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Originally posted 2022-07-09. Last updated 2022-08-06.
This is an expanded version of a microblog entry:
Stylometric fingerprinting resistance.
It contains everything in that entry and more.
Following a recent landmark SCOTUS ruling, many have been trying to publish resources to help people find reproductive healthcare. They often wish to publish anonymously, to avoid being harassed or doxxed by overzealous religious fundamentalists. Some people asked me for help.
There’s no shortage of guides on how to stay anonymous online. I recommend using the Tor Browser in a disposable Whonix VM. The Whonix Wiki has a good guide to anonymous publishing:
Few guides cover stylometric fingerprinting.
Stylometric fingerprinting analyzes unique writing style (i.e., it uses stylometry) to identify the author of a work. It’s one of the most common techniques for de-anonymization, used by adversaries ranging from trolls to law enforcement.
For a TL;DR, skip to the “Conclusion” section.
To paint with a broad brush, we can divide stylometric fingerprinting into machine- and human-driven techniques.
Common advice is to use offline machine translation to translate works to and from another language. Two options that come to mind:
This paper shows that machine translation alone isn’t nearly as strong a method as manual approaches:
Adversarial stylometry: Circumventing authorship recognition to preserve privacy and anonymity
Manual approaches include obfuscation (hiding your writing style) or imitation (mimicking another author). These approaches have excellent success rates, even among amateur writers. The aforementioned Whonix wiki page lists common stylometric fingerprinting vectors for manual approaches to address.
Limiting unusual vocabulary and sentence structure make for a good start. Using a comprehensive and highly-opinionated style-guide should also help. The Economist has a good one that was specifically written to make all authors sound the same:
The Economist Style Guide, 12th edition (application/pdf)
Nearly every respected newspaper has a style guide. Tech companies typically publish or use a style guide for technical writing. I’m a fan of Red Hat’s style guide:
Red Hat Technical Writing Style Guide, Edition 5.1.
Good style guides are long, and learning one is tough. Read a large amount of conforming content to help yourself internalize a guide’s rules.
The reading difficulty of a piece is a coarse but extremely simple measure. If the anonymous author of a piece writes at a tenth-grade level, their other writings are likely near a tenth-grade level too.
Check your content’s reading level using common readability metrics. The Flesch-Kincaid Grade Level is one of the most popular. If you write at a given grade level, publish anonymously at a lower grade level. I recommend using a lower grade level rather than a higher one for two reasons:
1. Artificially inflating the reading level generally produces cringeworthy writing.
2. Writing at a lower level carries less risk of introducing uncommon fingerprintable words.
For any inexperienced writers: opinionated offline grammar checkers may supplement a manual approach by normalizing any distinguishing “errors” in your language. Two of my favorites:
That being said, nothing beats a human editor. Find someone you trust to review your work.
Here are some resources for further reading:
"How we authenticate a document" by OrphAnalytics SA.
"Unveiling the Anonymous Author: Stylometry Techniques" by SerHack.
Human-driven techniques were behind the most high-profile successful cases of stylometric fingerprinting by law enforcement. When the Unabomber published his manifesto, his brother recognized some signature phrases in his manifesto and went to the FBI. One of the largest Australian CSA cases involved recognizing someone’s distinctive greeting of “Hiya”:
Australian Womens' Weekly: The online CSA epidemic
While the research I cited seems to indicate that machine translation is a poor way to thwart machine-driven techniques, I’m not convinced that it’s useless. Machine translation may be ineffective at thwarting machine-driven stylometric fingerprinting, but it should be able to highlight or remove uniqueness a human could notice. Let’s look at some examples.
Here’s a sentence from the Unabomber manifesto:
But it is obvious that modern leftist philosophers are not simply cool-headed logicians systematically analyzing the foundations of knowledge.
David Kaczynski noticed the phrase “cool-headed logicians” as a potential signature identifying his brother. After further analysis, the author was clear.
After I read the first few pages, my jaw literally dropped. One particular phrase disturbed me. It said modern philosophers were not “cool-headed logicians.” Ted had once said I was not a “cool-headed logician,” and I had never heard anyone else use that phrase…We had Linda’s childhood friend Susan Swanson, a private investigator, take two of Ted’s letters to a linguistics expert, who analyzed them and found there was an 80 percent chance the same person had written the letters and the manifesto.
Let’s run it through Argos Open Translate’s English-Esperanto filter, and then translate it back to English:
But it is evident that modern left-wing philosophers are not simply dehydrated logicians systematically analyzing the foundations of knowledge.
“Dehydrated logicians” obviously isn’t the correct term to use. The fact that the translation algorithm mistook “cool-headed” for “dehydrated” indicates that “cool-headed” was an unusual choice of words to use in this context, and therefore a fingerprinting vector. A more common phrase like “detached” would be safer.
(I didn't pick Esperanto for any particular reason)
Let’s look at another phrase:
Whoohoo! It’s a-me, Mario!
“Mario” is a common name, but I have a feeling you know that this “Mario” is the Nintendo character. Running this line through an English-Esperanto and Esperanto-English filter gives us:
Who! It’s me, Mary!
Our findings:
Additionally, inflection (e.g., using an exclamation point) can make your writing voice recognizable. Use it with care.
Let’s re-phrase Mario’s line to be less identifiable:
Hey, it’s me. Mario.
That’s a little better.
I have my share of fingerprintable stylistic and formatting quirks. A non-exhaustive list:
Developing a high-quality writing style is hard. Developing and switching between multiple different styles is even harder. It takes time to master multiple style guides, cultivate a different "voice" free of your usual idiosyncrasies, and keep your different voices from influencing one another. "Getting into character" won't happen overnight if you don't have experience.
Translation tools are training-wheels to help you learn to identify idiosyncrasies. As you get better, you might be able to filter out problematic language without their help.
Don't feel pressured to start soon! If you want to publish under a truly anonymous pseudonym, you should first hone your craft. Alternatively, find a good editor (I am not the best person for this job, sorry).
If you wish to write anonymously, I recommend the following:
1. Analyze your non-anonymous writing, looking for patterns. Write these patterns down. When you review your anonymous publications, refer to your list of identifiable patterns and remove them. Consider asking someone else for help, since your own bias might cause you to overlook some patterns.
2. Translate your work to and from another language with an offline machine translator. Don’t actually publish the translator’s output; instead, read the output to identify potentially-fingerprintable language you missed in the previous step.
3. Correct any grammatical or spelling errors; mistakes you make might be unique.
4. Conform to an opinionated style-guide that you don’t normally use in your other writing.
5. If, after doing the prior steps, your anonymous work still has a reading level too similar to your non-anonymous writing: reduce the reading level by choosing simpler words.
More information about stylometric fingerprinting resistance is on the Hitchiker's Guide to Online Anonymity:
HGOA Appendix A4: counteracting forensic linguistics
Stay safe, everyone.
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Copyright © 2021 Rohan Kumar