xortool

xortool.py

A tool to do some xor analysis:

• guess the key length (based on count of equal chars)
• guess the key (base on knowledge of most frequent char)

Notice: xortool is now only running on Python 3. The old Python 2 version is accessible at the py2 branch. The pip package has been updated.

Installation

$ pip3 install xortool

For development or building this repository, poetry is needed.

poetry build
pip install dist/xortool*.whl

Usage

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Example 1

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The most common use is to pass just the encrypted file and the most frequent character (usually 00 for binaries and 20 for text files) - length will be automatically chosen:

tests $ xortool tool_xored -c 20
The most probable key lengths:
   2:   5.6%
   5:   7.8%
   8:   6.0%
  10:   11.7%
  12:   5.6%
  15:   7.6%
  20:   19.8%
  25:   7.8%
  28:   5.7%
  30:   11.4%
Key-length can be 5*n
1 possible key(s) of length 20:
an0ther s3cret \xdd key

Here, the key is longer then default 32 limit:

tests $ xortool ls_xored -c 00 -m 64
The most probable key lengths:
   3:   3.3%
   6:   3.3%
   9:   3.3%
  11:   7.0%
  22:   6.9%
  24:   3.3%
  27:   3.2%
  33:   18.4%
  44:   6.8%
  55:   6.7%
Key-length can be 3*n
1 possible key(s) of length 33:
really long s3cr3t k3y... PADDING

So, if automated decryption fails, you can calibrate:

• (-m) max length to try longer keys
• (-l) selected length to see some interesting keys
• (-c) the most frequent char to produce right plaintext

Example 2

We are given a message in encoded in Base64 and XORed with an unknown key.

# xortool message.enc
The most probable key lengths:
   2:   12.3%
   4:   13.8%
   6:   10.5%
   8:   11.5%
  10:   8.6%
  12:   9.4%
  14:   7.1%
  16:   7.8%
  23:   10.4%
  46:   8.7%
Key-length can be 4*n
Most possible char is needed to guess the key!

We can now test the key lengths while filtering the outputs so that it only keeps the plaintexts holding the character set of Base64. After trying a few lengths, we come to the right one, which gives only 1 plaintext with a percentage of valid characters above the default threshold of 95%.

$ xortool message.enc -b -f -l 23 -t base64
256 possible key(s) of length 23:
\x01=\x121#"0\x17\x13\t\x7f ,&/\x12s\x114u\x170#
\x00<\x130"#1\x16\x12\x08~!-\'.\x13r\x105t\x161"
\x03?\x103! 2\x15\x11\x0b}".$-\x10q\x136w\x152!
\x02>\x112 !3\x14\x10\n|#/%,\x11p\x127v\x143
\x059\x165\'&4\x13\x17\r{$("+\x16w\x150q\x134\'
...
Found 1 plaintexts with 95.0%+ valid characters
See files filename-key.csv, filename-char_used-perc_valid.csv

By filtering the outputs on the character set of Base64, we directly keep the only solution.

Information

Author: hellman

License: MIT License