Cracking Microsoft Office password protection via hashcat, locally or in the cloud

This guide covers cracking a password-protected DOCX file¹ created with Word for Mac 2011 (which employs the same protection algorithm as Microsoft Word 2010). It also largely applies to cracking any hash supported by hashcat (MD5, SHA1, NTLM, etc).

1. Cracking locally

Test platform: a wildly unsuitable mid-2010 iMac with an Intel Core i3 processor and 256MB ATI Radeon HD 4670 graphics card, running macOS 10.12. We won't bother attempting a brute force / mask attack, since even a simple 6-character lowercase password could take as long as 19 years to crack on this hardware.

1.1 Retrieve hash

Download and run office2hashcat.py to retrieve and save the encrypted hash of our password-protected Word document (foo.docx) to hash.txt:²

The hash is identified as MS Office 2010, which is assigned the hash mode number 9500 by hashcat (see hashcat --help for a list of all hash modes).

1.2 Get hashcat and OpenCL-Headers

1.3 Get wordlist

1.4 Start cracking

-a 0 = set attack mode to straight / dictionary attack
-m 9500 = set hash mode to MS Office 2010
--status = automatically update status screen
-o found.txt = output recovered password to found.txt
hash.txt = the hash we saved in step 1.1
merged.txt = our wordlist from step 1.3

What happened? The GPU is unsupported³ and hashcat halts immediately. We can force hashcat to use the CPU with --opencl-device-types 1:

which cracked the hash for what turned out to be a 6 character lowercase password in about 12.5 hours:

2. Cracking in the cloud

2.1 Create AWS EC2 p2.16xlarge instance

2.2 Enable inbound SSH and connect from Mac

2.3 Setup server

2.3.1 Update Ubuntu

2.3.2 Disable Nouveau driver

2.3.3 Install NVIDIA driver

2.3.4 Optimize GPU settings

2.4 Get hashcat, OpenCL-Headers, and wordlist

2.5 Upload hash from Mac to p2.16xlarge instance

2.6 Dictionary / wordlist / straight attack

2.7 Brute-force / mask attack

We'll cheat a bit and restrict the attack to a maximum of just 8 lowercase letters. Arguments that differ from section 1.4 above:

-a 3 = set attack mode to brute-force / mask
?l?l?l?l?l?l?l?l = set mask to 8 lowercase letters
--increment = start with 1 character and attack up to max of 8 set by mask

2.8 Terminate instance

3. Footnotes

Unrelated to the trivial "Restrict Editing" or "locking" feature.
Or use office2john.py, but you'll then need to specify --username in the command line arguments to ignore the filename and colon that office2john prepends to the output.

A cursory attempt at tweaking /hashcat/src/opencl.c by removing the if statements for base atomics, byte-addressable store, and local mem size did indeed allow the GPU to be utilized along with the CPU, halving the run time. Alas, the result was less than desirable:

Session..........: hashcat                                
Status...........: Exhausted
Hash.Type........: MS Office 2010
Hash.Target......: $office$*2010*100000*128*16*a1688e8975694550a7a61b5...2ed49a
Time.Started.....: Sun Aug 20 14:50:19 2017 (8 hours, 17 mins)
Time.Estimated...: Sun Aug 20 23:07:33 2017 (0 secs)
Guess.Base.......: File (merged.txt)
Guess.Queue......: 1/1 (100.00%)
Speed.Dev.#1.....:      236 H/s (0.25ms)
Speed.Dev.#2.....:      329 H/s (6.56ms)
Speed.Dev.#*.....:      565 H/s
Recovered........: 0/1 (0.00%) Digests, 0/1 (0.00%) Salts

For a lengthier process (albeit with more options, including Security Groups), click "Next: Configure Instance Details" instead.

tinyapps.org / docs / Cracking Microsoft Office password protection via hashcat, locally or in the cloud