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Developer posts secret key on GitHub, loses $40K in 2 minutes
(cointelegraph.com)
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That's not quite the definition of known plaintext attack (cryptography nerd here), that's bruteforce with a "crib" to use older terminology (known patterns which allows you to test candidate keys).
A known plaintext attack is defined as an attack on the algorithm to extract the key faster than bruteforce with analytical attacks.