在密码学中，密文（英语：ciphertext或cyphertext）是明文经过加密算法所产生的。因为密文是一种除非使用恰当的算法进行解密，人类或计算机不可以直接阅读理解的明文的形态，所以可以被理解为加密的信息。解密与加密是相对的，即一种使密文转化为明文的过程。

In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. Decryption, the inverse of encryption, is the process of turning ciphertext into readable plaintext. Ciphertext is not to be confused with codetext because the latter is a result of a code, not a cipher.