What does it mean that the security of 256-bit ECDSA, simply click youtu.be and therefore Bitcoin keys, is 128 bits? Mike Schmidt: Last question from the Stack Exchange is, "What does it mean that the security of 256-bit ECDSA, and therefore Bitcoin keys, is 128 bits? I’m not doing a great job of explaining this right now, but yes, oftentimes there is a quadratic reduction of the security due to algorithms and what sort of attack model or threat scenario you’re applying, and I think this happens to be the case here. But if you’re trying to replicate a hash by knowing when you know the input message before the hash, the pre-image, then it’s only a 128-bit security because you sort of have to find two things that produce the same digest rather than needing to replicate one digest. Because, if you try to replicate a hash, an exact hash, without knowing the input, I think you do have 256-bit security.
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