What is Font Fingerprinting? A Detailed Guide

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Websites often collect information about your device to improve the user experience. While this is true, it is not the whole truth. In reality, websites use this information to uniquely identify and track your browsing habits. Additionally, there is a risk that your device fingerprint could be sold to cybercriminals .

One piece of data that contributes significantly to your browser fingerprint is your device’s fonts. Using font fingerprinting, websites determine how to best serve content to you. But that’s not the only use of font fingerprinting.

This blog explains everything from what font italy number dataset is to the types and techniques used to do it. You will also learn how to bypass font fingerprinting. So, read on to learn more.


What is Font Fingerprinting?
Font fingerprinting is a sneaky technique used by websites and online trackers to identify and track users based on the unique set of fonts installed on their devices. When you visit a website, it scans your device to see which fonts you have installed, without telling you, of course.

By comparing this information against a database of known fonts and their variations, the website can create a unique font fingerprint of you. These profiles are then used for targeted advertising, user tracking, and even more intrusive practices like content censorship or price discrimination.

Font fingerprinting can be quite accurate because most people have a unique combination of fonts installed on their devices. Even if you disable cookies or use private browsing mode, font fingerprinting can still identify you across different sessions.

Font fingerprinting has much greater distinguishing power than other components of a browser fingerprint. The set of fonts installed on your device provides one of the highest entropies —a measure of traceability—to make your fingerprint unique.

Don't just take our word for it, check it out for yourself. Simply visit AmIUnique.org and see a detailed view of your browser fingerprint. Each attribute of the fingerprint has its "similarity index" mentioned, showing what proportion of users have attribute values ​​identical to yours.

The "Source List" attribute usually has an extremely low similarity index compared to other attributes, as shown below.

What is Font Fingerprinting? A Detailed Guide

Due to this distinguishing power, websites keep an eye on you using your system's source list , running hidden scripts right under your nose.


Font Fingerprinting Techniques
Websites perform font fingerprinting by checking the fonts installed on your device. When you visit a website, coding scripts automatically run on the backend to collect information about the fonts your browser can display.

Let’s explore in more detail exactly what techniques websites use for font fingerprinting.


Enumeration of Sources
Font enumeration is the most straightforward approach to font fingerprinting.

It works by using JavaScript to inspect the fonts available on a user's system. When a user visits a website, the website's code is executed inside the browser environment. This code includes instructions to enumerate the fonts, using the FontFaceSet interface or similar methods. Here are the steps involved in this technique:

First, the website begins the enumeration process by calling JavaScript functions designed to ask the browser for installed fonts. The browser responds by providing a list of fonts available for rendering text.

The website then collects this information, often along with other fingerprinting techniques such as canvas fingerprinting or TLS fingerprinting . The collected source data is then transmitted back to the website's server, including the following information:

Font Family, e.g. "Helvetica"

Font Name, e.g. "Helvetica Oblique"

PostScript name, e.g. "HelveticaOblique"

Style, e.g. "Regular"

Sizes


Finally, the website analyzes this font data to create a unique fingerprint for the user's browser. This fingerprint can include details such as the specific combination of fonts installed, their order, and even subtle variations in rendering behavior.


Source Detection
This is a more advanced and quite complex method of font fingerprinting. Instead of directly asking the browser to enumerate the system fonts, this technique performs tests to see if a specific font is installed on the user's system.

Here's how the process works:

The website starts font detection by instructing the browser to render a paragraph of text using the font in question.

After the text is rendered with the specified font, the website measures the size of the rendered text element. This measurement calculates the width and height of the rendered text.

The website compares the rendered text size to a reference size. If the rendered text size matches the reference size, it indicates that the specified font is likely installed on the user's system.