A hardware wallet that never touched the internet just lost 594 BTC. Per Coinkite's own advisory on 30 July 2026, roughly 594 BTC (about $38M) was swept from around 500 single-signature Coldcard wallets in about 25 minutes. The cause was not the airgap. Seed generation fell back to MicroPython's software PRNG instead of the device's hardware RNG. On Mk3 firmware from 4.0.1, that left seeds with roughly 40 bits of entropy instead of 128. Do the arithmetic, because it is the whole story. 40 bits is 1.1 trillion candidate seeds. BIP-39 runs PBKDF2-HMAC-SHA512 at 2048 iterations, so one high-end GPU grinds about 2.4 million candidates a second. That is 5 days on a single card, under 2 hours on 64 of them, and about $60 of rented compute. And you only pay that once. Precompute the space, derive the addresses, keep the table. After that every affected wallet is drained on sight. The 25 minute sweep was not the attack. It was the receipt. Airgapping defends against exfiltration. It does nothing whatsoever about a broken random number generator. Offline is not a security property, it is a threat model, and it says nothing about whether your keys were unguessable in the first place. Worth keeping honest: Mk4 and Mk5 before 5.6.0, and Q before 1.5.0Q, got about 72 bits. That is 4.3 billion times harder than 40 and nobody is cracking it today. But it is not the 128 you were sold. That is margin, quietly spent, and you were never told the balance. If you hold one: firmware fixes generation, not existing seeds. A weak seed is weak forever. Generate a fresh one and move the funds. Wallets behind a BIP-39 passphrase appear largely insulated. The property you cannot see is the one that fails. Verify, do not assume. #Bitcoin #InfoSec #Cryptography #HardwareWallet #SelfCustody
