A Practical Attack on the MIFARE Classic

TL;DR

This paper presents a practical, low-cost attack on the widely used MIFARE Classic contactless smart card, exploiting cryptographic weaknesses to recover and manipulate secret memory data.

Contribution

It introduces a novel attack method that exploits a weakness in the pseudo-random generator, enabling reading and modifying memory sectors of the card.

Findings

Successfully recovers keystream from the card

Allows reading any memory sector with known block

Enables modification of memory blocks

Abstract

The MIFARE Classic is the most widely used contactless smart card in the market. Its design and implementation details are kept secret by its manufacturer. This paper studies the architecture of the card and the communication protocol between card and reader. Then it gives a practical, low-cost, attack that recovers secret information from the memory of the card. Due to a weakness in the pseudo-random generator, we are able to recover the keystream generated by the CRYPTO1 stream cipher. We exploit the malleability of the stream cipher to read all memory blocks of the first sector of the card. Moreover, we are able to read any sector of the memory of the card, provided that we know one memory block within this sector. Finally, and perhaps more damaging, the same holds for modifying memory blocks.