mmgen-wallet

mmgen = Multi-Mode GENerator

a Bitcoin cold storage solution for the command line

NOTE: For the time being, MMGen should be considered experimental software. Downloading and testing it out is easy, risk-free and encouraged. However, spending significant amounts of BTC into your mmgen-generated addresses is done at your own risk.

Features:

As with all deterministic wallets, mmgen can generate an unlimited number of address/key pairs from a single seed. You back up your wallet only once.

With MMGen you can choose from four different ways to access your Bitcoins:

1) an encrypted wallet (the AES 256 key is generated from your password using the crack-resistant scrypt hash function. The wallet's password and hash strength can be changed);

2) a short, human-readable seed file (unencrypted);

3) an Electrum-like mnemonic of 12, 18 or 24 words; or

4) a brainwallet password (recommended for expert users only).

Furthermore, these methods can all be combined. If you forget your mnemonic, for example, you can regenerate it and your keys from a stored wallet or seed. Correspondingly, a lost wallet or seed can be recovered from the mnemonic.

The wallet and seed are short, simple text files suitable for printing or even writing out by hand. Built-in checksums are used to verify they've been correctly copied. The base-58-encoded seed is short enough to memorize, providing another brain storage alternative.

Implemented as a suite of lightweight Python scripts with a command-line interface, MMGen demands practically no system resources. Yet in tandem with a bitcoind enabled for watch-only addresses (see below), it provides a complete solution for securely storing Bitcoins offline and tracking and spending them online.

Instructions for Linux/Unix:

Download/Install:

Install the ecdsa, scrypt and pycrypto modules:

        sudo pip install ecdsa scrypt pycrypto

Install mmgen:

        git clone https://github.com/mmgen/mmgen.git
        cd mmgen; sudo ./setup.py install

Install vanitygen (optional but recommended):

        git clone https://github.com/samr7/vanitygen.git
        (build and put the 'keyconv' executable in your path)

Getting Started:

On your offline computer:

Generate a wallet with a random seed:

        $ mmgen-walletgen
        ...
        Wallet saved to file '89ABCDEF-76543210[256,3].dat'

"89ABCDEF" is the Seed ID; "76543210" is the Key ID. These are randomly generated, so your IDs will naturally be different than the fictitious ones used in this example.

The Seed ID never changes and will be used to identify all keys/addresses generated by this wallet. The Key ID changes when the wallet's password or hash preset are changed.

"256" is the seed length; "3" is the scrypt hash preset. These are configurable.

Generate ten addresses with the wallet:

        $ mmgen-addrgen 89ABCDEF-76543210[256,3].dat 1-10
        ...
        Address data saved to file '89ABCDEF[1-10].addrs'

Note that the address range, "1-10", is included in the resulting filename.

        $ cat '89ABCDEF[1-10].addrs'
        89ABCDEF {
          1     16bNmyYISiptuvJG3X7MPwiiS4HYvD7ksE
          2     1AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc
          3     1HgYCsfqYzIg7LVVfDTp7gYJocJEiDAy6N
          4     14Tu3z1tiexXDonNsFIkvzqutE5E3pTK8s
          5     1PeI55vtp2bX2uKDkAAR2c6ekHNYe4Hcq7
          6     1FEqfEsSILwXPfMvVvVuUovzTaaST62Mnf
          7     1LTTzuhMqPLwQ4IGCwwugny6ZMtUQJSJ1
          8     1F9495H8EJLb54wirgZkVgI47SP7M2RQWv
          9     1JbrCyt7BdxRE9GX1N7GiEct8UnIjPmpYd
          10    1H7vVTk4ejUbQXw45I6g5qvPBSe9bsjDqh
        }

To store your Bitcoins, spend them into these addresses from whatever wallets/software you're currently using. If you have lots of BTC, generate many addresses so that each address will have only a relatively small balance.

Spending your stored coins:

Take address 1 out of cold storage by generating a key for it:

        $ mmgen-keygen 89ABCDEF-76543210[256,3].dat 1
        ...
        Key data saved to file '89ABCDEF[1].akeys'

        $ cat 89ABCDEF[1].akeys
        89ABCDEF {
          1  sec:  5JCAfK1pjRoJgmpmd2HEMNwHxAzprGIXeQt8dz5qt3iLvU2KCbS
             addr: 16bNmyYISiptuvJG3X7MPwiiS4HYvD7ksE
        }

Save the .akeys file to a USB stick and transfer it to your online computer.

On your online computer, import the secret key into a running bitcoind or bitcoin-qt:

        $ bitcoind importprivkey 5JCAfK1pjRoJgmpmd2HEMNwHxAzprGIXeQt8dz5qt3iLvU2KCbS

You're done! This address' balance can now be spent.

OPTIONAL: To track balances without exposing secret keys on your online computer, download and compile sipa's bitcoind patched for watch-only addresses:

        $ git clone https://github.com/sipa/bitcoin
        $ git branch mywatchonly remotes/origin/watchonly
        $ git checkout mywatchonly
        (build, install)
        (You may have to install libboost-all-dev for the build to succeed)

With your newly-compiled bitcoind running, import the addresses from '89ABCDEF[1-10].addrs' to track their balances:

        $ bitcoind importaddress 16bNmyYISiptuvJG3X7MPwiiS4HYvD7ksE
        $ bitcoind importaddress 1AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc
        $ ...

Using the mnemonic and seed features:

Continuing our example above,

Generate a mnemonic from the wallet:

        $ mmgen-walletchk -m '89ABCDEF-76543210[256,3].dat'
        ...
        Mnemonic data saved to file '89ABCDEF.words'

        $ cat 89ABCDEF.words
        pleasure tumble spider laughter many stumble secret bother
        after search float absent path strong curtain savior
        worst suspend bright touch away dirty measure thorn

Note: a 128- or 192-bit seed will generate a shorter mnemonic of 12 or 18 words. You may generate a wallet with a these seed lengths by using the -l option of mmgen-walletgen. Whether you consider 128 bits of entropy enough is your call. It's probably adequate for the foreseeable future.

Generate addresses 1-11 using the mnemonic instead of the wallet:

        $ mmgen-addrgen -m 89ABCDEF.words 1-11
        ...
        Address data saved to file '89ABCDEF[1-11].addrs'

Compare the first ten addresses with those earlier generated from the wallet. You'll see they're the same.

Recover a lost wallet using the mnemonic:

        $ mmgen-walletgen -m 89ABCDEF.words
        ...
        Wallet saved to file '89ABCDEF-01234567[256,3].dat'

Note that the regenerated wallet has a different Key ID but of course the same Seed ID.

Seeds are generated and input the same way as mnemonics. Just change the -m option to -s in the preceding commands.

A seed file for a 256-bit seed looks like this:

        $ cat 8B7392ED.mmseed
        f4c84b C5ZT wWpT Jsoi wRVw 2dm9 Aftd WLb8 FggQ eC8h Szjd da9L

And for a 128-bit seed:

        $ cat 8E0DFB78.mmseed
        0fe02f XnyC NfPH piuW dQ2d nM47 VU

The latter is short enough to be memorized or written down.

The first word in the seed file is a checksum. To check that you've written or memorized the seed correctly (should you choose to do so), compare it with the first 6 characters of a sha256 hash of the remainder of the line (with spaces removed).

Mnemonics and seeds — additional information:

Mnemonic and seed data may be entered at a prompt instead of from a file. Just omit the filename on the command line.

Mnemonic and seed data may be printed to standard output instead of a file using the -S option of mmgen-walletchk.

Mnemonic and seed files may be output to a directory of your choice using the -d option of mmgen-walletchk.

Bear in mind that mnemonic and seed data is unencrypted. If it's compromised, your Bitcoins can easily be stolen. Make sure no one's looking over your shoulder when you print mnemonic or seed data to screen. Securely delete your mnemonic and seed files. In Linux, you can achieve additional security by writing the files to volatile memory in '/dev/shm' instead of disk.

Vanitygen note:

When available, the 'keyconv' utility from the vanitygen package is used to generate addresses as it's much faster than the Python ecdsa library.

Test suite:

To see what tests are available, run the scripts in the 'tests' directory with no arguments. Among others, you might find the following tests to be of interest:

Compare 10 addresses generated by 'keyconv' with mmgen's internally-generated ones:

tests/bitcoin.py keyconv_compare_randloop 10

Convert a string to base 58 and back:

tests/bitcoin.py strtob58 'a string'

Convert a hex number to base 58 and back:

tests/bitcoin.py hextob58 deadbeef

Perform 1000 hex -> base58 -> hex conversions, comparing results stringwise:

tests/bitcoin.py hextob58_pad_randloop 1000

Generate a 12-word mnemonic from a random 128-bit seed:

tests/mnemonic.py random128

or an 18-word mnemonic from a random 192-bit seed:

tests/mnemonic.py random192

or a 24-word mnemonic from a random 256-bit seed:

tests/mnemonic.py random256