/ˌkrɪptəˈnæləsɪs/
noun — "the study and practice of analyzing and breaking cryptographic systems."
Cryptanalysis is the discipline concerned with examining cryptographic algorithms, ciphers, and encoded messages to uncover hidden information without access to the secret key. It combines mathematics, logic, computer science, and pattern recognition to discover weaknesses, reconstruct plaintext, or recover keys. Cryptanalysis is essential both for testing the security of encryption systems and for legitimate intelligence or historical codebreaking efforts.
Technically, cryptanalysis involves techniques such as:
- Frequency analysis — studying the statistical occurrence of symbols or patterns in ciphertext to infer plaintext or key structures.
- Known-plaintext attacks — leveraging pairs of known plaintext and corresponding ciphertext to deduce keys.
- Chosen-plaintext or chosen-ciphertext attacks — deliberately selecting inputs to observe outputs, exposing vulnerabilities.
- Brute-force attacks — systematically testing all possible keys, often computationally intensive.
- Mathematical attacks — exploiting algebraic, number-theoretic, or combinatorial properties of the encryption algorithm.
# conceptual example: frequency analysis on simple substitution cipher
ciphertext = "KHOOR ZRUOG"
# count letter frequencies
freq = {letter: ciphertext.count(letter) for letter in set(ciphertext)}
# map high-frequency letters to expected letters in English
# e.g., 'R' -> 'E', 'O' -> 'O', etc.
# derive key and decrypt message
Conceptually, cryptanalysis is the art of finding hidden patterns and exploiting weaknesses in the structure of ciphers. It treats encrypted data not just as random symbols but as a puzzle with logical or statistical clues. Success in cryptanalysis often depends on clever heuristics, historical knowledge of cipher design, computational resources, and sometimes intuition.
Historically, cryptanalysis has had a profound impact, from deciphering the Enigma-encrypted messages with the Bombe to modern-day efforts in testing the security of AES, RSA, and other cryptographic standards. It informs the design of robust ciphers by identifying vulnerabilities before adversaries can exploit them.
In practice, cryptanalysis is a cornerstone of cybersecurity, cryptography research, intelligence analysis, and digital forensics. Understanding it allows engineers and researchers to anticipate potential attacks, improve encryption schemes, and ensure data confidentiality and integrity.
See Cipher, Codebreaking, Bombe, Enigma, Encryption.