The wallet.dat file is the cornerstone of Bitcoin Core. When this file becomes corrupted or
the "BerkeleyDB" header is damaged, standard Bitcoin software will refuse to open. This guide covers how
to perform a **forensic dump** of the raw keys.
1. Understanding the BerkeleyDB Structure
Most wallet.dat files use BerkeleyDB (BDB). Inside, data is stored in "pages." A corrupted
header doesn't mean the keys are gone; it just means the index is broken. We treat the file as a raw
data stream.
2. Extracting Keys with PyWallet
The most reliable tool for non-destructive discovery is PyWallet. It bypasses the standard BDB library and reads the byte-stream directly.
git clone https://github.com/jackjack-jj/pywallet python2 pywallet.py --dumpwallet --datadir=/path/to/backup
This will output your private keys in WIF (Wallet Import Format) if the wallet is unencrypted.
3. Extracting Hashes for Hashcat
If the wallet is encrypted and you have forgotten the password, you must extract the **Master Key Hash**. We use a specialized script from the John the Ripper suite.
python3 bitcoin2john.py wallet.dat > hash.txt
The resulting hash can then be imported into Hashcat using mode 11300. On
a modern forensic cluster, we can test hundreds of thousands of password variations per second.
4. Hex-Level Forensic Carving
When the filesystem itself is corrupted (e.g., after a sudden power loss), the wallet.dat
might
be fragmented across physical sectors. In these cases, we perform **signature-based carving**. We search
for the specific BerkeleyDB page magic bytes and the ASN.1 / BER (Basic Encoding Rules) patterns
that denote a Bitcoin private key.
Private keys in a wallet.dat file are typically preceded by the hex sequence
04 20
(denoting an Octet String of 32 bytes). By scanning the raw disk image for these markers followed by
high-entropy data, we can often recover "ghost" wallets that have been deleted for months.
5. The "Midget" Attack and Key Recovery
For users who remember *most* of their password but have a few characters wrong, we employ what is known in the forensic community as a "Midget" attack (mask-based brute force). This reduces the search space from quintillions of combinations to a manageable few billion, often resulting in a successful recovery within 24-48 hours.