You’ve just received your very own Billfodl in the mail, and you go to set it up, when you realise that each slot only holds four letters. You start panicking, thinking your device is faulty as it can't possibly hold all of your recovery phrase.
Don’t worry, your Billfodl isn’t broken!
The device is designed to only hold four letters of each word, and we will explain why below.
THE BIP39 WORD LIST
The BIP39 is a mnemonic phrase - a group of easy to remember words - that serves as a backup to recover your wallet and coins in the event of your wallet becoming compromised, lost, or destroyed. This is also known as a mnemonic seed (phrase), recovery phrase, wallet backup, master seed, etc.
The BIP39 word list contains 2048 words, and your recovery phrase is made up of 12, 18, or 24 words from that list. For example, the KeepKey hardware wallet only uses 12 words. Ledger and Trezor wallets use 12/24. Other software wallets sit in the middle with 18 backups words.
You may have noticed that some of your recovery phrase words are up to eight characters long. So why does the Billfodl only let you backup four letters?
Because you only need the first four letters!
Let’s take a look at the BIP39 word list to give you a better understanding.
You will find that there are no two words with the same first four letters. All words are unique to the first four letters.
Take for example, words #27: addict and #28: address. They share the same first three letters ‘add’. But the fourth letter is different.
Out of all 2048 words, no first four letters are the same.
WHAT HAPPENS WHEN I NEED TO RESTORE MY CRYPTO WALLET?
When restoring your cryptocurrency wallet, you’ll need to select the option to “restore from recovery phrase.” You’ll then be prompted to enter your recovery phrase.
As you enter the first word, letter by letter, you will discover that the wallet will start auto-filling the rest of the word for you. For instance, if your first word is “agent”, you will input an “a” and a “g”. At this point, the wallet will likely show you “age”, “agent” and “agree”, and let you select one.
You won’t have to keep entering all of the letters in the word. All you need to enter is the first four letters before your unique word would show up as the only available option.
Because of this feature of BIP39, backing up more than the first four letters is unnecessary.
WHY NOT BACKUP ALL OF THE LETTERS ANYWAY?
There are four reasons why Billfodl do not backup the remaining words.
Cost
Backing up more letters than necessary means they would need to provide more tiles. They would also need to make the Billfodl larger.
Doing this would require more labour and raw materials. And the increased materials would make it heavier and cost more to ship. By not adding unnecessary labour and weight, they save you money.
Stability
Small contraptions like the Billfodl tend to hold up better in extreme elements, such as heat. They want the Billfodl to protect your recovery phrase in as many of these conditions as possible. The smaller they can make it the better.
Ease of Setup
More tiles mean a longer set up process. The truth is, setting up a backup is not fun. It's tedious, no matter how you slice it. They’d prefer not to make you spend any more time on it than is necessary. Especially when there is no increased benefit in doing so.
Reproducibility
There is a small possibility that backing up more letters than you need is actually bad for the backup. They have tried to engineer the Billfodl so that the lock will not open unintentionally. They cannot always predict this though.
For example, if the Billfodl is in a house fire and a heavy beam were to fall on it, the lock might break. When you go to pick it up, there is a chance the latch will come loose, and the tiles will fall out.
If this happens, you may be forced to collect the tiles and attempt to brute force the phrase using a computer. In this case, you want as little ‘noise’ in the signal as possible.
Having extra letters in your pile of tiles will only make this process more difficult. That is because it adds to the total number of different combinations possible.
If you have any other questions about why you only need four letters for a Billfodl, send us an email at support@coinstop.com.au. Or if you would like help setting up your Billfodl or hardware wallet, you can book an online consultation with us here.