--- title: "ColdCard’s RNG: what about your passphrase?" url: https://daily.dev/posts/coldcard-s-rng-what-about-your-passphrase--ohtxmzsdw source_url: https://blog.codeminer42.com/coldcards-rng-what-about-your-passphrase type: article source: "The Miners" published: 2026-08-07T12:28:13.685Z updated: 2026-08-07T12:29:51.587Z tags: ["security", "cryptography", "bitcoin"] reading_time: 13 upvotes: 0 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # ColdCard’s RNG: what about your passphrase? **[The Miners](https://daily.dev/sources/miners)** · 13 min read · 0 upvotes · 0 comments ## Summary A deep dive into whether a BIP39 passphrase protected ColdCard users from the firmware RNG bug that collapsed mnemonic entropy to ~2^40. The key insight is that the passphrase and mnemonic search spaces multiply rather than add, meaning the passphrase became the sole security budget once the mnemonic was compromised. A practical offline demo shows two attack scenarios: one without a passphrase (blocked) and one with a weak passphrase wordlist (cracked). A detailed table quantifies cracking time across passphrase strengths and GPU farm sizes, showing that 3+ genuinely random diceware words push cracking time past feasibility even for a 1000-GPU farm, while a PIN or single common word falls within months. The post also warns that the passphrase was designed for physical theft protection, not RNG failures, and that over-complicating it risks self-inflicted fund loss. The recommended action is migrating to a fixed device regardless of passphrase strength. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Does a BIP39 passphrase protect against the ColdCard RNG bug that reduced entropy to 2^40? A BIP39 passphrase multiplies the attacker's search space rather than adding to it, so it only protects you if the passphrase itself carries enough entropy. With the ColdCard Mk2/Mk3 mnemonic collapsed to ~2^40, a 4-digit PIN or single common word falls to a 1000-GPU farm in months, while 3+ genuinely random diceware words (~39 bits) push cracking time past feasibility even for that farm. The passphrase does not fix the broken mnemonic; migrating to a fixed device is still required. _Developers and Bitcoin holders tracking the ColdCard vulnerability and its mitigations follow the latest analysis on daily.dev._ ### How fast can an RTX 5090 crack BIP39 wallets using PBKDF2-HMAC-SHA512? An RTX 5090 performs approximately 1.4 million BIP39 derivations per second. The hashcat benchmark clocks ~4.2 million/s for PBKDF2-HMAC-SHA512 at 999 iterations; at BIP39's 2048 iterations that drops to ~2 million/s, and deriving the key and address reduces it further to around 1.4 million/s. A farm of 1000 such GPUs can sweep the ~2^40 ColdCard Mk2/Mk3 space in roughly 13 minutes. _Those choosing hardware wallets or evaluating passphrase strength against modern GPU farms find the latest benchmarks and security research on daily.dev._ ### What is the difference between how a BIP39 passphrase enters the seed derivation versus the mnemonic? The BIP39 passphrase is used as the salt in a PBKDF2-HMAC-SHA512 function, while the mnemonic is the password input. The formula is: seed = PBKDF2(HMAC-SHA512, password=mnemonic, salt='mnemonic'+passphrase, 2048 iterations, 64 bytes). Because the passphrase is typed after generation and never passes through the RNG, an RNG bug affects only the mnemonic's entropy, not the passphrase's. _Developers building or auditing Bitcoin key derivation pipelines keep up with BIP39 implementation details on daily.dev._ --- Tags: [#security](https://daily.dev/tags/security), [#cryptography](https://daily.dev/tags/cryptography), [#bitcoin](https://daily.dev/tags/bitcoin) [View this post on daily.dev](https://daily.dev/posts/coldcard-s-rng-what-about-your-passphrase--ohtxmzsdw)