RC4 was introduced in 1987 and its algorithm was a trade secret. In 1994, a description of its algorithm was anonymously posted in a mailing group.http://en.wikipedia.org/wiki/RC4
MIFARE Classic is a contactless smartcard that was widely used in Europe. It used a set of proprietary protocols/algorithms. However, they were reverse-engineered in 2007. It turned out that the encryption algorithms were weak (using only 48bits) and thus breakable. (new version employs stronger crypto. Surprisingly, the vulnerable old version still in use, likely in your wallet right now) http://en.wikipedia.org/wiki/MIFARE
