Cryptography and the One-time Pad
A section of the US Digital Millennium Copyright Act (DMCA) forbids decrypting an encrypted copyrighted work if the encryption is designed to “effectively control access” to the work. There are many ways to scramble, or encrypt, data. How do we determine what constitutes “effective” encryption? Let's try out an example. Enter a word or two you'd like encrypted below.
We converted your
phrase to ALL CAPS and removed all but the Latin characters, in order to
simplify our explanations below. Here it is after conversion:
Here are three different encryptions of your text:
Which one of these was obtained using secure (or, as Congress called it, “effective”) encryption? Here are some facts about the methods used. The first one was used very recently to protect electronic documents against unauthorized copying; at least one programmer was jailed in the US for writing code to break it. The second one has been used for millennia. The third one was patented in 1919, but has seen only limited use.
The first method, known as ROT13, simply substitutes for each letter the letter that is 13 steps away from it in the alphabet (looping back from Z to A if necessary). Thus, A becomes N, B becomes O, C becomes P, and so on. As you can see, the protection it offers can be broken by first-graders. As for the copy protection and the jailed programmer? Here's more on the story. Now, which one of these or many other encryption methods did Congress have in mind when in passed the DMCA? What is the standard of effectiveness by which encryption shoud be judged?