Cryptanalysis

Cryptanalysis is the study and practice of recovering plaintext or secret keys from encrypted data without authorized access to the key. It examines how encryption systems can be analyzed and broken.

Ciphertext-only attack: An attack that attempts to recover plaintext or a key using only encrypted messages. It shows the limits of analysis when the attacker has no known plaintext or encryption access.
Cryptography: The study and practice of securing information through mathematical techniques, including encryption and authentication. Cryptanalysis examines the security of the systems cryptography constructs.
Frequency analysis: A technique that uses the unequal frequencies of symbols in language to infer substitutions in encrypted text. It is a foundational method for breaking simple substitution ciphers.
Differential power analysis: A side-channel attack that uses statistical analysis of a device's power consumption to infer secret data. It extends key recovery beyond ciphertext by exploiting physical traces of cryptographic computation.
Steganography: The practice of concealing the existence of a message within an ordinary-looking medium. It hides communication itself, whereas cryptanalysis targets the content of encrypted communication.
Known-plaintext attack: An attack that uses one or more matching plaintext and ciphertext pairs to recover information about encryption. Known message fragments can reveal key structure or expose weaknesses in a cipher.
Cipher: A method for transforming readable information into an encoded form and, usually, back again. A cipher defines the transformation whose structure cryptanalysis investigates.
Al-Kindi: A ninth-century Arab polymath who wrote an early surviving systematic account of cryptanalysis. His treatise described frequency analysis as a way to solve substitution ciphers.
Side-channel attack: An attack that infers secret information from a system's physical or operational behavior rather than its intended outputs. It broadens cryptanalysis to timing, power use, and other implementation leakage.
Cryptanalysis of the Enigma: The collection of methods used to recover German Enigma keys and read intercepted Enigma traffic. This named case illustrates cryptanalysis against a specific historical cipher system.

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