In light of the catastrophic low-entropy bug in Coldcard hardware wallets, linked to publicly observed thefts beginning on July 30, Bitcoin holders have started to re-evaluate the trust assumptions in their hardware wallet setups.
How Coldcard’s entropy flaw worked
The Coldcard devices were equipped with apparently functional STM32 “true random number generators” (TRNGs) that rely on physical processes to produce an unguessable seed phrase.
However, after Coldcard creator NVK decided to initiate a firmware rewrite to switch from a GPL-licensed free software model to a read-only model, a serious vulnerability appears to have been introduced.
Starting with firmware version 4.0.1, released in March 2021, the device used MicroPython’s Yasmarang PRNG instead of properly using the STM32 hardware RNG.
Random number generation is an unsolvable problem in computer science, which is why the generation of secure, unguessable private keys…
