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.
$ pip3 install xortoolFor development or building this repository, poetry is needed.
poetry build
pip install dist/xortool*.whlxortool
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)
Usage:
xortool [-x] [-m MAX-LEN] [-f] [-t CHARSET] [FILE]
xortool [-x] [-l LEN] [-c CHAR | -b | -o] [-f] [-t CHARSET] [-p PLAIN] [FILE]
xortool [-x] [-m MAX-LEN| -l LEN] [-c CHAR | -b | -o] [-f] [-t CHARSET] [-p PLAIN] [FILE]
xortool [-h | --help]
xortool --version
Options:
-x --hex input is hex-encoded str
-l LEN, --key-length=LEN length of the key
-m MAX-LEN, --max-keylen=MAX-LEN maximum key length to probe [default: 65]
-c CHAR, --char=CHAR most frequent char (one char or hex code)
-b --brute-chars brute force all possible most frequent chars
-o --brute-printable same as -b but will only check printable chars
-f --filter-output filter outputs based on the charset
-t CHARSET --text-charset=CHARSET target text character set [default: printable]
-p PLAIN --known-plaintext=PLAIN use known plaintext for decoding
-h --help show this help
Notes:
Text character set:
* Pre-defined sets: printable, base32, base64
* Custom sets:
- a: lowercase chars
- A: uppercase chars
- 1: digits
- !: special chars
- *: printable chars
Examples:
xortool file.bin
xortool -l 11 -c 20 file.bin
xortool -x -c ' ' file.hex
xortool -b -f -l 23 -t base64 message.enc
xortool -b -p "xctf{" message.enc
# xor is xortool/xortool-xor
tests $ xor -f /bin/ls -s "secret_key" > binary_xored
tests $ xortool binary_xored
The most probable key lengths:
2: 5.0%
5: 8.7%
8: 4.9%
10: 15.4%
12: 4.8%
15: 8.5%
18: 4.8%
20: 15.1%
25: 8.4%
30: 14.9%
Key-length can be 5*n
Most possible char is needed to guess the key!
# 00 is the most frequent byte in binaries
tests $ xortool binary_xored -l 10 -c 00
...
1 possible key(s) of length 10:
secret_key
# decrypted ciphertexts are placed in ./xortool_out/Number_<key repr>
# ( have no better idea )
tests $ md5sum xortool_out/0_secret_key /bin/ls
29942e290876703169e1b614d0b4340a xortool_out/0_secret_key
29942e290876703169e1b614d0b4340a /bin/lsThe 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 keyHere, 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... PADDINGSo, 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
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.csvBy filtering the outputs on the character set of Base64, we directly keep the only solution.
Author: hellman
License: MIT License
