noun
code book
A book containing codes, ciphers, or a set of rules for encoding/decoding messages. Used in cryptography, espionage, and sometimes in programming contexts.
スパイはコードブックを使って暗号を解読した。
The spy deciphered the code using a code book.
Variant with interpunct; less common but seen in some contexts.
Borrowed from English 'code book'.