Known plaintext attack

In cryptography, the known plaintext attack, or KPA, is an attack based on having samples of both the plaintext and corresponding encrypted or ciphertext for that information available. This information is used to conduct an analysis of the data in order to determine the secret key used to encrypt and decrypt the information. Historical ciphers are very susceptible to the attack, while modern-day ciphers are less prone to being cracked using the method.