Making random memorable passwords with bash

Making secure passwords is quite a common task, and there are plenty of random password generators around (I like the one in keepassx). Making memorable passwords can be a bit trickier, though.

A nice way to make random but memorable passwords is to use a sequence of words and perhaps a short number (obligatory link to xkcd). That kind of password is easy for a human to remember and generally hard to brute-force, so long as the pool of possible words is large enough.

Most Linux distros come with long lists of words in dictionary files. For example, on Ubuntu there are several word-list files in /usr/share/dict, and it looks like they’re long enough for this purpose; wc -l /usr/share/dict /british-english gives 99156, which should be sufficiently unpredictable.

We can get as many random words we want with shuf:

shuf -n 3 /usr/share/dict/british-english

Which gives you something like this:

cargoes
cowboys
reallocating

(There’s always something interesting about randomly selected words. I think in an effect similar to apophenia, we tend to see the combination as meaningful. Feel free to use the above command for your daily horoscope.)

It’s not ideal that the randomly selected words are on separate lines, though. We can tidy that up piping to tr like this:

shuf -n 3 /usr/share/dict/british-english | tr -d "\n"

And we get something that looks more like a usable password:

nutdefensivecrocodile

However, it’s difficult to distinguish the inidividual words, and we’re trying to create memorable passwords here. That can be fixed by piping the lines through sed first to capitalise the first letter:

shuf -n 3 /usr/share/dict/british-english | sed 's/./\u&/' | tr -d "\n"

That produces things like the following:

SpyingClinicDucked
TeleconferencedVagabondedBundles
WrigglyVaguestCheesecloth

(I’m not making these up.)

A lot of systems require a mix of letters and numbers in passwords, and adding some digits can’t hurt the security of the password either. That can also be achieved with shuffle:

shuf -n 3 /usr/share/dict/british-english | sed 's/./\u&/'  | tr -d "\n'"; echo $(shuf -i0-999 -n 1)

That has the added benefit of getting a newline character at the end of the output as well.

The final thing I’d change is to have the tr command remove anything that’s not a letter, as apostrophes and other bits and pieces reduce memorability without adding a lot to the security of the password (you can increase the number of words and digits if that’s a concern):

shuf -n 3 /usr/share/dict/british-english | sed 's/./\u&/' | tr -cd '[A-Za-z]'; echo $(shuf -i0-999 -n 1)

And now we have a convenient random memorable password generator in one line of bash.

IngestImbalancesIndeed473
EditionGasserVolleyed983
EmbracesPinstripePortlier145
DistantlyAlonzoMahjong603
QualifyLeechedSodas713

I’ve got the command aliased to mempass and it’s pretty handy.

alias mempass='shuf -n 3 /usr/share/dict/british-english | sed "s/./\u&/" | tr -cd "[A-Za-z]"; echo $(shuf -i0-999 -n 1)'

Notice the single quotes around the whole alias with double quotes inside. If you do it the other way round, the echo command at the end is run once when assigning the alias, so you’d get the same digits at the end of every generated password.