Mifare Classic Card Recovery Tool Hot ((new)) -

Such tools are for only. Using them without permission on cards you don’t own/operate may be illegal.

Configure Mifare Card Encryption and Reading - Akuvox Knowledge Base

In 2008, researchers Karsten Nohl and Henryk Plötz reverse-engineered the proprietary Crypto-1 stream cipher. They demonstrated that if you could capture a few encrypted authentication attempts, you could crack the 48-bit key in under a minute on a standard PC.