Research . Wallet forensics

Blockchain.info legacy wallet formats, explained

Old Blockchain.info wallets are a family of formats, not one — the encryption and the backup scheme both changed over time. Knowing which version you have is the whole recovery.

Обновлено в июле 2026 года · KeychainX — Восстановление кошельков с 2017 года

Blockchain.info (now Blockchain.com) ran one of the first and most popular web wallets, and its format evolved repeatedly from 2011 onward. That history is why old wallets get stuck and why modern tools reject them. This page documents the format versions, the encryption changes, and the unusual 15–21 word backup scheme — the forensic knowledge that recovery depends on.

The format versions (v0–v3+)

A Blockchain.info wallet is an encrypted JSON blob (wallet.aes.json) protected by your password. Across versions the encryption parameters changed — principally the number of PBKDF2 iterations used to stretch the password into a key. The earliest wallets (v0) used a scheme that modern tools don’t support at all; v2–v3 standardised on higher iteration counts. Identifying the version is step one, because the wrong parameters simply won’t decrypt, even with the right password.

The hashcat modes and the v1 trap

For recovery, the encrypted blob yields a hash that password-cracking tools test against: mode 15200 covers Blockchain.info v2–v4, and early v1 uses mode 12700. There is a well-known trap here: early v1 wallets used varying iteration counts, and standard hashcat can silently fail to find a correct password on some of them — it runs, finishes, and reports nothing even when the password is in the list. If you’re certain of a v1 password and the tool finds nothing, this iteration mismatch is usually why, and it needs a customised approach.

First and second passwords

These wallets often have two secrets: a main password that unlocks the wallet and an optional second password required to spend. The second password is forgotten constantly because it’s rarely typed — you can see the balance but can’t move it. It is extracted and searched separately from the main password (its own script and hash), so identifying which one you’ve lost changes the recovery entirely.

The 15–21 word mnemonic scheme

The detail that surprises people most: before the industry settled on BIP39’s 12-word seed, Blockchain.info used its own word-phrase backup of 15, 17, 19 or 21 words. It did not encode a raw private key like BIP39 does; it encoded your Wallet ID and password. And it did not use the familiar 2,048-word list — it drew on a much larger dictionary, on the order of 50,000 words, and in some versions used two word lists (one to compute a checksum, another to encode the identifier and password). That is exactly why feeding one of these phrases into a modern BIP39 tool produces only an error: the words often aren’t even in the list the tool knows.

Как происходит восстановление

Because the earliest logic and word lists are no longer published, recovering these wallets is genuine reverse engineering: pull historical snapshots of the Blockchain.info site and its JavaScript from web archives to recover the word lists and derivation, identify which version a wallet or phrase belongs to, then reproduce that exact scheme and validate every candidate against a known address until the checksum is correct and the wallet decrypts. A partial, uncertain or out-of-order phrase is workable, because the address confirms the correct reconstruction with certainty.

Telling which era your wallet is from

The identifier and backup format usually reveal the era. A modern Wallet ID (a GUID-style code) points to the Wallet-ID era, where recovery is realistic with the ID and a password hint. The very earliest wallets, from the 2011–2012 period before Wallet IDs, used a phone number or username as the identifier and are the hardest — sometimes genuinely unrecoverable. A word-phrase backup of 15 to 21 words places you in the legacy-mnemonic scheme. Establishing the era first prevents wasted effort applying the wrong version’s logic, which is the most common reason a technically recoverable wallet gets written off.

Why the modern site returns “invalid”

Blockchain.com long ago dropped support for importing these legacy formats, so its own site tells people the phrase or wallet is invalid — which understandably leads them to assume the money is gone. It isn’t: the wallet still exists on-chain, and the keys remain derivable from the phrase or the encrypted blob if the original scheme can be reproduced. The gap between “the website says invalid” and “actually recoverable” is precisely the historical knowledge documented here — which versions used which encryption, which word lists, and which iteration counts. That knowledge only exists because it was preserved and rebuilt from archives after the fact.

Our documentation

KeychainX has reconstructed these formats and word lists from archived source across the wallet’s versions, over many client cases, because no current tool or the modern site supports them. We publish this so owners of old Blockchain.info wallets understand that an “invalid” phrase or a stuck v1 password is a solved problem, not a dead end. For the client-facing walkthrough see our Blockchain.com recovery page.

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