Which algorithm uses a key that is as long as a plaintext message and the keys are used only once. Cryptography Which algorithm uses a key that is as long as a plaintext message and the keys are used only once. a. IDEA b. Blowfish c. One-Time Pads d. Twofish Answer: c. One-Time Pads Learn More : Share this Share on FacebookTweet on TwitterPlus on Google+