Authentication in a digital setting is a process whereby the receiver
of a digital message can be confident of the identity of the sender
and/or the integrity of the message. Authentication protocols can be
based on either conventional secret-key cryptosystems like DES or on
public-key systems like RSA; authentication in public-key systems uses
digital signatures.
In this document, authentication will generally refer to the use of
digital signatures, which play a function for digital documents similar
to that played by handwritten signatures for printed documents: the
signature is an unforgeable piece of data asserting that a named person
wrote or otherwise agreed to the document to which the signature is
attached. The recipient, as well as a third party, can verify both that
the document did indeed originate from the person whose signature is
attached and that the document has not been altered since it was
signed. A secure digital signature system thus consists of two parts: a
method of signing a document such that forgery is infeasible, and a
method of verifying that a signature was actually generated by whomever
it represents. Furthermore, secure digital signatures cannot be
repudiated; i.e., the signer of a document cannot later disown it by
claiming it was forged.
Unlike encryption, digital signatures are a recent development, the need for which has arisen with the proliferation of digital communications.