RSA is named after its inventors, Rivest, Shamir and
Adelman (though some say Clifford Cocks had formulated the algorithm
some years before Rivest and company went public with it). RSA is the
only example of an asymmetric algorithm that has achieved wide-spread
use.
A symmetric algorithm such as DES uses the same key
for both encryption and decryption. In contrast, an asymmetric algorithm
uses a pair of different but related keys, one for encryption and the
other for decryption.
The advantage of an asymmetric algorithm is that one
key of the pair can be kept secret, and the other can be published.
Therefore, anyone can use the public key to encrypt data, but only the
owner of the corresponding private key can decrypt it.
On the other hand, the owner of the private key can
encrypt data knowing that anyone with access to the corresponding public
key can decrypt it and be sure that only the owner of the private key
could have done the encryption. Thus it is possible to create digital
signatures and thereby achieve non-repudiation (the sender of a
digitally signed document cannot deny that he signed it because only he
has access to the private key).
