Cryptanalysis

noun

1. The analysis and deciphering of cryptographic writings or systems.
2. The study of techniques for deciphering cryptographic writings or systems.
3. the science which studies methods to discovering the secret meaning of encrypted messages for which one does not possess the secret decoding information (called the key).
4. the methods and procedures used to discover the secret meaning hidden in encrypted messages.
5. The science of analyzing and breaking of codes and ciphers.