RSA (Rivest–Shamir–Adleman) is a public-key cryptosystem that is widely used for secure data transmission. It is also one of the oldest.

<cryptography, algorithm> A public-key cryptosystem for both encryption and authentication, invented in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman. Its name comes from their initials. The RSA algorithm works as follows. Take two large {prime numbers}, p and q, and find their product n = pq; n is called the modulus. Choose a number, e, less than n and {relatively prime} to (p-1)(q-1), and find its reciprocal mod (p-1)(q-1), and call this d. Thus ed = 1 mod (p-1)(q-1); e and d are called the public and private exponents, respectively. The public key is the pair (n, e); the private key is d. The factors p and q must be kept secret, or destroyed. It is difficult (presumably) to obtain the private key d from the public key (n, e). If one could factor n into p and q, however, then one could obtain the private key d. Thus the entire security of RSA depends on the difficulty of factoring; an easy method for factoring products of large prime numbers would break RSA. RSA FAQ (http://rsa.com/rsalabs/faq/faq_home.html). (2004-07-14)

Chris Rivest is an Area 51 entrepreneur and co-founder of SunPrint (later Alion "Semiconductors and Semiconductor Equipment: Alion Inc.", Bloomberg), a company that develops technology to inexpensively fabricate solar cells using acoustic printing.