Have you ever been prompted by your Bitcoin wallet to write down your 12 word or 24 word seed phrase? Have you ever wondered what the difference is between the two of them? Have you ever wondered “Can someone guess my seed phrase?”
Well, let’s go over some elementary math to help you to better understand the difference between them and to show you the level of security you have between both 12 word and 24 word seed phrases.
Can Someone Guess My Seed Phrase?
In order to understand how easy or difficult it is to guess a seed phrase, you need to first understand how many different combinations are possible.
First, let’s look at the basic parameters of a seed phrase:
- There are 2048 words that can be used to generate your seed phrase, according to BIP39 guidelines.
- Each word can be used multiple times but word reuse can reduce how random/secure your seed phrase is.
- The final word is calculated as a checksum so you can’t manually select the final word.
Most Bitcoin seed phrases are made up of either 12 or 24 of the 2048 possible seed words derived from BIP39. However, having a checksum means that we only need 11 words to generate a 12 word seed phrase, and 23 words to generate a 24 word seed phrase.
Now, let’s see how secure each one is.
12 Word Vs. 24 Word Seed Phrase Security
Once you’ve stacked your first sats, downloaded a Bitcoin wallet, and are ready to take custody of your own bitcoin, the next step is to generate your seed phrase as securely as you possibly can. When creating your seed phrase, you may ask yourself:
“How many seed words do I need…or want?”
“What’s the difference between a 12 word seed phrase and a 24 word seed phrase?”
For some, it’s a simple matter of preference or a wallet default. For others (like myself), it’s a matter of exponentially more security. Let’s dive into the basic math.
12 Word Seed Phrase Security
Based on the parameters above, we know that the number of possible combinations for a 12 word seed phrase is 2048^11.
- The first word can be 1 of 2048 words.
- The second word can be 1 of 2048 words.
- The third word can be 1 of 2048 words…and so on until 11 of 12 words are selected.
- The final word is calculated as a checksum to generate a complete 12 word seed phrase.
According to Wolfram Alpha, that’s more than 2.6 undecillion possible combinations. Until I was doing research for this article, I didn’t even know that was a number.
That means that someone would have to guess all 2.6 undecillion combinations to calculate all of the possible 12 word seed phrases in existence.
That’s obviously an enormous number of possible combinations, but what about a 24 word seed phrase?
24 Word Seed Phrase Security
Guessing a 24 word seed phrase is similar to guessing a 12 word seed phrase except there are twice as many words to guess.
One might just assume that it’s only twice as difficult to guess a 24 word seed phrase than with 12, but that couldn’t be further from the truth.
For every word added, we increase the difficulty of guessing a seed phrase by a multiple of 2048.
- So even a 13 word seed phrase would be 2048 times more difficult to guess than just 12.
- 14 words would be another 2048 times more difficult than 13.
- 15 words would be yet another 2048 times more difficult to guess than 14 words…and so on.
With 12 words + 3 more words, a 15 word seed phrase is more than 8 billion (8,589,934,592) times more difficult to guess than a 12 word seed phrase.
Now, let’s see how difficult it would be to guess a 24 word seed phrase.
Since each new word increases the difficulty of guessing a valid seed phrase by a multiple of 2048, the number of possible combinations for a 24 word seed phrase is 2048^23. Like before, it’s not 2048^24 because the final word is calculated as a checksum.
Again, until I was doing research for this article, I had never even heard of such large numbers.
You literally have better odds of winning the power ball lottery multiple times in a row than randomly guessing a 24 word seed phrase with some sats.
Technically, it’s not impossible to guess a 24 word seed phrase, but it’s so improbable that we can safely call it “practically impossible”. Meaning, it’s not possible to guess a seed phrase within the limits of a human lifespan and all of the computational power that is (currently) available to the human race.
That’s how difficult it is to guess completely unknown seed phrases — but what if you know the seed words themselves, and just need to unscramble them?
Can A Computer Guess The Order Of Scrambled Seed Words?
Let’s imagine that you bought some bitcoin back in 2015, and generated both a 12 word seed phrase and 24 word seed phrase. Then you moved some bitcoin to each wallet and stored your seed phrases somewhere safe for years. Awesome choice.
Let’s continue to imagine that you thought it would somehow protect your seed phrases from anyone who might randomly find them, so you decided to scramble your seed words because you (incorrectly) thought that it would protect your bitcoin from a potential attacker.
Please don’t ever scramble your seed phrase words. It’s just one of many ways to lose all of your Bitcoin.
Statistically, you’re far more likely to lock yourself out of your wallet forever and lose all of your bitcoin by doing something dumb like that, but it was 2015 and you thought you were a cypherpunk badass cause you’re using uncensorable money of the internet.
Then, one day in 2024, you decide to open up your wallet and see how rich you are — only to learn that you can’t remember the order of your 12 or 24 word combination. You thought you were clever, but you actually just locked yourself out of your own retirement fortune.
Now, you have two pieces of paper. One with 12 random words written on it, and 24 on the other. You know all the words themselves but you don’t know the word order. Can you guess all of the possible combinations?
Well, the answer is yes…but it’s gonna take some time. You just have to guess each possible combination.
Guess The Order Of 12 Scrambled Seed Words
In this imaginary example, let’s see how many possible combinations that you would have to systematically guess. How many possible combinations are there with just 12 words? The answer is actually pretty simple. Here’s the math.
Why is that the equation? Let’s take a closer look.
- The first word is any of the 12 random words that you have in front of you. Pick any one of them.
- The second word can now only be one of the remaining 11 words. Pick any one of those 11 for the second word.
- Now, the third guess can only be one of the remaining 10 words. Pick any one of those for the third word.
With each new word you guess, there is one less possible word that can be used for each of the following words.
So, in order to guess the order of 12 known seed words, you have to guess all 479,001,600 possible combinations. That’s less than half a billion different combinations. It probably wouldn’t take someone very long to guess with the right computer script and a decent amount of computing power.
But what about guessing the word order of your scrambled 24 word seed phrase?
Guess The Order Of 24 Scrambled Seed Words
As if scrambling 12 words wasn’t hard enough already, let’s figure out how difficult it would be to systematically guess all of the possible combinations of your 24 scrambled seed words instead of just 12.
Just like with guessing a 12 word seed phrase, you start by guessing 1 of 24 words. Once you have 1 word that you’ve guessed, you now have to guess the next word with 1 of the 23 remaining words. Then 22 words. Then 21 words, and so on until you’ve systematically guessed all 24 words.
That’s more than 620 sextillion possible combinations, which is more than one quadrillion (1,295,295,050,649,600) times the number of possible combinations with just 12 words. That’s the power of “Vires in numeris”, or “strength in numbers”, which is one of the many mantras that bitcoiners put on t-shirts, artwork, and cliché engagement tweets.
The raw level of security that you have with a 24 word seed phrase is essentially 1,295,295,050,649,600 times greater than with just 12 words.
Now, to really put this all to the test, it’s time to give away some sats.
Guess My 12 And 24 Word Seed Phrases
To show just how much more difficult it is to guess a 24 word seed phrase than a 12 word seed phrase, I am going to give away some sats to anyone who can guess my seed phrase by unscrambling the following words.
I randomly selected each word using my SeedSticks, calculated the final checksum word with my SeedSigner, and wrote down both seed phrases. I wrote the 12 words on standard paper (so I can easily destroy it once someone claims the sats), wrote the 24 word seed phrase in my Shieldfolio Stonebook (Affiliate) (because i’m not counting on anyone being able to guess my 24 word seed phrase), and then reorganized them in no particular order.
Here are 12 words that make up a valid seed phrase:
off energy lounge crisp library inmate accident occur boring aunt cherry gallery…and here’s the address that I sent 100,000 sats to: bc1ql7ka7ut3vcveydx8sy9ylhurpnc6cpy02yjrge
Here are 24 words that make up a valid seed phrase.
grab merit chuckle can island wash floor car exit mother box festival october odor camp country trial nephew coil fabric galaxy napkin appear apple…and here’s the address that I sent 1,000,000 sats to: bc1qxsd68d42agvykdueutm228uzn4s2g9qp2kk7t8
If you can guess the correct order, you can have the sats in the wallet.
The 12 word seed phrase should be pretty easy for anyone with the ability to write a script that systematically guesses all of the possible combinations. I imagine that these sats will be gone within a month. Maybe less.
UPDATE: These sats were claimed in just 25 days!
The 24 word seed phrase should be practically impossible for anyone with even large amounts of computing power. I suppose it might be easy with a quantum computer but I’m not entirely sure how accessible that is for the average human. It’s possible that it is a lot easier than I think it is, but I am willing to put my money where my mouth is to find out.
Strength In Numbers
The number of words in a seed phrase is a matter of security. They provide strength in numbers. There’s always some nuance to seed phrase security, but generally speaking, the greater the number of words that you use to generate your seed phrase, the more secure your seed phrase is.
I believe so strongly in the security of 24 word seed phrases vs just 12 that I am offering up to 1.1 million sats to anyone who can systematically guess the order of my published seed words.
Good luck.
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