The prime number that was declared illegal
In 2001, a prime number was discovered that doubled as an executable computer program. When written out as a binary file, this specific prime number decoded into DeCSS, a program that bypassed DVD copy protection. Because distributing DeCSS was deemed illegal under the Digital Millennium Copyright Act, possessing or publishing this exact mathematical prime number became a legal gray area, highlighting a bizarre clash between math and copyright law.
The Equivalence of Data and Numbers
Every digital file stored on a computer—whether an image, a text document, an audio recording, or a software program—is fundamentally an ordered sequence of binary digits: ones and zeros. When interpreted in base two, any such sequence represents a single, specific positive integer. For example, a three-byte text snippet corresponds to a 24-bit binary number, which can be expressed in ordinary base-ten decimal notation. In computer science and mathematical logic, this concept is closely related to Gödel numbering, a framework showing that any formal statement or algorithm can be encoded uniquely as a natural number.
Under ordinary conditions, people do not treat digital files as numbers; they treat them as functional software, media, or documents. However, because mathematical integers can have distinct properties—such as primality, where a number is divisible only by one and itself—a digital file can theoretically possess intrinsic mathematical identities. In 2001, software developer and mathematician Phil Carmody set out to demonstrate what happens when legal restrictions on distributing specific software code intersect with the mathematical reality of numbers.
The Rise of DeCSS and the DMCA
In the late 1990s, commercial movie DVDs were encrypted using a proprietary scheme called the Content Scramble System, or CSS. CSS was intended to prevent unauthorized copying and ensure DVDs could only be played on licensed hardware or approved software players. In 1999, a group of programmers reverse-engineered the CSS algorithm and published DeCSS, a small computer program capable of decrypting the contents of CSS-protected DVDs. This allowed DVD playback on unsupported platforms like Linux, but it also enabled users to extract raw video data without authorization.