How secure is your Bitcoin wallet's mnemonic seed phrase?
19 comments
·July 11, 2025tombennet
brudgers
I could not help but think of a class of early internet scam websites offering to check if your credit card number was stolen.
I'm sure that you aren't just collecting wallet seeds, but that's what it reminds me of.
tombennet
Thanks - I appreciate the comment. It's a valid concern, and one I thought about while making this. Just to clarify a few things:
- I've explicitly discouraged entering a real mnemonic, in several places. In fact I tried to steer people in a safe direction by putting the random generation component first. The article works best when starting with random entropy.
- All the BIP39 logic is handled client-side using paulmillr/scure-bip39, a minimal audited library.
- It works fully offline - no backend, no database, no server calls.
- There are no cookies or tracking scripts beyond simple pageview stats via Plausible (which is privacy-focused)
That said, I’d genuinely welcome suggestions on how to make it more trustable. Do you think open-sourcing the code for the page/site would help?
jbermudes
I think you did enough due diligence by putting the random part first, but I suppose one way to stop someone from putting in a real BIP39 mnemonic would be to use a completely different set of words than those allowed in BIP39.
sparkie
Can you explain why this is a valid mnemonic?
bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon bacon baconatoav
The first question you should ask yourself when tasked to secury literally anything is the same: secure it against whom or what?
This article is about entropy and mostly an explaination why your mnemonic seed is already safe against wild guesses. The question then is how to secure it against attackers who might want to get it otherwise.
If you live alone writing it on a piece of paper and putting it into a locked drawer might literally be enough, since your main concern would probably be online aftacks. If you have 30 guests a week that calculation might change, but then your scenario is to protect against a guest who A) knows you have a lot of bitcoins, B) posseses all other required information to access the wallet and C) is invited or has broken into your flat. If the latter is an issue, maybe getting a decent door and a safe is a good idea.
This is just an example, but if you want to secure a thing, knowing which attack-vectors to secure it against is key.
gblargg
Safest way to generate seed words is a set of dice and printed table. It's odd they only encode 256 bits of entropy, which clearly isn't enough to make multiple 256-bit private keys.
Calwestjobs
just XOR two photos from your iphone and pick middle part of that... you can even sha512 that.
Maybe Subkey generation ?
Calwestjobs
Maaan, i stopped paying attention to bitcoin after Bitcoin Cash fork fiasco. Everything flew back into my consciousness. eth DAOHACK fail. Website, listing all possible BTC private keys. (de)Dusting. Printing signed transactions offline into QR codes on thermal paper... Good old days.
I am not sure BTC is still worth the hassle, most of hashrate is inside of USA (70+% =>51%...). most of BTC holdings is in USA... btc saga will end soon and badly in my opinion. BTC Cash made me pessimistic.
In Europe they have SEPA Instant Credit Transfer which allows people inter bank transfers in under 15 seconds. All KYC, all legal, all gov approved, gov regulated, all without fees to btc exchange / VISA. BTC does not even makes sense anymore. Technological innovations flew right past the BTC.
i am not even sure BTC infrastructure is quantum safe, blockchain "is", but i doubt rest of infrastructure is...
npoc
You're missing its monetary fundamentals that make it the hardest asset mankind has ever seen.
tomschwiha
I'm totally not into Bitcoins but nice and interesting writeup. I very much like the interactivity of the article.
Calwestjobs
Yeah, Jupyter notebooks / literate programming for everything !
udev4096
Shit posts making top of the HN, again. Are people really that stupid?
Hey, author here. I made this to help technically curious people understand what's really going on when they're handed a Bitcoin seed phrase (i.e. why it's not just a password). You can flip bits of entropy, explore checksum validation, and see how mnemonic phrases are turned into deterministic wallets. Feedback welcome. If anything breaks I’ll fix it fast.