Why Are Four-letter Words the Standard for Recovery Seed Backup?

Cryptosteel - a Paradigm of Hardware Wallet BackupsSecure offline storage of your private key is one of the foundations of self-custodianship. Welcome to the world of Cryptosteel products: the Cassette and Capsule are designed as easy-to-use offline backup devices, ready to be assembled in minutes straight out of the box.

Cryptosteel – a Paradigm of Hardware Wallet Backups

Nonetheless, if you get stuck – we’re here to help. The following article is about one of the most commonly asked questions we receive at Cryptosteel Customer Support.

The most popular method of gathering and holding on to cryptocurrency resources is through a hardware wallet device – our products are designed to safeguard your recovery phrase seed words so you can rest assured your assets are in practically no danger at all. The mnemonic phrase stored in a Cryptosteel Cassette or Capsule lets the blockchain system uniquely identify your resources and accesses them via the most popular compatible wallet types like Trezor, Ledger, and Blockstream. Our products are tested to make sure seed phrases work easily – entered and read back. Software wallet safety is best complimented by a permanent offline recovery phrase facilitating measure!

You’ve just received your Cryptosteel in the mail, and as you prepare to set it up you realize that your seed phrase won’t fit the device unless you use words with four letters. “OH NO!” you think. “Something’s wrong!! Why doesn’t my entire seed phrase fit?”

Don’t worry. There’s nothing wrong with your Cryptosteel. It isn’t too short, all is as it should be, by design. 

There’s a very good reason the Cryptosteel only holds four letters of each word, and that’s what we’re here to explain. :)

BIP39 Words

A mnemonic keyphrase is a unique random seed value used to generate the whole structure of the private keys in a deterministic wallet. In other words, having the master seed value allows accessing your bitcoins or other cryptocurrencies. It’s easier to process than a string of random signs, but still provides a high level of security. The standard for generating mnemonic keyphrases is BIP39 (Bitcoin Improvement Proposal).

The BIP39 Word List is a collection of words. A cryptocurrency recovery phrase (or seed phrase) is made up of twelve, eighteen, or twenty-four words drawn from the BIP39 word list. There are 2048 words in this word collection. They are supported by the majority of popular software wallets.

The first four letters in this list are unique to each word in the wordlist. To put it another way, no two words in this list have the same first four characters. If you know the first four letters, you will know the remainder. 

There is no fourth letter in words with only three letters. There are no more letters following the word “add” so it must be the word “add”.

Although the word “addict” appears in the BIP39 wordlist, you substitute “addi” for “addict”

Three-letter words are the shortest in the BIP39 list, amounting to around 30, while the longest words consist of eight letters. More than the first four letters do not need to be backed up because of this feature of BIP39.

Cryptosteel Cassette can be used for twelve-word and twenty-four-word abbreviated seeds.


The Cryptosteel Capsule set includes tiles with all printable ASCII characters for storing your private key and contains separators – parts used to mark where one word ends and the next starts.

The Cryptosteel Cassette has A-Z letters and blank tiles ▯ for three-letter words. 

The Cassette has slots for inserting 24 abbreviated mnemonic words – if the word is shorter than four letters, use a blank tile ▯.

Here are examples – | signifies a separator and ▯ signifies a blank tile.

Twelve-word seed phrase 

metal spatial guide excuse wheat fly sun mind picture sadness undo update

Storage – Cryptosteel Capsule

meta | spat | guid | excu | whea | fly | sun | mind | pict | sadn | undo | upda

| signifies a separator


metal | spatial | guide | excuse | wheat | fly | sun | mind | picture | sadness | undo | update

| signifies a separator

Storage – Cryptosteel Cassette

meta spat guid excu whea fly▯ sun▯ mind pict sadn undo upda

signifies a blank tile

Eighteen-word seed phrase

jewel chicken artefact harsh mixed clinic job spot casual sibling lens stock copper possible wait like width few

Storage – Cryptosteel Capsule

jewe | chic | arte | hars | mixe | clin | job | spot | casu | sibl | lens | stoc | copp | poss | wait | like | widt | few

| signifies a separator

Storage – Cryptosteel Cassette

jewe chic arte hars mixe clin job▯ spot casu sibl lens stoc copp poss wait like widt few▯

signifies a blank tile

Twenty-four-word seed phrase

magic mushroom impose peanut theme turkey next swing sausage slab borrow coffee expire dad broken garage poverty unlock quarter income option target fringe term

 Storage – Cryptosteel Capsule

magi | mush | impo | pean | them | turk | next | swin | saus | slab | borr | coff | expi | dad | brok | gara | pove | unlo | quar | inco | opti | targ | frin | term |

| signifies a separator

Storage – Cryptosteel Cassette

magi mush impo pean them turk next swin saus slab borr coff expi dad▯ brok gara pove unlo quar inco opti targ frin term 

signifies a blank tile

Crypto Wallet Recovery

Hardware wallets have the option to recover the private keys of your wallet using the backed-up seed phrase. This option is used in cases like software updates or wallet swapping. You’ll be prompted to enter your recovery phrase. 

As you type the initial letter of the word, you’ll see that the wallet begins to autofill the rest of the word for you. For example, if your first word is “vacant”, you’ll type “v” and “a”. At this stage, the wallet will most likely display the words “vacant” and “vacuum” for you to choose from. 

You won’t have to choose letters over and over again. The wallet is attempting to facilitate your data retrieval.

Let’s use the word “zoo” as an example once more. Because “zoo” is the only word in the BIP39 “z” List that starts with a “oo”  will most likely force you to choose it as soon as you type the letters “zo”

Full Words – Why Not?

Simplicity is the highest form of sophistication – hence we try to simplify the backup process using abbreviated versions of the words in our seed phrase. Most wallets provide hints to make entering the words easier. It’s simply not necessary to write down the full ones. On a more practical note – size matters, and we think the dimensions of the Cassette and Capsule are perfectly balanced. Thirdly, setup time is minimal. A larger number of tiles requires more minutes to combine in a sequence. 

Creating a backup requires patience and is a task that requires focus. No need for you to spend any more time than is absolutely required on it, especially if there’s no actual benefit and storing more than four letters is simply redundant.

Twelve Words – What Then?

If you really want to, you can use full words – but only if your BIP39 seed phrase consists of 12 words. Check out the diagram above for a recommended workflow. Why is it possible? As mentioned, the longest word on the BIP39 list has 8 characters. 

12 x 8 + 11 separators = 117 < 123 max. limit for the Capsule.

The Bottom Line

Mnemonic seed phrases that use the BIP39 standard were designed to be abbreviated to their first four letters. The Cryptosteel Cassette and Cryptosteel Capsule are compatible with all software and hardware wallets supporting BIP39 seed phrases. While the Cryptosteel Cassette can be used for twelve-word and twenty-four-word abbreviated seeds, the Cryptosteel Capsule is more universal. It provides space for up 123 tiles, which can be organized as up to 24 abbreviated 4 character words divided by separators, or 12 full-length mnemonic words with separators. 

Shamir Backup – Multiple Capsules for Higher Security

It’s possible to achieve even greater protection of your seed phrase by splitting it into multiple capsules using the Shamir Backup system, allowing dispersed storage and heightened security. Check out this article to find out more.

In Case You Still Have Questions

Cryptosteel has lots of helpful resources to support you in your journey to decentralizing your assets! Check out our YouTube channel for tutorials, product demos, and explainer videos. We also have many fantastic blog articles on our website about our products and philosophy. Send us an email at [email protected] if you have any further queries regarding a Cryptosteel product or if you’re curious about something else. We’d be delighted to help!