Pandemic project: A cheap and secure metal seed phrase storage
https://ift.tt/3qseWsQ
**TL/DR:** Got into bitcoin, needed a safe way to store my seed phrase, ended up bootstrapping a product: easy, affordable & secure stainless steel seed phrase storage.
# Background:
I got into crypto a year ago, initially through working with Bitcoin in anti money laundering. After buying a Ledger I asked r/Bitcoin for ideas about how to store a seed phrase safely.
Stamping or engraving letters on metal seemed like the go to solution, but not having lots of tools or a workshop, I would have preferred a toolless approach. Also stamping stainless steel is actually not the easiest task.
Nice seed phrase storage products do exist, but since a Ledger was $59, I did not want to spend $100 or more on an indestructible bulky steel seed phrase storage, like a Hodler Swiss. And even the simplest steel storage sets you back around $20 for the stamping set and materials.
So what became my pandemic project was building a seed phrase storage that would be:
1. Easy to fill,
2. Affordable, and
3. Safe.
# Seed storage design:
First I thought of using something like titanium, but stainless steel will really be enough for most of your usual threat vectors. And even unobtainium won’t help if you lose access to the location of your seed storage. So if you want to play it **really safe**, I learned that [secret sharing](https://ift.tt/3FHHqoX) is the way to go.
You go with what you know – having some background in designing sheet metal products, a number of design iterations resulted in credit **card sized stainless steel cards or tags**.
[Credit card sized stainless steel cards.](https://ift.tt/349Jk3V)
Toolless writing on stainless steel was the tricky part – I ended up choosing removing perforated sections of material to indicate letters. And additionally, a simple encoding that allows writing a letter by removing only one or two sections. This kept the size small and the effort needed to write at a minimum.
[Removing material to indicate letters.](https://ift.tt/3zaHKtR)
# Encoding letters:
One simple solution would be to use digital letter shapes to indicate letters, as in old school digital alarm clocks, but using them would require quite a lot of effort to write 24 words, 4 letters each, in total 96 letters. Each digital letter would require removing up to 7 sections to indicate one letter, which would be a lot of work.
The words used in seed phrases come from a specific [list of 2048 words](https://ift.tt/1Amc5Ar). The word list is created so that **it is enough to type the first four letters** to unambiguously identify each word ([BIP 39](https://ift.tt/3sJZY4b).
I chose encoding each letter with an 8-bit binary array, so basically a byte (0, 0, 0, 0, 0, 0, 0, 0), or actually:
0 0 0 0
0 0 0 0
You could encode the words basically as you wish, either with [alphabets in binary](https://ift.tt/3ELkmEM), or using a simple encoding that allows writing letters A-Z by removing only one or two sections per letter. This encoding logically follows alphabets, in that 1st letter, A, is:
1 0 0 0
0 0 0 0
2nd letter, B, is:
0 1 0 0
0 0 0 0
9th letter, I, is:
1 1 0 0
0 0 0 0
10th letter, J, is:
1 0 1 0
0 0 0 0
And so on. So for example HODL would be:
0 0 0 0 1 0 0 0 0 0 0 1 1 0 0 0
0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0
(H) (O) (D) (L)
And so on.
One tag has four words, so a set of 6 tags allows storing 24 words. Each tag also contains a section indicating the sequence of the tags – 1st, 2nd, etc. This means, for example, that the 1st word of the 2nd tag is the 5th word in your seed phrase.
One set for storing 24 words includes then 6 tags for writing and a legend tag to help with encoding the letters.
[A legend tag with the encoding key.](https://ift.tt/32Fcyai)
# Pros & cons:
This design ticks all my boxes:
* Easy to fill without tools
* Small, which means easy to hide (+ allows offering free shipping for the product)
* Affordable ($20-$30 per set)
* No need for manufacturing or storing loose letters, as in many solutions
* No need for disclosing your seed phrase to 3rd parties, as would be needed in custom laser cutting
* Allows splitting to several locations (or **secret sharing**).
That said, this is still not an ideal solution, since an encoding step is needed. An *ideal* solution would be owning a laser cutter and cutting and engraving your own steel tags without 3rd parties – but at least for me, this is an acceptable compromise, given the affordable price point.
And although for example a thick plate of titanium would be closer to being indestructible than thinner stainless steel tags, the possibility for secret sharing makes this method of storing one of the safest solutions out there.
[One set of six tags + a legend tag.](https://ift.tt/3pBb61y)
# Conclusion:
Having done products and startups before, naming is always difficult, especially if you want a .com-domain. Since the design resembles dog tags, **Seedtags** seemed fitting, and luckily [seedtags.com](https://seedtags.com/) was up for grabs!
After focusing solely on digital products during the last few years, working on a physical product has been really nice for a change. Any feedback, improvement ideas or thoughts on the design are highly appreciated!
I’m also building a web store @ [seedtags.com](https://seedtags.com/) to test the waters if also other people might have a similar need – let me know what you think!✌🏼
Cryptocurrency
