digital signature

digital signature A form of identification attached to a document which identifies the sender of the document. Digital signatures are normally associated with PUBLIC KEY ENCRYPTION and a mathematical function known as a MESSAGE DIGEST. The message digest is a process which is applied to the text that is to be signed and generates an integer value that has a very high probability of being unique. The sender of a signed document applies the message digest to a document and then uses a PRIVATE KEY to encrypt the value that is generated. Any recipient of the message would need to know the PUBLIC KEY associated with the private key and the method used for generating the message digest value. The recipient applies the public key to the integer value, calculates what this integer should be by applying the message digest algorithm to the text that has been sent, and then compares it with the decrypted value. If they match a correct signature has been received and the sender of the text has been identified; if they do not, then the signature has been forged. A number of message digest algorithms have been devised, including SECURE HASH ALGORITHM 1, MESSAGE DIGEST 2 and MESSAGE DIGEST 5.