Shared symmetric key

Definition
In shared symmetric key approaches, the user signs a document and verifies the signature using a single key (consisting of a long string of zeros and ones) that is not publicly known, or is secret.

Overview
Since the same key does these two functions, it must be transferred from the signer to the recipient of the message. This situation can undermine confidence in the authentication of the user's identity because the symmetric key is shared between sender and recipient and therefore is no longer unique to one person. Since the symmetric key is shared between the sender and possibly many recipients, it is not private to the sender and hence has lesser value as an authentication mechanism.

This approach offers no additional cryptographic strength over digital signatures. Further, digital signatures avoid the need for the shared secret.