This whitepaper gives a short inside of hacking Mifare Classic. Mifare Classic is a inexpensive, entry-level chip, based on ISO/IEC 14443 Type A, 1kB or 4kB. It uses the 13.56 Mhz contactless smartcard standard, proprietary CRYPTO1 with 48 bits keys. There is no protection against cloning or modifications. Anyone with 50 EUR reading can use this weakness against their infrastructure. This cookbook is a proof of concept demonstrating how easy it can be done.
You can download it from the following link: https://packetstormsecurity.com/files/download/103638/cooking-with-mifare-classic-PS.pdf
Source: https://packetstormsecurity.com/files/103638/Cooking-With-Mifare-Classic.html