Mifare card memory space?

Question

What is the net memory space remaining in a MIFARE Classic 1K card considering that keys and access bits take 16 bytes per sector, and the unique id (UID) and manufacturer data takes 16 bytes for each card?

Answer 1

MIFARE Classic 1K consists of 16 sectors. One sector consists of 4 blocks (sector trailer + 3 data blocks). Each block consists of 16 bytes.

This gives 16 Sectors * 4 Blocks * 16 Bytes = 1024 Bytes.

The actually usable data area depends on how you want to use the card:

1. You use only one key per sector (key A); you use the unused parts of the sector trailers for data storage; you don't use a MIFARE application directory (MAD):

   • The first block of the first sector is always reserved (UID/manufacturer data) and cannot be used to store user data.
   • 6 bytes of each sector trailer are reserved for key A. 3 bytes of each sector trailer are reserved for the access conditions. The remaining 7 bytes of the sector trailer can be used to store user data.

   Thus, you can store 1 Sector * (2 Blocks * 16 Bytes + 1 Block * 7 Bytes) + 15 Blocks * (3 Blocks * 16 Bytes + 1 Block * 7 Bytes) = 864 Bytes.

2. You use two keys per sector (key A and key B); you use the unused parts of the sector trailers for data storage; you don't use a MIFARE application directory (MAD):

   • 12 bytes of each sector trailer are reserved for key A and B. 3 bytes of each sector trailer are reserved for the access conditions. The remaining byte of the sector trailer can be used to store user data.

   Thus, you can store 1 Sector * (2 Blocks * 16 Bytes + 1 Block * 1 Byte) + 15 Blocks * (3 Blocks * 16 Bytes + 1 Block * 1 Byte) = 768 Bytes.

3. You use two keys per sector (key A and key B); you don't use the unused parts of the sector trailers for data storage; you don't use a MIFARE application directory (MAD):

   Thus, you can store 1 Sector * 2 Blocks * 16 Bytes + 15 Blocks * 3 Blocks * 16 Bytes = 752 Bytes.

4. You use two keys per sector (key A and key B); you use the unused parts of the sector trailers for data storage; you use a MIFARE application directory (MAD):

   • The data blocks and the general purpose byte (remaining byte in the sector trailer) of the first sector are reserved for the MAD.
   • The general purpose byte in the other sectors can be used.

   Thus, you can store 15 Blocks * (3 Blocks * 16 Bytes + 1 Block * 1 Byte) = 735 Bytes.

5. You use two keys per sector (key A and key B); you use NXP's NDEF data mapping to transport an NDEF message:

   • The MAD is used to assign sectors to the NDEF application.
   • NDEF data can only be stored in the 3 data blocks of each NDEF sector.
   • The NDEF message is wrapped in an NDEF TLV structure (1 byte for the tag 0x03, three bytes to indicate a length of more than 254 bytes).

   Thus, you can store an NDEF message of up to 15 Blocks * 3 Blocks * 16 Bytes - 4 bytes = 716 Bytes. Such an NDEF message could have a maximum payload of 716 Bytes - 1 Byte - 1 Byte - 4 Bytes = 710 Bytes (when using a NDEF record with TNF unknown, 1 header byte, 1 type length byte, 4 payload length bytes).