This is a good short lesson in public key cryptography. We also learn why a particular prime number that starts with 85650789657397829 and has 1402 more digits is an illegal number. If you have a DVD player, you are in possession of the number.
Wikipedia: "One of the earliest illegal prime numbers was generated in March 2001 by Phil Carmody. Its binary representation corresponds to a compressed version of the C source code of a computer program implementing the DeCSS decryption algorithm, which can be used by a computer to circumvent a DVD's copy protection."