Recovery story . Blockchain.info

Rebuilding a wallet from 17 remembered words

The client had part of an old Blockchain.info backup phrase — 17 words — in a format the modern site refuses to import. Recovering it took brute force and a lot of source-code archaeology and fun

Updated July 2026 · KeychainX — Wallet Recovery since 2017

Early Blockchain.info wallets used their own backup phrase, unlike the standard 12-word seed the industry later settled on. This case involved one of those legacy phrases — and a client who could only recall part of it. What made it solvable was years of studying exactly how those old wallets were built.

The situation

The client had created a Blockchain.info wallet in the early days of Bitcoin and backed it up with a word phrase — the old scheme used 15, 17, 19 or 21 words rather than the now-standard 12. Years later they remembered 17 words, but not with full confidence in the order, and the current Blockchain.com site simply would not accept the phrase. To modern software, a legacy 17-word backup looks like nothing it recognises.

What made it hard

Two problems stacked up. First, the phrase itself is non-standard — it doesn’t map onto BIP39, so off-the-shelf tools can’t restore it. Second, the client wasn’t certain of the exact word order, and word order is everything: get it wrong and the phrase reconstructs a different, empty wallet. So the task wasn’t just decoding an old format, it was finding the one correct ordering among many plausible ones.

How we cracked it — source-code archaeology

Recovering these means understanding how Blockchain.info actually turned that word list into keys at the time — a scheme that changed across the wallet’s versions and is no longer documented anywhere public. We’d reconstructed that logic by reading the wallet’s historical source code, version by version, so we could reproduce the exact derivation. From there it became a controlled brute-force problem: test the valid orderings and interpretations of the 17 known words against the client’s known address, offline, until the wallet reconstructed exactly. When the derived address matched, we knew the ordering was right beyond doubt.

The outcome

The correct arrangement rebuilt the wallet and its balance, and the client moved the funds to a modern wallet they control. As always, the fee was a percentage of the recovered value, paid only on success, and we never held the coins. A backup that the official site treated as unrecoverable was, with the right historical knowledge, entirely recoverable.

The old Blockchain.info word formats

Before the industry standardised on the 12-word BIP39 seed, Blockchain.info rolled its own backup scheme — word phrases of 15, 17, 19 or 21 words, tied to how that particular wallet version encoded its keys. Because it predates and diverges from BIP39, none of it maps onto the tools everyone uses today, which is why a perfectly valid old phrase produces nothing but errors in modern software. The encryption and encoding also shifted across the wallet’s versions, so part of any recovery is first identifying which era the phrase belongs to, then applying that version’s exact logic rather than a generic one.

Why the official site can’t help

Blockchain.com long ago dropped support for importing these legacy phrases, so their own site will tell you the phrase is invalid — which understandably leads people to assume the money is gone. It isn’t: the wallet still exists on-chain, and the keys are still derivable from the phrase if you can reproduce the original derivation. That reproduction is the whole job, and it only exists because we preserved and studied the historical code. The funds were never lost; the method to reach them had simply fallen out of the modern toolset.

What we need to try

To attempt a legacy Blockchain.info recovery we need the words you do have — however many and in whatever order you remember them — and, if at all possible, a receiving address from the wallet, because that’s what lets us confirm a rebuild is correct beyond doubt. Any sense of when the wallet was created also helps us pin down which version’s derivation logic to apply. Partial, uncertain, out-of-order — all of that is workable; a blank is not.

If you have an old Blockchain.info wallet

A lot of very early Bitcoin sits in Blockchain.info wallets whose owners tried the modern site, got an error, and concluded the coins were gone. In most of those cases the coins are still there — the phrase is real, the balance is on-chain, and only the derivation method is missing from today’s tools. The gap between “the website says invalid” and “actually recoverable” is precisely the historical knowledge of how those wallets worked. If you kept any part of an old word phrase, or the wallet ID and a password hint, don’t treat the official error message as the final word. These early wallets are some of the most rewarding to recover, and some of the most misunderstood.

What you can take from it

If you’re holding an old Blockchain.info phrase of 15 to 21 words that “doesn’t work” anymore, that’s expected — the modern site dropped support for it, but the wallet isn’t lost. Even a partial or out-of-order phrase can often be rebuilt against your address. Our Blockchain.com recovery page covers these legacy mnemonics in detail.

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