Source : Free On-Line Dictionary of Computing

RSA encryption
     
         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 inverse, d, mod (p-1)(q-1),
        which means that 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://www.rsa.com/rsalabs/faq/faq_home.html)}.
     
        (2002-03-29)