Why was the Coldcard failure possible, and why are Ledger & Trezor different? The issue wasn’t a faulty hardware chip. It was a software bug. Coldcard’s firmware was supposed to generate seeds using the device’s hardware random number generator. Instead, due to a silent fallback in the code, some devices used a much weaker software random number generator seeded from predictable values. As a result, seeds that should have contained 128 bits of entropy ended up with only about 40 or 72 bits. Ledger generates its seed inside a certified Secure Element using a hardware random number generator that is designed and evaluated for cryptographic use. Trezor also relies on a hardware random number generator and, on newer models, combines multiple entropy sources during seed generation. Its open source firmware has been extensively audited by the security community over many years.
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