A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents.
A valid digital signature, where the prerequisites are satisfied, gives a recipient a very strong reason to believe that the message was created by a known sender (authentication) and that the message was not altered in transit (integrity).
Digital signatures are like electronic “fingerprints.” In the form of a coded message, the digital signature securely associates a signer with a document in a recorded transaction.
Digital signatures use a standard, accepted format, called Public Key Infrastructure (PKI)
Everything is a combined signature of other things!