CompTIA Security+ Question E-97

Which of the following would provide the STRONGEST encryption?

A. Random one-time pad
B. DES with a 56-bit key
C. AES with a 256-bit key
D. RSA with a 1024-bit key

Answer: A

One-time pads are the only truly completely secure cryptographic implementations.

They are so secure for two reasons. First, they use a key that is as long as a plaintext message. That means there is no pattern in the key application for an attacker to use. Also, one-time pad keys are used only once and then discarded. So even if you could break a one-time pad cipher, that same key would never be used again, so knowledge of the key would be useless.