So I have an encrypted text file that I know contains the phrase "potatoes are awesome" Is there a way for me to decrypt the text based on me knowing that phrase and the encrypted data? (I also don't know the method of encryption)

Thanks in advance

  • 2
    No, any good modern encryption scheme in a reasonable cipher mode is resistant against known-plaintext attacks. Knowing the ciphertext and a plaintext doesn't let you solve for the used key. But since you didn't specify the encryption algorithm, it can't be said for sure. – Maximilian Gerhardt Jun 8 '17 at 17:59

The answer completely depends on the encryption used, which you said you don't know. Odds are, if it is anything modern, the answer is "no" as one of the comments says. Modern encryption systems are highly resistant to known plain text cryptanlysis.

However, if this were a simple substitution cipher, or even a poly-alphabetic substitution cipher, then "yes," it's likely crack-able.

If the plain text was XOR'ed with a relatively short, repeating key, that too would be possible to crack.

But ultimately, it depends on which crypto was used, and if it is anything reasonably modern and standard, the answer is no.

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