Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1994-11-14
1998-04-28
Gregory, Bernarr E.
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 4, 380 9, 380 23, 380 25, 380 30, 380 48, 380 49, 235380, H04L 908, H04L 930, H04L 900
Patent
active
057455716
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a cryptographic method and system and, in particular to a smart card and method of initialising a smart card.
Cryptographic techniques are used to encrypt and decrypt sensitive communications between two terminals. A particular problem exists in ensuring secure communications between credit cards and a central processing station, or host, and the problem becomes more acute with respect to smart cards which are intended to transmit and receive sensitive data. Conventional encryption techniques require that the smart card have a secret key before any sensitive data can be loaded onto the card. Present solutions for smart cards are usually based around one of two techniques. The first involves loading the card with secret information through a physically secure communications channel, which unfortunately is not always practical. The second technique involves relying on the card manufacturer to place an initial secret key on the card, and the card owner then uses the secret key to load the sensitive data required for card applications. Unfortunately, the card manufacturer then has at its disposal all of the information necessary to decipher communications with the card and to recover any secret information loaded on the card.
European patent publication 138,386 describes a system for smart card communication with a host where the encryption and decryption keys are generated internally by the card and the host on the basis of a random number generated by the host and a pre-assigned code number PN allocated to the card. The system, however, again suffers from the disadvantage that the pre-assigned code number needs to be stored in the card on manufacture or else it must be placed on the card in a physically secure environment. If the pre-assigned code number PN cannot be transferred in a physically secure environment, then there is a risk it may become known to someone other than an authorised user. The card could then be used in an unauthorised manner by simply providing an appropriate random number to the card, once the PN and logic used to generated the encryption key are known. It is therefore advantageous to provide a system which could be used for smart cards, and which does not require any third party to be provided with information from which an encryption key can be simply derived or a secure environment within which a pre-assigned code number must be transferred.
Most encryption techniques use a key which is generally a large number on which the encryption and decryption processes are based. Public key encryption techniques, where the transmitting terminal employs a public key to encrypt the transmitted data, and the receiving terminal uses a secret key to decrypt the data, have been found to be particularly advantageous. Data can be readily encrypted without requiring a secret key, yet encrypted communications cannot be intercepted and then decrypted without knowledge of the secret key. The secret key needs to be such that it is related to the public key but cannot be efficiently derived from the public key. An encryption method which uses such a public key and secret key technique is known as the RSA method, and is described in U.S. Pat. No. 4,405,829. According to the RSA method, a message M is encrypted into ciphertext C using the following: to (p-1)(q-1). The message, or plaintext, is reconstructed from the transmitted ciphertext using the following: modulus n are used as the public key and the primes p and q and exponent d are kept secret and constitute the secret key. Provided n is made sufficiently large, such as 512 bits, the primes cannot be efficiently determined from n. The RSA method, however, is computationally intensive and is primarily suitable for powerful processing systems.
Public key techniques or algorithms, being computationally intensive have been considered too slow to execute and requiring too much memory in order to be practical for use on smart cards without additional specialised hardware. Most smart cards have very limited memory for both da
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Gregory Bernarr E.
Telstra Corporation Limited
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