9, 380 23, 380 28, 380 49, 380 50, 235380, H04L 900

Patent

active

058258825

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Present-day chip cards may be divided into two broad categories: synchronous cards that use wired logic and have their operation controlled by an external clock signal; the clock signal is given by a card reader into which the card is inserted; and asynchronous cards that comprise a microprocessor and have an internal operation that is broadly independent of the reader.
Microprocessor cards enable numerous applications since the working of the card depends solely on the programs that will be incorporated into the card. These programs may be highly variable, depending on the application envisaged. On the contrary, synchronous cards are designed, in principle, for only one application.
A typical example of a synchronous cards is a prepaid phonecard that can be used to consume a certain number of phone-call time units, paid for in advance when the card is purchased. The main functions of the wired logic of the card are the reception of pulses coming from the reader and representing the units consumed, the programming of successive memory cells from these pulses and the transmission, to the reader, of information on the balance available.
Examples of microprocessor cards are access cards to reserved places, bank cards etc. and, more generally, cards used in many applications where the security of information plays a important role. This security is then governed by specific programs incorporated into the card.
The security of use of the card is notably provided by programs to authenticate the bearer, namely programs ascertaining that the bearer of the card is really authorized to use it or, again, programs to authenticate the card, namely programs ascertaining that the card is a genuine card and not a fraudulently manufactured or fraudulently modified card.
Cryptographic programs are provided in the microprocessor cards to carry out these functions of authentication, but this is not so for synchronous cards. Indeed, the reason why synchronous cards continue to be used, even though by construction they offer far fewer possibilities than microprocessor cards, is that they are far less costly: their simple wired logic takes up a far smaller surface area of silicon than a microprocessor and its peripherals. However, if a synchronous card has to be provided with cryptographic computation functions similar to those used in microprocessors, the cost increase would obviate the value of these cards.
However, it is becoming increasingly necessary to plan for security against fraudulent activity even with respect to synchronous cards. Indeed, precautions need to be taken against two possibilities: firstly the fraudulent simulation of a genuine chip card by a dummy or by a personal microcomputer connected to the card reader; the dummy or the microcomputer gives signals that are expected by the reader and lets the reader believe that it is in the presence of a genuine card and secondly, precautions must be taken against the manufacture of spurious cards which are, in all respects, identical to the genuine ones.


SUMMARY OF THE INVENTION

The invention proposes the making of synchronous cards comprising wired logic means that are very simple and inexpensive but, at the same time, highly efficient in order to carry out functions of authentication guaranteeing the right to use the card.
In its general principle, the invention uses a procedure similar to the one used for microprocessor cards: the reader, for example, sends the card a random binary code. The card carries out an internal computation on the basis of this code and of secret data that it contains in its memory. The result is sent to the reader which, for its part, has carried out the same computation on the basis of, the same data elements (the reader knows the secret data elements of the card, or at least it is able to reconstitute them), and the results are compared in the reader to authenticate the card and hence validate its use.
However, what gives the invention its specific character is the fact that the computation made by the c

REFERENCES:
patent: 4064558 (1977-12-01), Hughes et al.
patent: 4087626 (1978-05-01), Brader

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