msoffcrypto-tool

msoffcrypto-tool (formerly ms-offcrypto-tool) is Python tool and library for decrypting encrypted MS Office files with password, intermediate key, or private key which generated its escrow key.

Contents

• Install
• Examples
• Supported encryption methods
• Tests
• Todo
• Resources
• Use cases and mentions
• Contributors

Install

pip install msoffcrypto-tool

Examples

As CLI tool (with password)

msoffcrypto-tool encrypted.docx decrypted.docx -p Passw0rd

Password is prompted if you omit the password argument value:

$ msoffcrypto-tool encrypted.docx decrypted.docx -p
Password:

Test if the file is encrypted or not (exit code 0 or 1 is returned):

msoffcrypto-tool document.doc --test -v

As library

Password and more key types are supported with library functions.

Basic usage:

import msoffcrypto

encrypted = open("encrypted.docx", "rb")
file = msoffcrypto.OfficeFile(encrypted)

file.load_key(password="Passw0rd")  # Use password

with open("decrypted.docx", "wb") as f:
    file.decrypt(f)

encrypted.close()

Basic usage (in-memory):

import msoffcrypto
import io
import pandas as pd

decrypted = io.BytesIO()

with open("encrypted.xlsx", "rb") as f:
    file = msoffcrypto.OfficeFile(f)
    file.load_key(password="Passw0rd")  # Use password
    file.decrypt(decrypted)

df = pd.read_excel(decrypted)
print(df)

Advanced usage:

# Verify password before decryption (default: False)
# The ECMA-376 Agile/Standard crypto system allows one to know whether the supplied password is correct before actually decrypting the file
# Currently, the verify_password option is only meaningful for ECMA-376 Agile/Standard Encryption
file.load_key(password="Passw0rd", verify_password=True)

# Use private key
file.load_key(private_key=open("priv.pem", "rb"))

# Use intermediate key (secretKey)
file.load_key(secret_key=binascii.unhexlify("AE8C36E68B4BB9EA46E5544A5FDB6693875B2FDE1507CBC65C8BCF99E25C2562"))

# Check the HMAC of the data payload before decryption (default: False)
# Currently, the verify_integrity option is only meaningful for ECMA-376 Agile Encryption
file.decrypt(open("decrypted.docx", "wb"), verify_integrity=True)

Supported encryption methods

MS-OFFCRYPTO specs

• ECMA-376 (Agile Encryption/Standard Encryption)
  • MS-DOCX (OOXML) (Word 2007-2016)
  • MS-XLSX (OOXML) (Excel 2007-2016)
  • MS-PPTX (OOXML) (PowerPoint 2007-2016)
• Office Binary Document RC4 CryptoAPI
  • MS-DOC (Word 2002, 2003, 2004)
  • MS-XLS (Excel 2002, 2003, 2004) (experimental)
  • MS-PPT (PowerPoint 2002, 2003, 2004) (partial, experimental)
• Office Binary Document RC4
  • MS-DOC (Word 97, 98, 2000)
  • MS-XLS (Excel 97, 98, 2000) (experimental)
• ECMA-376 (Extensible Encryption)
• XOR Obfuscation

Other

• Word 95 Encryption (Word 95 and prior)
• Excel 95 Encryption (Excel 95 and prior)
• PowerPoint 95 Encryption (PowerPoint 95 and prior)

PRs are welcome!

Tests

With coverage and pytest:

poetry install
poetry run coverage run -m pytest -v

Todo

• Add tests
• Support decryption with passwords
• Support older encryption schemes
• Add function-level tests
• Add API documents
• Publish to PyPI
• Add decryption tests for various file formats
• Integrate with more comprehensive projects handling MS Office files (such as oletools?) if possible
• Add the password prompt mode for CLI
• Improve error types (v4.12.0)
• Redesign APIs (v6.0.0)
• Introduce something like ctypes.Structure
• Support encryption
• Isolate parser

Resources

• "Backdooring MS Office documents with secret master keys" http://secuinside.com/archive/2015/2015-1-9.pdf
• Technical Documents https://msdn.microsoft.com/en-us/library/cc313105.aspx
  • [MS-OFFCRYPTO] Agile Encryption https://msdn.microsoft.com/en-us/library/dd949735(v=office.12).aspx
• [MS-OFFDI] Microsoft Office File Format Documentation Introduction https://learn.microsoft.com/en-us/openspecs/office_file_formats/ms-offdi/24ed256c-eb5b-494e-b4f6-fb696ad2b4dc
• LibreOffice/core https://github.com/LibreOffice/core
• LibreOffice/mso-dumper https://github.com/LibreOffice/mso-dumper
• wvDecrypt http://www.skynet.ie/~caolan/Packages/wvDecrypt.html
• Microsoft Office password protection - Wikipedia https://en.wikipedia.org/wiki/Microsoft_Office_password_protection#History_of_Microsoft_Encryption_password
• office2john.py https://github.com/magnumripper/JohnTheRipper/blob/bleeding-jumbo/run/office2john.py

Alternatives

• herumi/msoffice https://github.com/herumi/msoffice
• DocRecrypt https://blogs.technet.microsoft.com/office_resource_kit/2013/01/23/now-you-can-reset-or-remove-a-password-from-a-word-excel-or-powerpoint-filewith-office-2013/
• Apache POI - the Java API for Microsoft Documents https://poi.apache.org/

Use cases and mentions

General

• https://repology.org/project/python:msoffcrypto-tool/versions (kudos to maintainers!)
• https://checkroth.com/unlocking-password-protected-files.html

Malware/maldoc analysis

• https://github.com/jbremer/sflock/commit/3f6a96abe1dbb4405e4fb7fd0d16863f634b09fb
• https://isc.sans.edu/forums/diary/Video+Analyzing+Encrypted+Malicious+Office+Documents/24572/

CTF

• https://github.com/shombo/cyberstakes-writeps-2018/tree/master/word_up
• https://github.com/willi123yao/Cyberthon2020_Writeups/blob/master/csit/Lost_Magic

In other languages

• https://github.com/dtjohnson/xlsx-populate
• https://github.com/opendocument-app/OpenDocument.core/blob/233663b039/src/internal/ooxml/ooxml_crypto.h
• https://github.com/jaydadhania08/PHPDecryptXLSXWithPassword

In publications

• Excel、データ整理＆分析、画像処理の自動化ワザを完全網羅！ 超速Python仕事術大全 (伊沢剛, 2022)
• "Analyse de documents malveillants en 2021", MISC Hors-série N° 24, "Reverse engineering : apprenez à analyser des binaires" (Lagadec Philippe, 2021)
• シゴトがはかどる Python自動処理の教科書 (クジラ飛行机, 2020)

Contributors

• https://github.com/nolze/msoffcrypto-tool/graphs/contributors