Introduction to Information Security

Signing the Message

• Alice runs the encryption program on the combination of the private key and the message digest.
• She attaches the result to the e-mail, and sends it to Bob.
• She may also attach the public key.
• This is the signature. To see why it works like a signature, consider what Bob does.

Bob’s Response

• Bob runs the encryption program on the combination of the public key and the message digest.
• Doing so can only decrypt something encrypted with the private key, so, if decryption is successful, the recipient knows the message came from Alice—or, more exactly, someone in possession of Alice’s private key.
• We are assuming that Bob knows that the public key is Alice’s.
• This is the sense in which the message is signed. Like a handwritten signature, the digital signature indicates the message is from the “undersigned.”

More Than A Signature

• Bob then runs the hash function on the message itself. If the result matches the unencrypted message digest, Bob knows that the message was not altered in transmission.
• This is better than a signature, which does not do anything to indicate that the message was not altered in transmission.

Public Keys and Identity

• We assumed that Bob knows that the public key he uses is Alice’s. How does he know this?
• A certification authority verifies that the public key is Alice’s
• Alice has previously registered with the certification authority, at which time she provided proof of her identity.

Computer Systems Security

Data security

Data Security

• Data security is basically the process of keeping certain information private
• It involves the use of various methods to make sure that data is kept confidential and safe
• Data security ensures the integrity and the privacy of data, as well as preventing the loss or corruption of data.