Illegal Numbers


To understand this blog post, you need to know two things.

  1. There exists a class of numbers which are illegal in some jurisdictions. For example, a number may be copyrighted content, a decryption key, or other text considered illegal.
  2. There exists a class of algorithms which will take any arbitrary data and produce a fixed length text from it. This process is known as “hashing“. These algorithms are deterministic – that is, entering the same data will always produce the same hash.

Let’s take the MD5 hashing algorithm. Feed it any data and it will produce hash with a fixed length of 128 bits. Using an 8 bit alphabet, that’s 16 human-readable characters.

Suppose you live in a country with Lèse-majesté– laws which make it treasonous to insult or threaten the monarch.

There exists a seemingly innocent piece of data – an image, an MP3, a text file – which when fed to MD5 produces these 128 bits: