RSA is an asymmetric algorithm for public key cryptography, widely used in electronic commerce. The algorithm was described in 1977 by Ron Rivest, Adi Shamir and Len Adleman; the letters RSA are the initials of their surnames.

Clifford Cocks, a British mathematician working for GCHQ, described an equivalent system in an internal document in 1973. His discovery, however, was not revealed until 1997 due to its top-secret classification.

The security of the RSA system relies on the difficulty of factoring very large integers. New fast algorithms in this field could render RSA insecure, but this is generally considered unlikely.

The algorithm was patented by MIT in 1983 in the United States of America. The patent expired 21 September 2000. Since the algorithm had been published prior to the patent application, it could not be patented in other countries.

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