Encrypted texts are intended to prevent the contents from being read by anyone. One way to find out how texts have been encrypted is the Chosen plaintext attack.
What is a Chosen plaintext attack?
A Chosen Plaintext Attack is a term used in cryptanalysis. The attack is used to find out the properties of an algorithm for encrypting texts using arbitrary, unencrypted plaintexts. The most famous plaintext attacks were carried out by Allied cryptanalysts during World War II against the German Enigma cipher machines.
How does a Chosen plaintext attack work?
In a plaintext attack, the attacker can provide arbitrary text consisting of, for example, just one “a”, two “aa”, and so on. Depending on the ciphertext method used, it is very easy to extract the key length from the ciphertext and recover the key if the text is just letters strung together.
In this type of attack, the attacker selects different plaintexts for encryption. Instead of using one large block of text, smaller blocks of text are entered. The outputted cipher text is evaluated and then based on the response another text is selected and so on. This approach allows the attacked system to be examined closely.
In the Known Plaintext Attack, the attacker knows at least one sample of both the plaintext and the ciphertext. For example, if the XOR cipher is used, the key is displayed as plaintext-XOR ciphertext.
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