Interlock Protocol - How IT Works

How It Works

The Interlock protocol works roughly as follows: Alice encrypts her message with Bob's key, then sends half her encrypted message to Bob. Bob encrypts his message with Alice's key and sends half of his encrypted message to Alice. Alice then sends the other half of her message to Bob, who sends the other half of his. The strength of the protocol lies in the fact that half of an encrypted message cannot be decrypted. Thus, if Mallory begins her attack and intercepts Bob and Alice's keys, Mallory will be unable to decrypt Alice's half-message (encrypted using her key) and re-encrypt it using Bob's key. She must wait until both halves of the message have been received to read it, and can only succeed in duping one of the parties if she composes a completely new message.