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Date: Fri, 7 Dec 2018 13:07:33 +0100
From: Solar Designer <>
Subject: Re: Understand bitcoin2john script


On Sun, Dec 02, 2018 at 08:51:33PM +0100, wrote:
> I am doing some experiments with bitcoin2john on my own wallet.
> I wonder if the hash extracted by this script contains sensitive
> information, like my public btc address? Directly or indirectly.

I'm sorry no one replied to you sooner.  I was hoping someone more
directly involved with this code would.

Yes, you should assume that the "hash" contains at least semi-sensitive
information, such as your public key.  It probably does not contain
truly sensitive information, such as your private key, but I don't vouch
for this.


Need less revealing *2john "hashes" for cryptocoin wallets & encrypted archives

*2john tools should warn users when they produce particularly revealing "hashes"

Generate less revealing hashes for Bitcoin wallets

As you can see, the last one of these is a merged pull request, so that
work was completed.  I didn't review it closely, even though it was
implementation of my suggestion.  What I think we do now is take
advantage of CBC mode's properties and store only two blocks of
ciphertext, instead of the entire ciphertext.  What I think this
achieves is a slight speedup of cracking and inability to restore the
full public key from the "hash".  However, it probably doesn't help
against matching of a "hash" (through such partially-restored key, once
the passphrase is cracked) against an already known public key.  So
probably not much help for privacy.

We'd appreciate it if you (or anyone else reading this) research this
further and contribute on issues 3139 and 3140.  Note that they're not
limited to Bitcoin wallets, and the CBC mode trick should be reusable
for many other input formats to various *2john tools.

Here's someone posting a bitcoin2john "hash" (I think from prior to
issue 3290 fix?) publicly, offering a 5 BTC bounty for anyone cracking
their wallet's forgotten passphrase:


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