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digital signature

A message digest of an item that has been encrypted with a subject's private key. Using the public key of the subject and the contents of the original item, the recipient can verify that the item was signed by the subject.

Digital signatures are used to detect whether a certificate has been tampered with or modified.

Verification is done using the public key of the originator and the item itself. The recipient decrypts the signature using the originator's public key, obtaining the message digest of the item.

The recipient then computes its own message digest of the item and compares the two message digests. If they match and the recipient obtained the public key from a reliable source, the recipient is assured that the originator signed the item.