The Fudan 4K​ (model FM11RF32/34/40​ series) is a high-frequency (HF) contactless RFID chip​ developed by Shanghai Fudan Microelectronics. It is a fully compatible, cost-effective replacement for the MIFARE Classic 4K (S70)​ chip, offering enhanced memory capacity for applications requiring more storage.

1. Core Definition

The Fudan 4K is a 13.56 MHz read/write integrated circuit that operates according to the ISO/IEC 14443-A standard. It is designed as a pin‑to‑pin and command‑set compatible​ alternative to the NXP MIFARE Classic 4K, enabling seamless integration with existing MIFARE Classic infrastructure. The chip provides 4 KB of EEPROM​ and uses the same proprietary Crypto1 security scheme as the MIFARE Classic family.

2. Key Technical Specifications

3. Protocol & Compatibility

• MIFARE Classic 4K (S70) Compatible: Fully emulates the memory organization, command set, and authentication protocol of the original NXP chip. Existing MIFARE Classic 4K readers can operate with Fudan 4K cards without any modification.
• ISO/IEC 14443‑A: Compliant with the international standard for proximity cards.

4. Memory Layout Details

The 4 KB memory is divided into two types of sectors:

• Small Sectors (0–31): 4 blocks per sector (64 bytes per sector). Each sector’s last block is the Sector Trailer​ containing the two 6‑byte keys (Key A, Key B) and access bits.
• Large Sectors (32–39): 16 blocks per sector (256 bytes per sector). Similarly, the last block of each large sector is the Sector Trailer.

This structure allows flexible data storage, with each sector protected by independent Crypto1 keys.

5. Common Applications

• High‑Capacity Access Control: Systems requiring multiple credentials or extended user data.
• Public Transportation: Metro, bus, and taxi cards that need to store journey history or multiple fare tables.
• Campus/Enterprise Multi‑Application Cards: Integrated cards for ID, library, canteen, parking, and small‑value payment.
• Loyalty & Stored‑Value Systems: Prepaid cards with higher transaction‑log capacity.

6. Security Note

Like the MIFARE Classic 1K/4K family, the Fudan 4K employs the Crypto1 cipher, which is known to be cryptographically broken. Cards can be cloned or keys recovered using tools such as Proxmark3​ or ChameleonMini. Therefore, it is not recommended for high‑security or high‑value applications​ unless supplemented with additional security layers (e.g., online validation, dynamic data).

7. Advantages

• Cost‑Effective: Significantly cheaper than original NXP MIFARE Classic 4K chips.
• Drop‑in Replacement: No hardware or software changes required in existing MIFARE Classic 4K systems.
• Large Memory: 4 KB capacity suits applications that need to store more data than the 1 KB version.

Summary

The Fudan 4K is a high‑capacity, economically attractive alternative to the MIFARE Classic 4K, offering full compatibility and 4 KB of storage for medium‑security RFID applications in access control, transportation, and multi‑purpose card systems. Its main limitation is the inherited Crypto1 security weakness, which should be considered when deploying it in sensitive environments.