Suppose Ramesh wants to send a signed message to Naresh. He creates a message digest by using a hash function on the message. The message digest serves as a “digital fingerprint” of the message if any part of the message is modified, the hash function returns a different result. Ramesh then encrypts the message digest with her private key. This encrypted message digest is the digital signature for the message.

Ramesh sends both the message and the digital signature to Naresh. When Naresh receives them, he decrypts the signature using Ramesh’s public key, thus revealing the message digest. To verify the message, he then hashes the message with the same hash function Ramesh used and compares the result to the message digest he received from Ramesh. If they are exactly equal, Naresh can be confident that the message did indeed come from Ramesh and has not changed since she signed it. If the message digests are not equal, the message either originated elsewhere or was altered after it was signed.

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