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Abstract

A technique for reducing RSA (Rivest, Shamir and Adleman algorithm) cryptovariable key from 1200 bits (400-bit public key, 400-bit secret key and 400-bit modulus) to 106 bits makes feasible the storage of the RSA algorithm parameters on current magnetic stripe cards used by the banking and finance industry. Of the 106 bits required, only 56 bits must be kept secret; the remaining 50 bits are nonsecret. These 106 bits are used to derive two 200-bit primes P and Q from which is computed the modulus N=PQ and two 400-bit keys PK (public key) and SK (secret key). In effect, a savings in storage is achieved at the expense of performing a precomputation to derive the modulus and keys each time the system is utilized for encryption/decryption. The 56-bit value plus the additional 50 bits of nonsecret data can be used to generate the RSA cryptovariables in systems where the RSA algorithm has been implemented. In another embodiment, a technique is provided for reducing the RSA cryptovariable storage of the public key PK and modulus from 800 bits to 260 bits. These 260 bits can be used at any later time to derive the 400-bit public key PK and 400-bit modulus N=PQ. The savings in storage is achieved by performing a precomputation each time the system is utilized for encryption/decryption.

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