// learn · season 02 · episode 05
Mnemonics — your fortune in 24 words
Season 1 ended on a question: your key is an unguessable number — so where do you keep it? Season 2 — keeping the keys — is that question, answered the way custodians answer it. First step: turning the number into something a human can hold. This page runs the real BIP39 standard in your browser; nothing you generate leaves the page.
01 · the encoding
From coin flips to words
A seed phrase isn't a password someone chose. It's raw randomness — 128 or 256 bits of it — chopped into 11-bit chunks, each chunk looked up in a fixed public list of 2,048 words. Watch it happen.
your entropy — 128 coin flips
generating…
words are just numbers
The wordlist is public and standardized — 2,048 words, so each word carries exactly 11 bits (the small number on each card is the word's position in the list). The secret was never the words. It's the sequence.
⚠ the rule
This is the real BIP39 algorithm and the real wordlist — but phrases minted in a browser are for learning only. Never use a browser-generated phrase for real funds. Real wallets generate them on hardware built for the job.
02 · the safety net
The last word isn't free
Write down 24 words by hand and you will eventually mistype one. BIP39 saw that coming. Attack your own phrase and watch the validation catch it.
your phrase, under attack
✗ invalid — every word is real, but the checksum doesn't add up
The last word isn't free — part of it is a checksum, computed by hashing your entropy (episode 1's fingerprints, again). A 12-word phrase carries 4 checksum bits, a 24-word phrase 8. That's why your wallet can say “invalid phrase” when you mistype — and also why a random wrong word still sneaks through occasionally. Checksums catch typos, not thieves.
03 · back to the number
Words → the same old number
The words were never the destination. Stretched through 2,048 rounds of hashing, they become a 512-bit seed — and if you sabotaged your phrase above and haven't fixed it, watch what this panel says.
PBKDF2 · HMAC-SHA-512 · 2,048 rounds
✗ your phrase is currently broken — fix it in the panel above
A sabotaged phrase derives nothing. That's the point: the words and the wallet are the same object.
Type anything and the seed above changes completely — a different passphrase is a different wallet. Deniable and powerful… and one more thing to lose.
This 64-byte number feeds a hierarchical deterministic wallet — a tree that deterministically derives every private key and address you'll ever use, including the kind you generated, signed with, and lost in episode 4. Back up the words once, and every future key is already backed up.
04 · the paper problem
Where the words live
You've turned an unguessable number into a sentence a human can carry. Now that sentence is the treasure — and it has to live somewhere.
paper
Cheap and offline — but paper burns, floods, fades, and gets found by curious relatives. Fine to start; fragile to depend on.
steel
Stamped or engraved plates survive the house fire that destroys the paper. The standard upgrade for anything serious.
photos · cloud · notes apps
Never. A synced screenshot is a copy on machines you don't control — one breach, anywhere, ever, and the funds are silently gone.
And one more thing paper can't solve: the words outliving you is supposed to be the plan, not the accident. Who finds them, and when? The rest of season 2 is how professionals answer that — starting with removing the single piece of paper entirely.
next up
Episode 06 — Hot & cold wallets play now →The words are safe on steel. But keys that sign things have to live somewhere too — and where they live decides who can steal them.