An introduction to cryptanalysis

Cryptanalysis is defined as the process of attempting to find a shortcut method, not envisioned by the designer, for decrypting an enciphered message when the key used to encrypt the message is not known. As an example, this paper cryptanalyzes a simple substitution cipher. The methods of cryptanalysis used are the chosen-plaintext attack, the known-plaintext attack, and the ciphertext-only attack, which are defined and discussed in the paper.