[jonathrg]

The term to google for more information about this would be Known plaintext attack.

[geor9e]

Oh that makes sense. I assumed wrong that it was going to be about prisoners sending secret messages in their letters home, and the guards wanting to scramble those out.

[01HNNWZ0MV43FF]

And the term for _that_ is steganography

[onionisafruit]

I clicked thinking it was about avoiding watermarks when exfiltrating data. I enjoyed the cryptography lesson I got instead.