The RSA (Rivest–Shamir–Adleman) cryptographic algorithm, one of the first public-key cryptosystems, used for secure data transmission, was patented in the United States on 20 September, 1983. The RSA patent expired in September 2000, making the algorithm available for public use without the need for licensing or fees.
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The RSA algorithm, one of the world's most widely-used encryption methods, had been developed in 1977.
It was named after its inventors, Ron Rivest, Adi Shamir, and Leonard Adleman, who were researchers at
the Massachusetts Institute of Technology.
Controversy: Many believed the concept of public-key cryptography should be freely available to benefit society. A different cryptographic scheme, known as Diffie-Hellman, was invented earlier and introduced the idea of public-key cryptography, but it wasn’t patented in the same way.