Notes on bitcoin2john.py Berkeley DB dependency added to README.bitcoin

doc/README.bitcoin

@@ -1,12 +1,74 @@
 Cracking bitcoin-qt (bitcoin) wallet files with john
 ====================================================
 
-1. Run bitcoin2john.py on bitcoin wallet file(s).
+1. Run bitcoin2john.py on Bitcoin or some altcoin wallet file(s).
 
 E.g. $ ../run/bitcoin2john.py wallet.dat >> hashes
 
-2. Run john on the output of bitcoin2john.py script.
+2. Run john on the output of the bitcoin2john.py script.
 
 E.g. $ ../run/john hashes
 
 3. Wait for the password(s) to get cracked.
+
+Notes:
+
+This procedure also works with many altcoins historically forked from Bitcoin.
+
+The bitcoin2john.py script is compatible with both Python 2 and Python 3.
+
+Since Python 3 no longer provides Berkeley DB support out of the box, to get
+the script to work with Python 3 you need to install the corresponding module:
+
+pip3 install bsddb3
+
+(maybe with "sudo", depending on your setup).
+
+For the command above to work you also need to have Berkeley DB itself
+installed first, so e.g. on Fedora you need to start by running:
+
+sudo dnf install libdb-devel python3-devel
+
+The version of Berkeley DB in use by your system's Python interpreter needs to
+be compatible with the version in use by the wallet.  Unfortunately, this is
+sometimes not the case.  For example, if you receive the message "unsupported
+btree version: 10" from bitcoin2john.py, this means your altcoin wallet uses
+Berkeley DB version 6 or newer whereas your Python interpreter probably uses
+version 4 or 5 (as commonly provided by distributions for licensing reasons,
+because version 6 switched to a more restrictive license).  How to get around
+this is system-specific, but in general your options are building a suitable
+version of Berkeley DB and Python's bsddb3 from source, or moving to another
+system that might have the right versions packaged.
+
+deathmorlock and Claudio Andre provided the below instructions for Ubuntu, for
+use in a throw-away VM or container (since this messes with the system badly):
+
+sudo apt update
+sudo apt install python3 python3-pip
+
+wget https://download.oracle.com/berkeley-db/db-6.2.32.NC.tar.gz
+tar xzf db-6.2.32.NC.tar.gz
+cd db-6.2.32.NC/build_unix
+../dist/configure --prefix /usr/local/berkeley-db/6.2.32
+sudo make install
+
+# Ubuntu upstream version is bsddb3-6.2.7. So:
+YES_I_HAVE_THE_RIGHT_TO_USE_THIS_BERKELEY_DB_VERSION=1 BERKELEYDB_DIR=/usr/local/berkeley-db/6.2.32 sudo pip3 install bsddb3
+
+Alternatively to the above command, the following was also tested:
+
+sudo echo YES_I_HAVE_THE_RIGHT_TO_USE_THIS_BERKELEY_DB_VERSION=1 >> /etc/environment
+sudo echo BERKELEYDB_DIR=/usr/local/berkeley-db/6.2.32 >> /etc/environment
+
+wget https://files.pythonhosted.org/packages/fa/ad/eb82bcccbfb076b6a6797f48c339460699103065fb2a2fc72403b16970fe/bsddb3-6.2.7.tar.gz
+tar xzf bsddb3-6.2.7.tar.gz
+cd bsddb3-6.2.7
+sudo python3 setup.py install
+
+Once again, the above complicated procedure is only needed if you receive the
+"unsupported btree version: 10" error.  For regular Bitcoin wallets and many
+altcoin wallets, you would not have that error and the procedure is unneeded.
+It's only needed for some other altcoins.  Also, you should know what you're
+doing, and in particular you might need to adjust these instructions to match
+your system and the changing library versions and download locations.  These
+instructions are an example and not something that will work for you as-is.

run/bitcoin2john.py

@@ -126,6 +126,7 @@ def open_wallet(walletfile):
 
         if r is not None:
                 logging.error("Couldn't open wallet.dat/main. Try quitting Bitcoin and running this again.")
+                logging.error("See our doc/README.bitcoin for how to setup and use this script correctly.")
                 sys.exit(1)
 
         return db