Seed phrases can be worth alot of money these days. But there are somet things you never really consider when using or storing your seed phrases that would/could blow your tiny human mind if you really think about them. I'll go over a few of them today and hope I don't lose a reader to a freak spontaneous human combustion accident.

• The idea to use a list of regular words first came around in 2013.

It was formally adopted as a Bitcoin Improvement Proposal (BIP) called BIP-39. Before wallets used words they were simply just numbers, this is hard for us humans to write down as words are easier for us to remember. Some subsequent implementation following BIP-39 is now used by just about every wallet on every blockchain, the idea is that good for us humans.

• I already know all the words in your seed phrase 

All modern wallets that use BIP-39 use words from the same list of 2048 official seed words. There are different lists for other languages, but every wallet that uses English language is derived from this list of words.

• All words in the word list can be replaced by four letters

For example, no two words on the list start with the same four letters, so technically if you can read the first four letters you can recover the wallet. Ledger's metal seed phrase storage tube as therefore opted to only use 4 letters when storing your seed phrase, saving space and money.

• Humans suck at being random

Which is why when you create a new wallet, the software doesn't let you "choose" your seed words. Basically, you would pick words that someone (or a good computer to be more specific) could easily guess if given a few million (or billion) tries. Computers (or wallets in this case) generate a long string of random 1's, 0's which are divided into smaller 11 bit sections whic can be translated to a word in the 2048 word list that wallets use. So for example if a particular 11-bit chunk of the random sequence is “00000000101”, that is the number 5, so the 5th word in the list is used, which is “above”. When you recover a wallet using your seed phrase, the software looks up each word to find it’s position on the list and then converts that place number back to the value (i.e. if you enter “moon” it finds that word at position 1149, which in binary is 10001111101). There is however a giant design flaw with almost all wallets today, it's that they use a word list to find what actual number your seed phrase word points to. If this word list would happen to change, your recover phrase would be a fart in the wind. If you can, record what wallet and version you had so you can find the word list, or better yet, note down next to the word you wrote down it's current place in the word list used and use that to find your new recover phrase if the list were to change.

• I know the last word in your seed phrase, if you giev me the first 11

This is another level of error detection built into the mnemonic seed phrase. After that series of random 0’s and 1’s is generated, the software calculates a checksum and combines it with the last 11-bit sequence, which then determines the last word in the list. So if you know the first 11 words, you can figure out the 12th word fairly easy by trial and error.

• The same seed phrase will produce a different wallet on different blockchains

This is because a subsequent proposal, known as BIP-44, adopted in 2014, added an additional field to the seed value which identifies the coin type. This was done so that there would not be a case where the same public/private key pair existed on multiple blockchains if the user used the same word list to generate, say, separate bitcoin and ethereum wallets. Since you usually use a wallet which is designed for a particular blockchain you aren’t aware of the addition of that key value; the software just does it for you. Related to that flaw in BIP39 pointed out in #4 above, this enhancement is related to what are called derivation paths. Which is why technically, your seed phrase is not enough to recover your wallet. What I mean with this is that you should also record where your seed phrase is used, otherwise you'll never find your coins again if you run around trying different wallets.

• Some blockchains even use 24 words

Monero, for example, use 25 words (the last word includes the checksum similarly to the 12 word version). This is to increase the length of the public key/private key pair to 256/512 bits, respectively. Cardano supports either 15 or 24 word mnemonic phrases. 

• There are 5.4 Duodecillion seed phrases

That's the unit used to get the second highest 😼kitten😼 upgrade in 🍪cookie clicker🍪. To put that in perspective, there are approximately 7,500,000,000,000,000,000 grains of sand on the earth. It would be easier for you to grab a specific grain of sand than it is to guess a 12 word seed phrase. When it comes to 24 word seedphrase the number becomes insane, 2048²⁴ different combinations exist. That's around 2.9 followed by 79 numbers. The closest unit of measurment we have for that is Centillion, which is a number followed by 303 zeroes.

Short little helpful bit of advice:

Also record where and what version of software your seed phrase is used