The Content Scrambling System (or Content Scramble System) is a system to encrypt and copy-protect DVDs. Such systems are generally called Digital Rights Management (or DRM) systems. CSS uses symmetric cryptography. It was introduced in 1996; today, it is considered ineffective.

In October 1999, Jon Lech Johansen and two other people (who remained anonymous) broke the system. CSS uses 40-bit cryptographic keys; because of different design problems, the effective key length is only about 16 bits. A 450 MHz processor, current at the time could brute force crack this in less than a minute. A modern processor such as the Core i7 or Athlon 64 can crack it in a few seconds.