Digital signature
Alternatively called digitally signed, a digital signature is a mathematical scheme used to verify the authenticity of a digital document or message. They are used when determining authenticity and avoiding tampering are important, such as in financial transactions.
Digital signatures are used as a means to implement electronic signatures that are encrypted. These security measures allow for both authentication and non-repudiation (the signer cannot deny signing a document while claiming his/her private key has not been compromised).
Composition
A digital signature can be broken down into three parts: A key generation algorithm, a signing algorithm, and a signature verifying algorithm. The key generation algorithm selects a random private key from a set of possibilities and sends the private key with a related public key. The signing algorithm produces a signature based on the message and the private key. Finally, the signature verifying algorithm accepts or rejects the authenticity of the message when provided with the message, signature, and public key.