Getting-Started-with-MMGen-Wallet.md

Before you begin, note that the filenames, seed IDs and Bitcoin addresses used in this primer are intentionally invalid and are for purposes of illustration only. As you perform the exercises, you will substitute real ones in their place.

The up arrow (for repeating commands) and tab key (or Ctrl-I) (for completing commands and filenames) will speed up your work at the command line greatly.

The examples in this tutorial are geared towards Bitcoin, but with some modification they may be used with altcoins and forkcoins for which MMGen Wallet supports transaction operations (BCH, LTC, ETH, ETC and XMR as of this writing). See Altcoin-and-Forkcoin-Support for more details.

Invocation

MMGen Wallet is not a single program but a suite of lightweight scripts run from the command line. Commands all begin, not surprisingly, with mmgen, and thus you may view all available commands by typing mmgen followed by the TAB key. Every command has a help screen displaying detailed usage and options information. To view it, type the command name followed by --help. Note that most command options have long and short versions. For example, the --help option may be abbreviated to -h. Exceptions are the options listed by --longhelp, which have no short versions.

MMGen Wallet’s commands are generally interactive, providing you with information and prompting you for input. The --verbose or -v option requests commands to be more wordy, while the --quiet or -q option suppresses all but the most essential information. These options are available for all MMGen Wallet commands. The --yes option (available only for certain commands) suppresses even more information and can be used to make some commands non-interactive and scriptable.

Certain options require parameters, such as the --seed-len option, for instance, which takes a parameter of 128, 192 or 256. Commands may also take optional or required arguments. For example, mmgen-addrgen requires an address or range of addresses as an argument. Arguments must always follow options on the command line.

Sample command invocations:

$ mmgen-txcreate --help
$ mmgen-addrgen --verbose 1-10
$ mmgen-walletgen
$ mmgen-walletgen --quiet --seed-len 128

Configuration file

Just like Bitcoin Core, MMGen Wallet has its own data directory and configuration file. The data directory is .mmgen in the user’s home directory and the config file is mmgen.cfg. The config file contains global settings which you may wish to edit at some point to customize your installation. These settings include the maximum transaction fee; the user name, password and hostname used for communicating with your Bitcoin or altcoin daemon; and a number of others.

Bob and Alice regtest mode

If you just want to quickly test using MMGen Wallet, it’s possible to perform all wallet generation, wallet format conversion, address and key generation, and address import operations on an offline computer with no blockchain and no bitcoin balance.

If you want to practice creating, signing and sending transactions with real bitcoins, however, you’ll need a fully synced blockchain and some coins to play with. This involves an expenditure of both time and money.

Fortunately, there’s an alternative: MMGen Wallet’s regtest mode creates a virtual network of two users, Bob and Alice, who transact with each other on a private blockchain. All of MMGen Wallet’s functionality is available in regtest mode, making it an ideal way to learn to use the wallet without risking real coins. You may wish to pause here and perform the steps in the tutorial MMGen Wallet Quick Start with Regtest Mode before continuing on.

Generating a Wallet

NOTE: MMGen Wallet supports a “default wallet” feature. After generating your wallet, you’ll be prompted to make it your default. If you answer ‘y’, the wallet will be stored in your MMGen data directory and used for all future commands that require a wallet or other seed source.

You may not want this feature if you plan to store your wallet in a location other than your MMGen data directory. Otherwise, it’s recommended, as it frees you from having to type your wallet filename on the command line.

The following examples assume that you’ve chosen to use a default wallet. If you haven’t, then you must include the path to a wallet file or other seed source in all commands where a seed source is required.

On your offline computer, generate a wallet:

$ mmgen-walletgen
...
MMGen wallet written to file '/home/username/.mmgen/89ABCDEF-76543210[256,3].mmdat'

89ABCDEF is the Seed ID; 76543210 is the Key ID. These are randomly generated, so your IDs will of course be different than these.

The Seed ID never changes and is used to identify all keys/addresses generated by this wallet. Since it’s your wallet’s primary identifier, you should memorize it visually. The Key ID changes whenever the wallet’s password or hash preset are changed and doesn’t need to be memorized.

256 is the seed length; 3 is the scrypt hash preset. These values are configurable: type mmgen-walletgen --help for details.

Before transferring funds into your wallet, you should back it up in several places and preferably on several media such as paper, flash memory or optical disk. You’re advised to use a passphrase with your wallet. Otherwise, anyone who gains physical access to one of your backups can easily steal your coins. Don’t forget your passphrase. If you do, the coins in your wallet are gone forever.

Since the wallet is a small, humanly readable ASCII file, it can easily be printed out on paper.

Another highly recommended way to back up your wallet is to generate a mnemonic seed phrase or seed file as described below and write it down or memorize it. If you have an average or better memory, you’ll find memorizing your seed phrase to be surprisingly easy. And the peace of mind that comes with knowing that your coins are recoverable even if you lose all your physical backups can’t be overestimated.

Transacting

The following transacting information is applicable to BTC, BCH, LTC, ETH and ETC. For transacting with Monero, consult Altcoin-and-Forkcoin-Support and the mmgen-xmrwallet help screen.

Generate addresses (offline computer)

Now generate ten Segwit-P2SH addresses with your just-created wallet:

$ mmgen-addrgen --type=segwit 1-10
...
Addresses written to file '89ABCDEF-S[1-10].addrs'

$ cat '89ABCDEF-S[1-10].addrs'
89ABCDEF SEGWIT {
  1    36bNmyYISiptuvJG3X7MPwiiS4HYvD7ksE
  2    3AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc
  3    3HgYCsfqYzIg7LVVfDTp7gYJocJEiDAy6N
  4    34Tu3z1tiexXDonNsFIkvzqutE5E3pTK8s
  5    3PeI55vtp2bX2uKDkAAR2c6ekHNYe4Hcq7
  6    3FEqfEsSILwXPfMvVvVuUovzTaaST62Mnf
  7    3LTTzuhMqPLwQ4IGCwwugny6ZMtUQJSJ1
  8    3F9495H8EJLb54wirgZkVgI47SP7M2RQWv
  9    3JbrCyt7BdxRE9GX1N7GiEct8UnIjPmpYd
  10   3H7vVTk4ejUbQXw45I6g5qvPBSe9bsjDqh
}

Note that the address range 1-10 specified on the command line is included in the resulting filename.

MMGen Wallet currently supports four address types for Bitcoin and Bitcoin code fork coins: legacy (uncompressed P2PKH), compressed (compressed P2PKH), segwit (P2SH-P2WPKH) and bech32 (native Segwit), denoted by the code letters L, C, S and B respectively. Address types can be referred to either in full or by code letter. To generate Bech32 addresses, for example, you can specify either --type=bech32 or --type=B on the command line.

For backwards compatibility, legacy addresses with uncompressed public keys are generated by default, but this is almost certainly not what you want unless you’re restoring an old MMGen Wallet installation created before compressed address support was added. Most new users will wish to generate either Segwit-P2SH (S) or Bech32 (B) addresses instead. For BCH, which lacks Segwit support, compressed (C) addresses are the best choice.

Generation examples for various address types:

# legacy (uncompressed P2PKH)
$ mmgen-addrgen 1-10
...

$ cat '89ABCDEF[1-10].addrs'
89ABCDEF {
  1   12GiSWo9zIQgkCmjAaLIrbPwXhKry2jHhj
...

# compressed P2PKH
$ mmgen-addrgen --type=compressed 1-10
...

$ cat '89ABCDEF-C[1-10].addrs'
89ABCDEF COMPRESSED {
  1   13jbRxWjswXtaDzLBJDboMcIe6nLohFb9M
...

# Bech32 (native Segwit)
$ mmgen-addrgen --type=bech32 1-10
...

$ cat '89ABCDEF-B[1-10].addrs'
89ABCDEF BECH32 {
  1   bc1q9c9273thh3xh86lk6z34raejz6j2s8ytgyb7my
...

Note that for non-legacy address types the code letter is included in the filename.

To fund your wallet, first import the addresses into your tracking wallet and then send some coins to any of them. If you run out of addresses, generate more. To generate a hundred addresses you’d specify an address range of 1-100.

Let’s say you’ve decided to spend some BTC into the first four addresses above. Begin by importing these addresses into the tracking wallet on your online machine so their balances will be visible. For convenience of reference, provide the addresses with labels. We’ll use the labels ‘Donations’, ‘Storage 1’, ‘Storage 2’ and ‘Storage 3’.

Make a copy of the address file

$ cp '89ABCDEF-S[1-10].addrs' my.addrs

and edit it using the text editor of your choice,

$ nano my.addrs

adding labels to the addresses you’ve chosen to spend to:

# My first MMGen addresses
89ABCDEF SEGWIT {
  1    36bNmyYISiptuvJG3X7MPwiiS4HYvD7ksE  Donations
  2    3AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc  Storage 1
  3    3HgYCsfqYzIg7LVVfDTp7gYJocJEiDAy6N  Storage 2
  4    34Tu3z1tiexXDonNsFIkvzqutE5E3pTK8s  Storage 3
  5    3PeI55vtp2bX2uKDkAAR2c6ekHNYe4Hcq7
  6    3FEqfEsSILwXPfMvVvVuUovzTaaST62Mnf
  7    3LTTzuhMqPLwQ4IGCwwugny6ZMtUQJSJ1
  8    3F9495H8EJLb54wirgZkVgI47SP7M2RQWv
  9    3JbrCyt7BdxRE9GX1N7GiEct8UnIjPmpYd
  10   3H7vVTk4ejUbQXw45I6g5qvPBSe9bsjDqh
}

Any line beginning with # is a comment. Comments may be placed at the ends of lines as well.

Save the file, copy it onto a USB stick and transfer it to your online computer.

Import addresses (online computer)

Start the coin daemon with the required options (see the Install-Bitcoind wiki page for more details on invoking the daemon for your coin and platform).

Upon startup, older daemons used to automatically generate a new default wallet.dat, which MMGen Wallet used as its tracking wallet. With newer daemons (e.g. Core 0.21.0 and above), the tracking wallet will be a directory named mmgen-tracking-wallet, located by default under the wallets subdirectory in your daemon’s datadir.

Import the ten addresses into your new tracking wallet with the command:

$ mmgen-addrimport --batch my.addrs

These addresses will now be tracked: any BTC transferred to them will show up in your listing of address balances. Balances can be viewed using mmgen-tool listaddresses (the showempty option requests addresses with empty balances to be displayed too).

$ mmgen-tool listaddresses showempty=1
MMGenID       ADDRESS                             COMMENT    BALANCE
89ABCDEF:S:1  36bNmyYISiptuvJG3X7MPwiiS4HYvD7ksE  Donations    0
89ABCDEF:S:2  3AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc  Storage 1    0
89ABCDEF:S:3  3HgYCsfqYzIg7LVVfDTp7gYJocJEiDAy6N  Storage 2    0
89ABCDEF:S:4  34Tu3z1tiexXDonNsFIkvzqutE5E3pTK8s  Storage 3    0
89ABCDEF:S:5  3PeI55vtp2bX2uKDkAAR2c6ekHNYe4Hcq7               0
...
TOTAL: 0 BTC

While not covered in this introduction, note that it’s also possible to import external coin addresses into your tracking wallet. This allows MMGen Wallet to track and spend funds from another wallet without having to transfer the coins through the network. To do this, you must save the keys corresponding to the given addresses in a separate file for use during transaction signing.

Note that each address has a unique ID (the ‘MMGen ID’) consisting of a Seed ID, address type code letter, and index. Addresses of different types may be imported into the same tracking wallet, and since they’re generated from different sub-seeds you needn’t worry about key reuse. For example, the addresses 89ABCDEF:S:1 and 89ABCDEF:B:1 are cryptographically unrelated: no one but the wallet’s owner can see that they were generated from the same seed.

Now that your addresses are being tracked, you may go ahead and send some BTC to them over the Bitcoin network. If you send 0.1, 0.2, 0.3 and 0.4 BTC respectively, your address listing will look like this after the transactions have confirmed:

$ mmgen-tool listaddresses
MMGenID       COMMENT    BALANCE
89ABCDEF:S:1  Donations    0.1
89ABCDEF:S:2  Storage 1    0.2
89ABCDEF:S:3  Storage 2    0.3
89ABCDEF:S:4  Storage 3    0.4
TOTAL: 1 BTC

Create a transaction (online computer)

Now that you have some BTC under MMGen Wallets’s control, you’re ready to create a transaction. Note that transactions are harmless until they’re signed and broadcast to the network, so feel free to experiment and create transactions with different combinations of inputs and outputs. Of course, if you’re using testnet or regtest mode, then you risk nothing even when broadcasting transactions.

To send 0.1 BTC to the a third-party address 3AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc, for example, and send the change back to yourself at address 89ABCDEF:S:5, you’d issue the following command:

$ mmgen-txcreate 3AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc,0.1 89ABCDEF:S:5

mmgen-txcreate accepts either MMGen IDs or Bitcoin addresses as arguments.

NOTE: For backwards compatibility, legacy addresses may omit the code letter from the MMGen ID. Thus address 89ABCDEF:L:5 may be expressed as 89ABCDEF:5. For other address types the code letter is mandatory.

To send 0.1 BTC to each of addresses 89ABCDEF:S:6 and 89ABCDEF:S:7, sending the change to 89ABCDEF:S:8, you’d do this:

$ mmgen-txcreate 89ABCDEF:S:6,0.1 89ABCDEF:S:7,0.1 89ABCDEF:S:8

As you can see, each address is followed by a comma and an amount, except for the change address, for which the amount will be calculated automatically. All addresses belonging to your seed in the above examples are already imported and tracked, so you’re OK. If you wanted to send to 89ABCDEF:S:11, you’d have to import it first.

Let’s go with the first of our two examples above.

Upon invocation, the mmgen-txcreate command shows you a list of your unspent outputs along with a menu allowing you to sort the outputs by four criteria: transaction ID, address, amount and transaction age. Your overall balance in BTC appears at the top of the screen. In our example, the display will look something like this:

UNSPENT OUTPUTS (sort order: Age)  Total BTC: 1
 Num  TX id  Vout    Address                               Amt(BTC) Age(d)
 1)   e9742b16... 5  3L3kxmi.. 89ABCDEF:S:1    Donations       0.1    1
 2)   fa84d709... 6  3N4dSGj.. 89ABCDEF:S:2    Storage 1       0.2    1
 3)   8dde8ef5... 6  3M1fVDc.. 89ABCDEF:S:3    Storage 2       0.3    1
 4)   c76874c7... 0  3E8MFoC.. 89ABCDEF:S:4    Storage 3       0.4    1

Sort options: [t]xid, [a]mount, a[d]dress, [A]ge, [r]everse, [M]mgen addr
Display options: show [D]ays, [g]roup, show [m]mgen addr, r[e]draw screen
'q'=quit view, 'p'=print to file, 'v'=pager view, 'w'=wide view, 'l'=add label:

After quitting the menu with ‘q’, you’ll see the following prompt:

Enter a range or space-separated list of outputs to spend:

Here you must choose unspent outputs of sufficient value to cover the send amount of 0.1 BTC, plus the transaction fee (for more on fees, see ‘Transaction Fees’ under ‘Advanced Topics’ below). Output #2 is worth 0.2 BTC, which is sufficient, so we’ll choose that and hit ENTER. When prompted for a transaction fee, we’ll choose 0.0001 BTC (note that integer fees followed by the letter ‘s’ for “satoshis per byte” are also permissible). After a couple more prompts and confirmations, your transaction will be saved:

Transaction written to file 'FEDCBA[0.1].rawtx'

The transaction filename consists of a unique MMGen Transaction ID plus the non-change spend amount.

As you can see, MMGen Wallet gives you complete control over your transaction inputs and change addresses. This feature will be appreciated by privacy-conscious users.

Sign a transaction (offline computer)

Now transfer the the raw transaction file to your offline computer and sign it using your default wallet:

$ mmgen-txsign FEDCBA[0.1].rawtx
...
Signed transaction written to file 'FEDCBA[0.1].sigtx'

Note that the signed transaction file has a new extension, .sigtx.

Send a transaction (online computer)

Now you’re ready for the final step: broadcasting the transaction to the network. Start bitcoind if it’s not already running, and make sure your blockchain is fully synced. Then copy the signed transaction file to your online computer and issue the command:

$ mmgen-txsend FEDCBA[0.1].sigtx
...
Transaction sent: abcd1234....

Like all MMGen Wallet commands, mmgen-txsend is interactive, so you’ll be prompted before the transaction is actually broadcast. If the send was successful, a 64-character hexadecimal Bitcoin Transaction ID will be displayed (abcd1234... in our case).

Once the transaction is broadcast to the network and confirmed, your address listing should look something like this:

$ mmgen-tool listaddresses minconf=1
MMGenID       COMMENT    BALANCE
89ABCDEF:S:1  Donations    0.1
89ABCDEF:S:3  Storage 2    0.3
89ABCDEF:S:4  Storage 3    0.4
89ABCDEF:S:5               0.0999
TOTAL: 0.8999 BTC

Alternatively, you may use mmgen-tool twview or mmgen-txcreate -i for more detailed and configurable output:

$ mmgen-tool twview
UNSPENT OUTPUTS (sort order: Age) Total BTC: 0.8999
Network: BTC MAINNET
 Num TXid Vout Address                                             Amt(BTC)      Confs
 1)  e3c3..  6 36bNmyYISiptuvJG3X7MPwii.. 89ABCDEF:S:1 Donations      0.1        68
 2)  face..  6 3HgYCsfqYzIg7LVVfDTp7gYJ.. 89ABCDEF:S:3 Storage 2      0.3        68
 3)  abab..  6 34Tu3z1tiexXDonNsFIkvzqu.. 89ABCDEF:S:4 Storage 3      0.4        68
 4)  123c..  6 3PeI55vtp2bX2uKDkAAR2c6e.. 89ABCDEF:S:5                0.0999     7

Since you’ve sent 0.1 BTC to a third party, your balance has decreased by 0.1 BTC plus the transaction fee of 0.0001 BTC.

Congratulations! You’ve now mastered the basics of MMGen Wallet! To learn about some more advanced features, continue reading.

Additional Features

Using the mnemonic, seed and hexseed formats

Using your default wallet from the exercises above, generate a mnemonic seed phrase:

$ mmgen-walletconv -o words
...
Mnemonic data written to file '89ABCDEF.mmwords'

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

Since our seed is 256 bits long, the seed phrase contains 24 words. 128-bit and 192-bit seeds generate shorter mnemonics of 12 and 18 words, respectively. Wallets with these seed lengths can be generated using the --seed-len option to mmgen-walletgen.

Though some consider 128 bits of entropy to provide adequate security for the foreseeable future, it’s advisable to stick to the default 256-bit seed length. You’ll find that even a 24-word seed phrase is not difficult to memorize.

NOTE: MMGen mnemonics are generated from the Electrum wordlist, but using ordinary base conversion instead of Electrum’s more complicated algorithm.

The seed phrase is a complete representation of your seed and may be used anywhere where you’d use a wallet. For example, you can generate addresses with it:

$ mmgen-addrgen --type=segwit 89ABCDEF.mmwords 1-10
...
Address data written to file '89ABCDEF-S[1-10].addrs'

You can use it to sign transactions:

$ mmgen-txsign FEDCBA[0.1].rawtx 89ABCDEF.mmwords
...
Signed transaction written to file 'FEDCBA[0.1].sigtx'

The seed phrase can also be used to regenerate a lost wallet:

$ mmgen-walletconv 89ABCDEF.mmwords
...
MMGen wallet written to file '89ABCDEF-01234567[256,3].mmdat'

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

An alternative to seed phrases, seed files provide yet another way of representing your seed. They bear the extension .mmseed and are generated exactly the same way as mnemonic files:

$ mmgen-walletconv -o seed
...
Seed data written to file '89ABCDEF.mmseed'

They can be used just like mnemonics to regenerate a wallet:

$ mmgen-walletconv 89ABCDEF.mmseed
...
MMGen wallet written to file '89ABCDEF-23456701[256,3].mmdat'

Here’s a sample seed file for a 256-bit seed:

$ 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

As you can see, seed files are short enough to be easily written out by hand or memorized. And their built-in checksum makes it easy to test your memory using a simple Unix shell command:

$ echo -n XnyC NfPH piuW dQ2d nM47 VU | tr -d ' '| sha256sum | cut -c 1-6
0fe02f

Or you can do the same thing with mmgen-tool:

$ mmgen-tool str2id6 'XnyC NfPH piuW dQ2d nM47 VU'
0fe02f

Beginning with version 0.9.0, MMGen Wallet also supports seed files in hexadecimal (hexseed) format. Hexseed files are identical to seed files but encoded in hexadecimal rather than base 58. They bear the extension .mmhex:

$ cat FE3C6545.mmhex
afc3fe 456d 7f5f 1c4b fe3b c916 b875 60ae 6a3e

You can easily check that a hexseed is correct by generating its Seed ID with standard command-line tools:

$ echo 456d 7f5f 1c4b fe3b c916 b875 60ae 6a3e | tr -d ' ' | xxd -r -p | sha256sum -b | xxd -r -p | sha256sum -b | cut -c 1-8
fe3c6545

Mnemonics and hexseeds can be used to generate keys even without the MMGen Wallet software, using basic command-line utilities, as explained in this tutorial.

Mnemonics, seeds and hexseeds: additional information

All MMGen Wallet commands that take mnemonic, seed or hexseed data may receive the data interactively from the user instead of from a file. This feature allows you to store your seed entirely in your head if you wish and never record it on a physical medium. To input your seed data at the prompt, just specify an input format instead of a file name:

$ mmgen-addrgen -i words 1-10
...
Choose a mnemonic length: 1) 12 words, 2) 18 words, 3) 24 words: 1
Mnemonic length of 12 words chosen. OK? (Y/n): y
Enter your 12-word mnemonic, hitting RETURN or SPACE after each word:
Enter word #1:

Here the script will prompt you interactively for each word of the seed phrase, checking it for validity and reprompting if necessary. The words are not displayed on the screen.

As a safeguard against over-the-shoulder, Tempest and other side-channel attacks, MMGen Wallet never outputs secret data to the screen, unless you explicitly ask it to with the --stdout or -S option. And even with this option in effect, you’ll still be prompted before the secret data is actually displayed. This guard prompt is overridden by the --quiet option, however, always think twice before using --stdout together with --quiet.

Files produced by MMGen Wallet’s commands may be written to a directory of your choice using the --outdir or -d option. For example, on a Linux system you can use --outdir=/dev/shm to write keys and seeds to volatile memory instead of disk, ensuring that no trace of your secret data remains once your computer’s been powered down.

Die roll wallet generation

Interactive dieroll wallet generation works just like the interactive mnemonic seed phrase input described in the preceding section. To generate a new dieroll wallet, type:

$ mmgen-walletconv -i dieroll

To save the wallet in a format of your choice, use the -o option:

$ mmgen-walletconv -i dieroll -o bip39

50, 75 and 100 rolls of the die are required to create 128, 192 and 256-bit seeds, respectively.

BIP39 seed phrase support

BIP39 mnemonic seed phrase support and usage is identical to that for native MMGen mnemonics described above. Just use the bip39 format specifier and extension instead of words.

Convert an MMGen native mnemonic wallet to BIP39:

$ mmgen-walletconv -o bip39 mywallet.words

Restore a wallet from a BIP39 seed phrase in a file:

$ mmgen-walletconv seed.bip39

Monero seed phrase support

MMGen Wallet has limited support for Monero new-style mnemonic seed phrases. While they can’t be used as wallets, they’re supported as a password format by the mmgen-passgen command and can be converted to and from hex data by the mmgen-tool mnemonic commands. The format specifier and extension is xmrseed. Only 25-word seed phrases (256-bit keys) are supported. Key data is reduced in accordance with the Monero protocol before conversion, so the resulting seed phrases are guaranteed to be canonical.

Generate a random Monero seed phrase:

$ mmgen-tool mn_rand256 fmt=xmrseed

Generate a list of passwords in Monero mnemonic format with ID ‘foo’ from your default wallet:

$ mmgen-passgen -f xmrseed 'foo' 1-10

Incognito wallets

An incognito format wallet is indistinguishable from random data, allowing you to hide your wallet at an offset within a random-data-filled file or partition. Barring any inside knowledge, a potential attacker has no way of knowing where the wallet is hidden, or whether the file or partition contains anything of interest at all, for that matter.

An incognito wallet with a reasonably secure password could even be hidden on unencrypted cloud storage. Hiding your wallet at some offset in a 1GB file increases the difficulty of any attack by a factor of one billion, assuming again that any potential attacker even knows or suspects you have a wallet hidden there.

If you plan to store your incognito wallet in an insecure location such as cloud storage, you’re advised to use a strong scrypt (hash) preset and a strong password. These can be changed using the mmgen-passchg utility:

$ mmgen-passchg -p 5 89ABCDEF-01234567[256,3].mmdat
...
Hash preset of wallet: '3'
Enter old passphrase for MMGen wallet: <old weak passphrase>
...
Hash preset changed to '5'
Enter new passphrase for MMGen wallet: <new strong passphrase>
...
MMGen wallet written to file '89ABCDEF-87654321[256,5].mmdat'

The scrypt preset is the numeral in the wallet filename following the seed length. As you can see, it’s now changed to 5. Now export your new toughened wallet to incognito format, using the -k option to leave the passphrase unchanged:

$ mmgen-walletconv -k -o incog 89ABCDEF-87654321[256,5].mmdat
...
Reusing passphrase at user request
...
New Incog Wallet ID: ECA86420
...
Incognito data written to file '89ABCDEF-87654321-ECA86420[256,5].mmincog'

Incog wallets have a special identifier, the Incog ID, which can be used to locate the wallet data if you’ve forgotten where you hid it (see the example below). Naturally, an attacker could use this ID to find the data too, so it should be kept secret.

Incog wallets can also be output to hexadecimal format:

$ mmgen-walletconv -k -o incox 89ABCDEF-87654321[256,5].mmdat
...
Hex incognito data written to file '89ABCDEF-87654321-CA86420E[256,5].mmincox'

$ cat 89ABCDEF-87654321-1EE402F4[256,5].mmincox
6772 edb2 10cf ad0d c7dd 484b cc7e 42e9
4fe6 e07a 1ce2 da02 6da7 94e4 c068 57a8
3706 c5ce 56e0 7590 e677 6c6e 750a d057
b43a 21f9 82c7 6bd1 fe96 bad9 2d54 c4c0

Note that the Incog ID is different here: it’s generated from an init vector, which is a different random number each time, making the incog data as a whole different as well. This allows you to store your incog data in multiple public locations without having repeated ‘random’ wallet data give you away.

This data is ideally suited for a paper wallet that could potentially fall into the wrong hands.

Your incognito wallet (whether hex or binary) can be used just like any other wallet, mnemonic or seed file to generate addresses and sign transactions:

$ mmgen-addrgen --type=segwit 89ABCDEF-87654321-CA86420E[256,5].mmincox 101-110
...
Generated 10 addresses
Addresses written to file '89ABCDEF-S[101-110].addrs'

$ mmgen-txsign FABCDE[0.3].rawtx 89ABCDEF-87654321-CA86420E[256,5].mmincox
...
Signed transaction written to file FABCDE[0.3].sigtx

Hidden incognito wallets

With the -o hincog option, incognito wallet data can be created and hidden at a specified offset in a file or partition in a single convenient operation, with the random file being created automatically if necessary. Here’s how you’d create a 1GB file random.dat and hide a wallet in it at offset 123456789:

$ mmgen-walletconv -k -o hincog -J random.dat,123456789 89ABCDEF-87654321[256,5].mmdat
...
New Incog Wallet ID: ED1F2ACB
...
Requested file 'random.dat' does not exist.  Create? (Y/n): Y
Enter file size: 1G
...
Data written to file 'random.dat' at offset 123456789

Your ‘random’ file can now be uploaded to a cloud storage service, for example, or some other, preferably non-public, location on the Internet (in a real-life situation you will choose a less obvious offset than 123456789 though, won’t you?).

Now let’s say at some point in the future you download this file to recover your wallet and realize you’ve forgotten the offset where the data is hidden. If you’ve saved your Incog ID, you’re in luck:

$ mmgen-tool find_incog_data random.dat ED1F2ACB
...
Incog data for ID ED1F2ACB found at offset 123456789

The search process can be slow, so patience is required. In addition, on large files ‘false positives’ are a distinct possibility, in which case you’ll need to use the keep_searching=1 parameter to keep going until you find the real offset.

Hidden incog wallets are nearly as convenient to use as ordinary ones. Generating ten addresses with your hidden incog data is as easy as this:

$ mmgen-addrgen -H random.dat,123456789 101-110

Transaction signing uses the same syntax:

$ mmgen-txsign -H random.dat,123456789 ABCDEF[0.1].rawtx
...
Signed transaction written to file 'ABCDEF[0.1].sigtx'

Advanced Topics

Hot wallets

Instead of using a hot wallet, you should consider setting up transaction autosigning on your offline machine. Autosigning makes it possible to transact directly from cold storage in a secure and convenient way. Ideally, your autosigning device should be a Raspberry Pi or other single-board computer for which MMGen Wallet provides LED support. However, an old laptop running Linux or macOS will also suffice, provided its network interfaces are removed or disabled.

To use MMGen Wallet for not only cold storage but also day-to-day transacting, it’s possible to place a portion of your funds in a “hot wallet” on your online computer. You may then use the mmgen-txdo command to quickly create, sign and send transactions in one operation.

Note: prior to Version 0.11.0, MMGen Wallet implemented hot wallets using key-address files, but these have now been obsoleted by subwallets. Information on key-address files is archived here for the benefit of legacy installations only.

Setting up a hot wallet is easy. Using the Subwallets wiki page as your guide, generate a subwallet on your offline machine for use as a hot wallet. Since this wallet is going to be used in an online environment, make sure it’s protected with a strong password and hash preset.

$ mmgen-subwalletgen -p5 1L
...
MMGen wallet written to file 'FC9A8735-ABCDEF00[256,5].mmdat'

Copy the subwallet to a USB stick or other removable device.

Now on your online computer, check your MMGen data directory for the presence of wallet files:

$ ls $HOME/.mmgen/*.mmdat

If any are present (there shouldn’t be if you’ve been following this guide!), move them out of harm’s way, or copy them to a backup location and securely delete the originals with wipe or sdelete if they’re securing any funds.

Copy the subwallet file to your MMGen data directory, making it your default wallet for the online machine:

$ cp 'FC9A8735-ABCDEF00[256,5].mmdat' $HOME/.mmgen

Securely delete the original file.

Generate a range of addresses with your online default wallet/subwallet and import them into your tracking wallet:

$ mmgen-addrgen --type=bech32 1-10
$ mmgen-addrimport FC9A8735-B*.addrs

Send some coins to an address or addresses in this range using your method of choice.

Now you can spend from these addresses using mmgen-txdo, creating, signing and sending transactions in one operation:

$ mmgen-txdo 1AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc,0.1 FC9A8735:S:2
(choose an input from wallet FC9A8735)
...
Transaction sent: abcd1234....

Bear in mind that your subwallet/online default wallet doesn’t require a backup, as it can always be regenerated from its offline parent. If you ever wish to delete it, however, you should do so securely if there are still funds under its control.

Transaction Fees

MMGen Wallet gives you several options for dealing with transaction fees.

Firstly, and most simply, you may do nothing, in which case the fee will be calculated automatically using bitcoind’s estimatesmartfee RPC call. You can adjust the estimated fee by any factor using the --fee-adj option, a handy feature when you need transactions to confirm a bit more quickly. If network fee estimation fails for any reason, you’ll be prompted to enter the fee manually.

Secondly, you may specify the fee as an absolute BTC amount (a decimal number). This can be done either on the command line or at the interactive prompt when creating transactions with mmgen-txcreate, mmgen-txdo or mmgen-txbump.

Thirdly, instead of using an absolute BTC amount, you may specify the fee in satoshis per byte and let MMGen Wallet calculate the fee based on the transaction size. This also works both on the command line and at the interactive prompt. The satoshis-per-byte specification is an integer followed by the letter s. A fee of 90 satoshis per byte is thus represented as 90s.

MMGen Wallet enforces a hard maximum fee (currently 0.003 BTC) which is alterable only in the config file. Thus the software will never create or broadcast any transaction with a mistakenly or dangerously high fee unless you expressly permit it to.

BIP 125 replace-by-fee (RBF) transactions

As of version 0.9.1, MMGen Wallet supports creating replaceable and replacement transactions in accordance with the BIP 125 replace-by-fee (RBF) specification.

To make your transactions replaceable, just specify the --rbf option when creating them with mmgen-txcreate or mmgen-txdo.

Version 0.9.1 also introduces mmgen-txbump, a convenient command for quickly creating replacement transactions from existing replaceable ones. mmgen-txbump can create, sign and send transactions in a single operation if desired.

Continuing the examples from our primer above, we’ll examine two RBF scenarios, one for a hot wallet and one for a cold storage wallet. In the first scenario, initial and replacement transactions will be created, signed and sent in one operation. In the second, a batch of replacement transactions with incrementally increasing fees will created online and then signed offline.

With an online (hot) wallet

Create, sign and send a BIP 125 replaceable transaction with a fee of 50 satoshis per byte:

$ mmgen-txdo --rbf --fee 50s 1AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc,0.1 0FDE89AB:S:5
...
Signed transaction written to file 'FEDCBB[0.1,50].sigtx'
...
Transaction sent: dcba4321....

Here you’ve sent 0.1 BTC to a third-party address and the change back to yourself at address #5 of your default hot wallet with Seed ID 0FDE89AB.

Note that the fee is shown in the filename after the send amount. The presence of the fee in the filename identifies the transaction as replaceable.

If the transaction fails to confirm in your desired timeframe, then create, sign and send a replacement transaction with a higher fee, say 100 satoshis per byte:

$ mmgen-txbump --send --fee 100s --output-to-reduce c 'FEDCBB[0.1,50].sigtx'
...
Signed transaction written to file 'DAE123[0.1,100].sigtx'
...
Transaction sent: eef01357....

The --send switch instructs mmgen-txbump to sign and send the transaction after creating it. The --output-to-reduce switch with an argument of c requests that the increased fee be deducted from the change (c) output, which is usually what is desired. If you want it taken from some other output, identify the output by number. Note that the resulting replacement transaction has a different identifier, since it’s a new transaction.

If this transaction also fails to confirm, then repeat the above step as many times as necessary to get a confirmation, increasing the fee each time. The only thing you have to modify with each iteration is the argument to --fee. To reduce your typing even further, use the --yes switch to skip all non-essential prompts.

With an offline (cold storage) wallet

To achieve the same result as in the above example using a cold wallet, just create the initial transaction with mmgen-txcreate instead of mmgen-txdo:

$ mmgen-txcreate --rbf --fee 50s 1AmkUxrfy5dMrfmeYwTxLxfIswUCcpeysc,0.1 89ABCDEF:S:5
...
Transaction written to file 'FEDCBC[0.1,50].rawtx'

Now create a series of transactions with incrementally increasing fees for offline signing:

$ mmgen-txbump --fee 100s --output-to-reduce c 'FEDCBC[0.1,50].rawtx'
$ mmgen-txbump --fee 150s --output-to-reduce c 'FEDCBC[0.1,50].rawtx'
$ mmgen-txbump --fee 200s --output-to-reduce c 'FEDCBC[0.1,50].rawtx'

To speed things up, add the --yes switch to make mmgen-txbump completely non-interactive.

The result will be four raw transaction files with increasing fees, like this:

FEDCBC[0.1,50].rawtx
3EBB00[0.1,100].rawtx
124FFF[0.1,150].rawtx
73DABB[0.1,200].rawtx

Copy the files to an empty folder, transfer the folder to your offline machine and batch sign them:

$ mmgen-txsign -d my_folder --yes my_folder/*.rawtx

Then copy the signed transaction files back to your online machine and broadcast them in turn until you get a confirmation:

$ mmgen-txsend FEDCBC[0.1,50].sigtx   # ...if this doesn’t confirm, then
$ mmgen-txsend 3EBB00[0.1,100].sigtx  # ...if this doesn’t confirm, then
$ mmgen-txsend 124FFF[0.1,150].sigtx  # ...if this doesn’t confirm, then
$ mmgen-txsend 73DABB[0.1,200].sigtx

Keeping your installation up to date

To make sure you have all the latest features and bugfixes, it’s a good idea to keep your MMGen Wallet installation upgraded to the latest version. The software does no checking for updates, so it’s up to you to do so yourself on a periodic basis.

Stable version:

To update the stable version, simply perform:

$ python3 -m pip install --update mmgen-wallet

For an offline installation, download the package on your online machine with pip download, transfer the downloaded package to your offline machine and install it with pip install --no-isolation.

Note that additional dependencies may appear from version to version, causing an offline installation to fail. Consult the latest release notes in doc/release-notes or your platform’s installation page in the wiki (Linux, macOS, Windows) for more information.

Development version:

If you’ve deleted or lost your local copy of the MMGen Wallet repository, clone it again from Github, Gitlab or mmgen.org:

$ git clone https://github.com/mmgen/mmgen-wallet.git
$ git clone https://gitlab.com/mmgen/mmgen-wallet.git
$ git clone https://mmgen.org/project/mmgen/mmgen-wallet.git

Enter the repository and check out the master branch. Pull the latest changes from the remote repository:

$ cd mmgen-wallet
$ git checkout master
$ git pull

Newly added features may not yet be covered in the documentation, but you may often find information on them by invoking git log or visiting the online commits page.

Now build and install:

$ rm -rf dist build *.egg-info
$ python3 -m build --no-isolation
$ python3 -m pip install user --upgrade dist/*.whl

Getting-Started-with-MMGen-Wallet.md

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