Worked-Out Example 0¶
Decrypting a Password¶
Problem: crack an encrypted file by brute force. Assume that the password is a five-letter lower-case word and that you know that the plain text contains my name.
(The complete code for this example and a secret message comes with the jug source)
This is the ultimate parallel problem: try very many keys (26**5 ~ 11M), but there is no interaction between the different tasks.
The brute force version is very simple:
for p in product(letters, repeat=5): text = decode(ciphertext, p) if isgood(text): passwd = "".join(map(chr, p)) print('%s:%s' % (passwd, text))
However, if we have more than one processor, we’d like to be able to tell
jug to use multiple processors.
We cannot simply have each password be its own task: 11M tasks would be too much!
So, we are going to iterate over the first letter and a task will consist of trying every possibility starting with that letter:
@TaskGenerator def decrypt(prefix, suffix_size): res =  for p in product(letters, repeat=suffix_size): text = decode(ciphertext, np.concatenate([prefix, p])) if isgood(text): passwd = "".join(map(chr, p)) res.append((passwd, text)) return res @TaskGenerator def join(partials): return list(chain(*partials)) fullresults = join([decrypt([let], 4) for let in letters])
decrypt function returns a list of all the good passwords it
found. To simplify things, we call the
join function which concatenates all
the partial results into a single list for convenience.
$ jug execute jugfile.py & $ jug execute jugfile.py & $ jug execute jugfile.py & $ jug execute jugfile.py &
You can run as many simultaneous processes as you have processors. To see what is happening, type:
$ jug status jugfile.py
And you will get an output such as:
Task name Waiting Ready Finished Running ---------------------------------------------------------------------------------------- jugfile.join 1 0 0 0 jugfile.decrypt 0 14 8 4 ........................................................................................ Total: 1 14 8 4
There are two task functions:
decrypt, of which 8 are finished, 14 are ready
to run, and 4 are currently running; and
join which has a single instance,
waiting: it cannot run until all the
decrypt tasks have
Eventually, everything will be finished and your results will be saved in
jugdata in files with names such as
jugdata/5/4/a1266debc307df7c741cb7b997004f The name is simply a hash of the
task description (function and its arguments).
In order to make sense of all of this, we write a final script, which loads the results and prints them on stdout:
import jug jug.init('jugfile.py', 'jugdata') import jugfile results = jug.task.value(jugfile.fullresults) for p, t in results: print("%s\n\n Password was '%s'" % (t, p))
jug.init takes the jugfile name (which happens to be
the data directory name.
jug.task.value takes a
jug.Task and loads its result. It handles more
complex cases too, such as a list of tasks (and returns a list of their