How to Create a Cryptocurrency Wallet, Step by Step

What you are actually creating

A wallet does not hold coins. It holds a key, and the key authorises moving balances that live
on the network. Installing wallet software generates that key from a large random number, and
then shows you the number encoded as an ordered list of ordinary words: the recovery phrase.

That phrase is the wallet. Anyone who has it has your funds, on any device, without needing
your phone or your password. Anyone who does not have it cannot help you recover, including
the company that wrote the software. Both halves of that sentence explain every precaution
below.

1. Choose the type before the brand

   A phone or browser wallet is convenient and connected to the internet. A hardware device
   keeps the key offline and signs transactions on the device itself. For small amounts and
   learning, software is fine. For a sum you would be upset to lose, the offline option is
   the reason hardware wallets exist.

2. Download from the source, not from a search result

   Fake wallet applications are a standing problem, and paid search results are where they
   appear. Type the project’s domain in directly, or reach it from a link you already trust.
   A convincing clone that generates a phrase the attacker already knows is the whole attack.

3. Write the recovery phrase on paper, in order

   Not a screenshot, not a note application, not an email to yourself. Paper, or a metal
   backup plate if the amount justifies it. The order matters as much as the words, and one
   transposed pair produces a valid but different wallet with nothing in it.

4. Verify the backup before funding it

   Most wallets ask you to re-enter a few words. Do that honestly, from the paper rather than
   from memory. Better still, delete the wallet and restore it from the phrase before sending
   any real amount. A backup you have not tested is a hypothesis.

5. Send a small test amount first

   Then check it arrived and that you can send it back out. This catches the wrong network,
   the unsupported asset and the mistyped address while the sum is trivial, which is the only
   time those mistakes are cheap.

Where to keep the phrase

The requirements pull against each other: it has to survive fire, flood and time, and it has
to be somewhere a burglar will not find it. A single copy in one location fails the first
test. Copies in several locations fail the second. Most people settle on two copies in places
with different failure modes, which is a reasonable compromise rather than a solved problem.

Splitting the phrase across locations sounds clever and usually is not. Common schemes reduce
the security less than people assume, and every added step is another way for the recovery to fail when it is actually needed, frequently by someone else, years later, working from notes
you are no longer around to explain.

One wallet, many addresses, and why that is normal

A modern wallet generates a fresh receiving address each time you ask for one, and the old ones
keep working. The first reaction is usually that something has gone wrong, so it is worth
saying plainly that this is the intended behaviour.

All of them derive from the same recovery phrase, which is why the phrase alone restores
everything without any list of addresses. The reason for generating new ones is privacy: an
address reused across several payments links those payments to each other and to whoever knows
any one of them.

Two things follow. Funds sent to an older address still arrive and still appear in the balance,
so nothing is stranded. And a balance that looks wrong is far more often a wallet showing one
account rather than all of them than it is a missing payment.

After it exists

Two things are worth doing once the wallet is working. Learn how to check an address before
pasting it, because clipboard-hijacking malware substitutes addresses and the substitution is
designed to look similar at a glance. And learn where the network selector is, because sending
on the wrong chain is the second most common irreversible mistake after losing the phrase.

From there the wallet is infrastructure rather than a project. It needs updating occasionally
and reviewing when you grant an approval to a contract, and otherwise it should be boring. A
wallet you think about often is usually one that is holding more than it should.