noun
cipher key; code key
A key used to decrypt or encrypt a cipher or code.
暗号解がなければ、この暗号文は読めない。
Without the cipher key, this ciphertext cannot be read.
鍵 is the general word for 'key', but in cryptographic contexts 暗号解 is a more technical term for a cipher key.
Compound of 暗号 (cipher) and 解 (solution, key). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning 'cipher key'.