Posts tagged #Randomness
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The number used only once
Every digital signature consumes, besides the key, a second secret number generated for the occasion and good only once: the nonce. If it repeats, two signatures give back the private key with a subtraction: it happened to the PlayStation 3 and to Bitcoin wallets on Android in 2013. How the recovery works in ECDSA and in Schnorr, shown on the bytes of real signatures; why a nonce that is merely predictable betrays as well; and the point that concerns Bitcoin: a node validates a signature born from a disastrous nonce like any other, consensus cannot notice.
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How big is «practically impossible»?
«It is practically impossible for someone else to generate your own seed» sounds like a way out, and anyone who does not buy it deserves an answer rather than reassurance. How big the space a Bitcoin wallet's seed comes from really is, why the right question is not whether someone guesses yours but whether two identical seeds will ever turn up among all the seeds ever generated, what it would cost a perfect machine just to count them, what difference twelve words instead of twenty-four actually makes, and what a passphrase adds. The fragile point is not the coincidence but the birth, which is to say the generator: the Android episode of 2013 and the Coldcard defect of July 2026.