I gave ChatGPT a cryptographic signature scheme I developed and it found a way to forge signatures as my scheme was insecure. I thought ChatGPT was wrong because I didn't read the attack carefully enough and I didn't expect it be able to reason about cryptography that well. I asked a human cryptographer and then pointed out the same flaw but it took them slightly longer.

To me it felt like knowledge creation, but maybe someone had already published a similar scheme and then someone had published a similar attack and ChatGPT was pattern matching on that and adapting it to my setting. That seems very likely because while I was working in RSA, the fix to the attack is very similar to the use of a nonce in Schnorr signatures and for the same reason.