If a message has to be encrypted for secrecy purposes, it is initially present as plaintext. If it is then encrypted according to a specified key, the string of seemingly meaningless characters is called ciphertext.
The ciphertext is created from the plaintext with the help of the cipher. The cipher itself is a bit combination generated from a cryptoalgorithm that cannot be decrypted. The cipher is divided into asymmetric and symmetric ciphers, which are divided into block ciphers and stream ciphers.
The two most common, but also easily broken, encryption methods are the substitution cipher, in which characters are recoded according to a character list, also known as a substitution box, and the transposition cipher, in which letters of a plaintext are rearranged according to a certain scheme.