Plain text is the raw file which is not encrypted. When the same file is encrypted by using a secret key and encryption algorithm (cipher) then the plain text is converted to cipher text. Relation between plain text and the cipher text is given below:
Encryption: Encryption is the process of converting plain text in to cipher text by the use of secret keys and encryption algorithm.
C = EA(P, EK)
where, C is cipher text, EA is encryption algorithm, P is plain text and EK is encryption key.
Decryption: Decryption is the process of converting cipher text in to plain text by the use of secret keys and decryption algorithm.
P = DA(C, DK)
where, P is plain text, DA is decryption algorithm, C is cipher text and DK is decryption key.
According to Kerckhoffs’s Principle, everything in the encryption process can be made public except for the secret key. That means the encryption and decryption algorithm is made available to all. However, the secret key is the only thing that remains a secret to an outsider.