test-cases: add support for encrypted corpus

[samiraguiar]

To avoid triggering antivirus engines, we can encrypt
files with a default password and decrypt them before
testing.

Closes #215

[samiraguiar]

@christian-intra2net encrypting files ends up breaking your unit test for json output. Do you have any suggestions on how to proceed?
I cannot pass the zip password to olevba since xglob would try to unzip all of the files, and not just the ones that are actually zipped. Also, there doesn't seem to be a way to exclude files from the iteration.

[christian-intra2net]

Just stumbled over this, must have missed a notification I got referenced here.

I guess the json unit test fails because it iterates over all files in tests/test-data and checks if running olevba[3]/msodde -j creates valid json, right. What does it produce for the encrypted zip? Did my last pull request solve this? Otherwise, what is the error?

[decalage2]

Here's the error I see in the Travis CI logs:

======================================================================
ERROR: test_rough_doctype (tests.ooxml.test_basic.TestOOXML)
Checks all samples, expect either ole files or good ooxml output
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/decalage2/oletools/tests/ooxml/test_basic.py", line 62, in test_rough_doctype
    acceptable = ext2doc[extn]
KeyError: 'zip'

[christian-intra2net]

I see, then there is an easy fix which is adding "zip" to except_extns in tests.ooxml.test_basic.TestOOXML.test_rough_doctype . It will then ignore that file.

Extending every test, that loops over all test data, to deal with encrypted zip files is probably not worth the effort, except if we plan on having lots more of zip-encrypted examples. In that case every "test-data walk()ing" test would have to be adapted (only a few at the moment).

[samiraguiar]

Thanks for the hint @christian-intra2net, it's fixed now.