$ cryptanalysis
1. (I) The mathematical science that deals with analysis of a cryptographic system to gain knowledge needed to break or circumvent the protection that the system is designed to provide. (See: cryptology, secondary definition under "intrusion".)
2. (O) "The analysis of a cryptographic system and/or its inputs and outputs to derive confidential variables and/or sensitive data including cleartext." [I7498-2]
Tutorial: Definition 2 states the traditional goal of cryptanalysis, i.e., convert cipher text to plain text (which usually is clear text) without knowing the key; but that definition applies only to encryption systems. Today, the term is used with reference to all kinds of cryptographic algorithms and key management, and definition 1 reflects that. In all cases,
however, a cryptanalyst tries to uncover or reproduce someone else’s sensitive data, such as clear text, a key, or an algorithm. The basic cryptanalytic attacks on encryption systems are
ciphertext-only, known-plaintext, chosen-plaintext, and chosenciphertext; and these generalize to the other kinds of cryptography.