Can the Same Word Appear Multiple Times in a BIP39 Seed?

Hey folks, I've got a technical question about BIP39. When generating a 24-word seed, is it actually possible for a word to appear more than twice? I know there's a chance for it to repeat, but three times seems wild.

BIP39 doesn't allow a word to show up more than twice in a seed phrase. With over 30 trillion combinations from the 2000+ word list, repeating words just isn't necessary. At least that's what I remember from my readings.

Not sure about that. I think there's nothing stopping a word from appearing multiple times. Sure, having it three times is super unlikely, but it's not impossible.

Wait, are you saying BIP39 has some code to stop words from being repeated more than twice? If that's true, why do wallets let phrases with repeats exist? Like, if you used a word three times, how does that even work?

Right? There's no rule preventing duplicates. You can technically have a word show up multiple times in your seed. So, yeah, a valid wallet can exist even with a word repeated thrice.

Whenever you create a BIP39 seed, it’s based on a random number. So technically, any word can appear more than once, even 3 times or more. But that seems kind of off to me.

Got it. So it's possible but really rare for a wallet to generate a seed with a word appearing three times, right? Just curious if it’s a hard rule or more about probability.

Exactly, it’s theoretically possible. You could even have a single word repeated 24 times in a seed phrase. The odds drop sharply with more repeats, but it can happen.

Thanks for clarifying that.

Glad this topic came up! I thought I knew the answer, but now I realize I was mistaken. So, if we assume that some words are repeated, does that make it easier to guess the seed phrase?

There’s a chance, sure, but it’s still pretty low. Picking from 2048 words makes it less likely to see repeats. But if a seed has a repeating word, it doesn't make it easier to crack.

Just remember, the seed phrase isn't just random words picked; it’s encoded from a random number. If done right, even if words repeat, you’re fine.

Nope, nothing stops repeated words. Just to throw in some numbers: a 12-word seed has a 3% chance for a repeat. A 24-word seed hits about 12.65% for at least two repeats.

You should probably edit your previous reply so you don’t spread that misinformation. A seed phrase with repeated words can still be secure.

Here’s a fun example: a valid seed phrase can have repeating words, and that’s all valid if it meets the checksum.

Haha, yeah! Makes you wonder how often people just roll with those stats and don’t even realize it. I’ve had some 24-word phrases with repeats myself.

For real! I’ve used wallets with repeated words and had transactions. It doesn’t seem to matter much.

But why would brute force crack it so fast? If someone had a phrase like 1500 repeated 23 times, it would take ages to hit that exact combo.

Brute force is about trying combinations, but if someone’s watching for weak seeds, they can sweep funds instantly. Repeated words can make it easier to guess.

That’s a good point. Limiting duplicate words would just make seed phrases less secure. Randomly generated seeds are just fine.