Importance

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Abstract

A method of secure data transmission commences at a sending or originating terminal by processing a sender challenge on an originating subscriber card with a secret originating subscriber coding key to obtain an originating subscriber response. The response is used at the originating terminal to encrypt the message to be securely transmitted. The thus-encrypted message is transmitted, together with the sender challenge in its original form, to a system server. The server retrieves the originating subscriber coding key from a repository to which it has access, and uses the key to generate a response that is identical to that produced by the originating subscriber. It then employs the so-obtained response to decrypt the originator's encrypted message, determines the intended recipient, and retrieves from the repository the coding key assigned to such recipient. The server then issues a new challenge and repeats the above processing and encryption steps using the recipient's subscriber's coding key, thereby re-encoding the message and sending the thus re-encrypted message and the unencrypted new challenge to the receiving station where the same process is employed on the recipient subscriber card to obtain, from the unencrypted new challenge and the recipient subscriber code key stored on the recipient subscriber card, the receiving subscriber response to be used in decryption of the received, server re-encrypted message.

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First Claim