diceware

Passphrases to remember...

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diceware is a passphrase generator following the proposals of Arnold G. Reinhold on http://diceware.com . It generates passphrases by concatenating words randomly picked from wordlists. For instance:

$ diceware
MyraPend93rdSixthEagleAid

The passphrase contains by default six words (with first char capitalized) without any separator chars. Optionally you can let diceware insert special chars into the passphrase.

diceware supports several sources of randomness (including real life dice) and different wordlists (including cryptographically signed ones).

Install

This Python package can be installed via pip:

$ pip install diceware

The exact way depends on your operating system.

Usage

Once installed, use --help to list all available options:

$ diceware --help
Create a passphrase

positional arguments:
  INFILE                Input wordlist. `-' will read from stdin.

optional arguments:
  -h, --help            show this help message and exit
  -n NUM, --num NUM     number of words to concatenate. Default: 6
  -c, --caps            Capitalize words. This is the default.
  --no-caps             Turn off capitalization.
  -s NUM, --specials NUM
                        Insert NUM special chars into generated word.
  -d DELIMITER, --delimiter DELIMITER
                        Separate words by DELIMITER. Empty string by default.
  -r SOURCE, --randomsource SOURCE
                        Get randomness from this source. Possible values:
                        `realdice', `system'. Default: system
  -w NAME, --wordlist NAME
                        Use words from this wordlist. Possible values: `en',
                        `en_eff', `en_orig', `en_securedrop'. Wordlists are
                        stored in the folder displayed below. Default: en_eff
  -v, --verbose         Be verbose. Use several times for increased verbosity.
  --version             output version information and exit.

Arguments related to `realdice' randomsource:
  --dice-sides N        Number of sides of dice. Default: 6

Wordlists are stored in <WORDLISTS-DIR>

With -n you can tell how many words are supposed to be picked for your new passphrase:

$ diceware -n 1
Thud

$ diceware -n 2
KnitMargo

You can diceware additionally let generate special chars to replace characters in the 'normal' passphrase. The number of special chars generated can be determined with the -s option (default is zero):

$ diceware -s 2
Heroic%unkLon#DmLewJohns

Here "%" and "#" are the special chars.

Special chars are taken from the following list:

~!#$%^&*()-=+[]\{}:;\"'<>?/0123456789

Please note that several special chars might replace the same original char, resulting in a passphrase with less special chars than requested.

With -d you can advise diceware to put a delimiter string between the words generated:

$ diceware -d "_"
Wavy_Baden_400_Whelp_Quest_Macon

By default we use the empty string as delimiter, which is good for copying via double click on Linux systems. But other delimiters might make your passphrases more readable (and more secure, see Security Traps below).

By default the single phrase words are capitalized, i.e. the first char of each word is made uppercase. This does not neccessarily give better entropy (but protects against entropy loss due to non prefix code, see Security Traps below), and it might improve phrase readability.

You can nevertheless disable caps with the --no-caps option:

$ diceware --no-caps
oceanblendbaronferrylistenvalet

This will leave the input words untouched (upper-case stays upper-case, lower-case stays lower-case). It does not mean, that all output words will be lower-case (except if all words of your wordlist are lowercase).

As the default lists of diceware contain only lower-case terms, here --no-caps means in fact lower-case only output, which might be easier to type on smart phones and similar.

diceware supports also different sources of randomness, which can be chosen with the -r <SOURCENAME> or --randomsource <SOURCENAME> option. Use the --help option to list all valid values for this option.

By default we use the random.SystemRandom class of standard Python lib but you can also bring your own dice to create randomness:

$ diceware -r realdice --dice-sides 6
Please roll 5 dice (or a single dice 5 times).
What number shows dice number 1? 2
What number shows dice number 2? 3
...
DogmaAnyShrikeSageSableHoar

Normally dice have six sides. And this is also the default in diceware if you do not use --dice-sides. But if you do, you can tell how many sides (all) your dice have. More sides will lead to less rolls required.

We support even sources of randomness from other packages. See the documentation for more details.

diceware comes with an English wordlist provided by the EFF, which will be used by default and contains 7776 (=6^5) different words. This list is registered as en_eff.

Additionally diceware comes with an English wordlist provided by @heartsucker, which contains 8192 different words. This list is based off the original diceware list written by Arnold G. Reinhold.

Both the original and 8k diceware wordlists by Mr. Reinhold are provided. You can enable a certain (installed) wordlist with the -w option:

$ diceware --wordlist en_orig
YorkNodePrickEchoToriNiobe

See diceware --help for a list of all installed wordlists.

If you do not like the wordlists provided, you can use your own one. Any INFILE provided will be parsed line by line and each line considered a possible word. For instance:

$ echo -e "hi\nhello\n" > mywordlist.txt
$ diceware mywordlist.txt
HelloHelloHiHiHiHello

With dash (-) as filename you can pipe in wordlists:

$ echo -e "hi\nhello\n" | diceware -
HiHiHelloHiHiHello

In custom wordlists we take each line for a valid word and ignore empty lines (i.e. lines containing whitespace characters only). Oh, and we handle even PGP-signed wordlists.

You can set customized default values in a configuration file .diceware.ini (note the leading dot) placed in your home directory. This file could look like this:

[diceware]
num = 7
caps = off
specials = 2
delimiter = "MYDELIMITER"
randomsource = "system"
wordlist = "en_securedrop"

The options names have to match long argument names, as output by --help. The values set must meet the requirements valid for commandline usage. All options must be set within a section [diceware].

What is it good for?

Normally, diceware passphrases are easier to remember than shorter passwords constructed in more or less bizarre ways. But at the same time diceware passphrases provide more entropy as xkcd can show with the famous '936' proof:

The standard english wordlist of this diceware implementation contains 7776 = 6^5 different english words. It is the official EFF wordlist. compiled by Joseph Bonneau. Therefore, picking a random word from this list gives an entropy of nearly 12.9 bits. Picking six words means an entropy of 6 x 12.9 = 77.54 bits.

The special chars replacing chars of the originally created passphrase give some more entropy (the more chars you have, the more additional entropy), but not much. For instance, for a sixteen chars phrase you have sixteen possibilities to place one of the 36 special chars. That makes 36 x 16 possibilitities or an entropy of about 9.17 you can add. To get an entropy increase of at least 10 bits, you have to put a special char in a phrase with at least 29 chars (while at the same time an additional word would give you 13 bits of extra entropy). Therefore you might think again about using special chars in your passphrase.

Is it secure?

The security level provided by Diceware depends heavily on your source of random. If the delivered randomness is good, then your passphrases will be very strong. If instead someone can foresee the numbers generated by a random number generator, your passphrases will be surprisingly weak.

This Python implementation uses (by default) the random.SystemRandom source provided by Python. On Un*x systems it accesses /dev/urandom. You might want to follow reports about manipulated random number generators in operating systems closely.

The Python API of this package allows usage of other sources of randomness when generating passphrases. This includes real dice. See the -r option.

Security Traps

There are issues that might reduce the entropy of the passphrase generated. One of them is the prefix code problem:

Prefix Code

If the wordlist contains, for example, the words:

"air", "airport", "portable", "able"

and we switched off caps and delimiter chars, then diceware might generate a passphrase containing:

"airportable"

which could come from air-portable or airport-able. We cannot tell and an attacker would have less combinations to guess.

To avoid that, you can leave caps enabled (the default), use any word delimiter except the empty string or use the en_eff wordlist, which was checked to be a prefix code (i.e. it does not contain words that start with other words in the list).

Each of these measures is sufficient to protect you against the prefix code problem.

Reduced Entropy

Overall, diceware is a kind of mapping input values, dice throws for instance, onto wordlist entries. We normally want each of the words in the wordlist to be picked for passphrases with the same probability.

This, however, is not possible, if the number of wordlist entries is not a power of dice sides. In that case we cut some words of the wordlist and inform the user about the matter. Reducing the number of words this way makes it easier for attackers to guess the phrase picked.

You can fix that problem by using longer wordlists.

Developer Install

Developers want to fork me on github:

$ git clone https://github.com/ulif/diceware.git

We recommend to create and activate a virtualenv first:

$ cd diceware/
$ virtualenv -p /usr/bin/python3.4 py34
$ source py34/bin/activate
(py34) $

We support Python versions 2.6, 2.7, 3.3 to 3.6, and pypy.

Now you can create the devel environment:

(py34) $ python setup.py dev

This will fetch test packages (py.test). You should be able to run tests now:

(py34) $ py.test

If you have also different Python versions installed you can use tox for using them all for testing:

(py34) $ pip install tox   # only once
(py34) $ tox

Should run tests in all supported Python versions.

Documentation Install

The docs can be generated with Sphinx. The needed packages are installed via:

(py34) $ python setup.py docs

To create HTML you have to go to the docs/ directory and use the prepared Makefile:

(py34) $ cd docs/
(py34) $ make

This should generate the docs in docs/_build/html/.

Creating the Man Page

We provide a ReStructuredTexT template to create a man page. When the documentation engine is installed (Sphinx, see above), then you can create a manpage doing:

(py34) $ rst2man.py docs/manpage.rst > diceware.1

The template is mainly provided to ease the job of Debian maintainers. Currently, it is not automatically updated. Dates, authors, synopsis, etc. have to be updated manually. Information in the manpage may therefore be wrong, outdated, or simply misleading.

Credits

Arnold G. Reinhold deserves all merits for the working parts of Diceware. The non-working parts are certainly my fault.

People that helped spotting bugs, providing solutions, etc.:

• Conor Schaefer (conorsch)
• Rodolfo Gouveia suggested to activate the --delimiter option.
• @drebs provided patches and discussion for different sources of randomness. @drebs also initiated and performed the packaging of diceware for the Debian platform. Many kudos for this work! @drebs is also the official Debian maintainer of the diceware package.
• @heartsucker hand-compiled and added a new english wordlist.
• dwcoder revealed and fixed bugs #19, #21, #23. Also showed sound knowledge of (theoretical) entropy. A pleasure to work with.
• George V. Reilly pointed to new EFF wordlists.
• lieryan brought up the prefix code problem.
• LogosOfJ discovered and fixed serious realdice source of randomness problem.
• Bhavin Gandhi fixed the confusing error message when an invalid input filename is given.
• Simon Fondrie-Teitler contributed a machine-readable copyright file, with improvements from @anarcat
• Doug Muth fixed formatting in docs.

Many thanks to all of them!

Links

• The Diceware home page. Reading definitely recommended!
• fork me on github

Wordlists:

• Diceware standard list by Arnold G. Reinhold.
• Diceware8k list by Arnold G. Reinhold.
• Diceware SecureDrop list by @heartsucker.
• EFF large list provided by EFF.

License

This Python implementation of Diceware, (C) 2015-2018 Uli Fouquet, is licensed under the GPL v3+. See file LICENSE for details.

"Diceware" is a trademark of Arnold G Reinhold, used with permission.

The copyright for the Diceware8k list is owned by Arnold G Reinhold. The copyright for the the Diceware SecureDrop list are owned by @heartsucker. Copyright for the EFF large list by Joseph Bonneau and EFF. See file COPYRIGHT for details.