IDN Homograph Detector

The IDN Homograph Detector is a Python script used to detect homograph attacks of Internationalized Domain Names (IDNs). A write-up covering the concept of this script can be found at my blog at intothethickof.it.

The script uses a mapping of Unicode characters that are visually-similar to Latin letters and a list of keywords to check to detect possible IDN homograph attacks.

Some use-cases include:

• Raising awareness of IDN homograph attacks
• Monitoring of newly registered domains to detect IDN homograph attacks of your company/brand

Requirements

1. The script was developed in Python 3.10.5 and requires the idna library which can be installed using pip:

pip install idna

2. The script takes in as input a dictionary file (.txt file) which contains a mapping of Latin letters to visually-similar Unicode characters in their Hex values. The contents of the dictionary file should look like this:

a|0251|03B1|0430|203|...
b|13CF|1472|15AF|...
c|1D04|2CA5|0441|1043D|188|107...
.
.
.
x|0445|1541|157D|1E8D|3C7|...
y|0263|028F|03B3|0443|04AF|...
z|1D22|17A|17C|1E95|17E|...

3. The script takes in as input a text file of keywords to monitor. Each keyword should be separated by a new line. The contents of the file should look like this:

google
facebook
youtube
twitter
instagram
linkedin
apple
microsoft
...

4. The script takes in a text file of punycode domains to check. Each punycode domain should be separated by a new line. The contents of the file should look like this:

xn----ktbjphfiq9e1a.xn--p1acf
xn--65-1lc3f.xn--p1ai
xn--j1ai0c.com
xn--j1ai0c.store
xn--j1aij3c.xn--p1acf
xn--h1af0dg.xn--d1acj3b
xn--h1ahgigg2f.top
...

The contents of the dictionary can be adjusted depending on what is visually-similar to you. The input files will affect the output of the script and the amount of time/resources to complete the script as it will increase/decrease the number of possible IDN homographs. A free list of newly registered domains can be obtained from WhoisDS.

Usage

To run the script:

python idn_homograph_detector.py <dictionary_file> <keyword_file> <punycode_domains_file>

The script will output detected IDN homographs by printing the results to your console and saving them to a text file named detected_homograph.txt.

For example, the console will look like this:

The detected_homograph.txt file will look like this:

Disclaimer

THIS SCRIPT IS FOR EDUCATIONAL AND INFORMATIONAL PURPOSES ONLY. THE AUTHOR DOES NOT TAKE RESPONSIBILITY FOR ANY MISUSE, LOSS, OR DAMAGE CAUSED BY THE USE OF THIS SCRIPT.