AntraSOFT

DIGITAL SIGNATURE technology in details.

Bob

(Bob's public key)

(Bob's private key)

Bob has been given two keys. One of Bob's keys is called a Public Key, the other is called a Private Key.

Bob's Co-workers:
			Anyone can get Bob's Public Key, but Bob keeps his Private Key to himself
Pat	Doug	Susan

Bob's Public key is available to anyone who needs it, but he keeps his Private Key to himself. Keys are used to encrypt information. Encrypting information means "scrambling it up", so that only a person with the appropriate key can make it readable again.

Susan (shown below) can encrypt a message using Bob's Public Key. Bob uses his Private Key to decrypt the message. Any of Bob's coworkers might have access to the message Susan encrypted, but without Bob's Private Key, the data is worthless. Either one of Bob's two keys can encrypt data, and the other key can decrypt that data.

"Hey Bob, how about lunch at Taco Bell. I hear they have free refills!"

HNFmsEm6Un BejhhyCGKOK JUxhiygSBCEiC 0QYIh/Hn3xgiK BcyLK1UcYiY lxx2lCFHDC/A

HNFmsEm6Un BejhhyCGKOK JUxhiygSBCEiC 0QYIh/Hn3xgiK BcyLK1UcYiY lxx2lCFHDC/A "Hey Bob, how about lunch at Taco Bell. I hear they have free refills!"

With his private key and the Secure Messenger software, Bob can put digital signatures on documents and other data. A digital signature is a "stamp" Bob places on the data which is unique to Bob, and is very difficult to forge. In addition, the signature assures that any changes made to the data that has been signed can not go undetected.

To sign a document, Bob's Secure Messenger software will crunch down the data into just a few lines by a process called "hashing". These few lines are called a message digest. (It is not possible to change a message digest back into the original data from which it was created.)

Bob's Bob's Secure Messenger software then encrypts the message digest with his private key. The result is the digital signature.

Finally, Bob's Secure Messenger software appends the digital signature to document. All of the data that was hashed has been signed.

Bob now passes the document on to Pat.

First, Pat's Secure Messenger software decrypts the signature (using Bob's public key) changing it back into a message digest. If this worked, then it proves that Bob signed the document, because only Bob has his private key. Pat's Secure Messenger software then hashes the document data into a message digest. If the message digest is the same as the message digest created when the signature was decrypted, then Pat knows that the signed data has not been changed.