Public-Key Cryptography

Public-key cryptography, also called asymmetric cryptography, secures communication using a mathematically linked pair of keys, a public key that can be shared openly and a private key that must be kept secret, so two parties can establish a shared secret or verify a digital signature without ever having exchanged a secret key beforehand. The British cryptographer James Ellis conceived the underlying idea of non-secret encryption at the UK's GCHQ in 1970 without finding a way to implement it, and his colleagues Clifford Cocks and Malcolm Williamson worked out, respectively, what became the RSA algorithm in 1973 and the Diffie-Hellman key exchange in 1974, though this work stayed classified until 1997. The American researchers Whitfield Diffie and Martin Hellman published the same key-exchange idea openly in 1976, the first published practical method for establishing a shared secret key over a channel with no prior shared secret, and Ron Rivest, Adi Shamir and Leonard Adleman independently invented and published the RSA algorithm in 1977 and 1978, using exponentiation modulo the product of two very large prime numbers to encrypt data and create digital signatures.