MIFARE Classic 4K Card

What a MIFARE Classic 4K card is

A MIFARE Classic 4K card is a 13.56 MHz ISO/IEC 14443 Type A card built on NXP’s MIFARE Classic 4K chip, the S70; the current part is the Classic EV1 4K, MF1S70. Apart from memory, the SAK and ATQA values and NXP’s originality check (1K only), it shares the 1K’s command set, two keys per sector, UID options and Crypto-1 cipher, all explained on the MIFARE Classic card page. What the 4K adds is memory: 40 sectors instead of 16, four times the bytes.

When 4K memory is really needed

A door or hotel credential uses only a few blocks, and a 4K adds no security, so 1K is the default. A 4K is worth specifying when the system names S70, or when sectors rather than bytes run out:

• Several independent applications, each with its own keys. Classic sets keys per sector, so each application takes whole sectors. Under NXP’s MIFARE Application Directory a 1K has room for 15 application sectors and a 4K for 38, with sector 16 holding the extended directory.
• Records kept on the card. Transaction logs, visit histories or several ticket products stored on the card itself can need more than the 1K’s 752 bytes; one large 4K sector alone holds 240 bytes.
• An existing specification that names S70 or MF1S70. Order the chip the system was built for; a 1K is not a substitute.

Two cautions. A system written for the 1K directory (MAD1) can use a 4K card with the extended directory (MAD2) without changes, but, as NXP’s application note says, it then reaches only the lower 1K. And if the extra memory is meant for several parties sharing one card securely, a 4K Classic gives each of them more room but not more protection: MIFARE DESFire, with separate AES-keyed applications, or MIFARE Plus, in 2 KB or 4 KB with AES in security level 3, are the secure multi-application options.

4K memory layout: 32 small and 8 large sectors

NXP organises the 4096-byte EEPROM as 32 sectors of 4 blocks followed by 8 sectors of 16 blocks, 40 sectors in all, with 16-byte blocks throughout. The small sectors repeat the 1K layout; the large ones are what make a 4K different to program.

• The trailer moves. The sector trailer is block 3 in sectors 0–31 and block 15 in sectors 32–39, so issuing software must not assume that every fourth block is a trailer.
• Access bits cover groups in the large sectors. In sectors 32–39 each set of access bits applies to five data blocks at once (blocks 0–4, 5–9 and 10–14 of the sector), so data that needs different permissions goes into a different group or sector.
• The whole block-address range is used. Block addresses are one byte, 00h to FFh; the large sectors start at block 128 (80h).
• Same key format. Every sector’s last block holds Key A, the access bits, a general-purpose byte and Key B in the same 16-byte format as the 1K, and cards arrive in the same transport configuration.

A reader tells a 4K from a 1K by the SAK it returns on selection: 18h for the 4K, 08h for the 1K. The ATQA shows the UID length: 0042h for the 7-byte UID version of the 4K and 0002h for the 4-byte NUID version.

MIFARE Classic EV1 4K (MF1S70)

Our 4K cards use the genuine NXP part in production today, the MIFARE Classic EV1 4K from the MF1S70 family; we do not substitute a compatible chip. What EV1 changed in both sizes is set out on the MIFARE Classic card page. These are the 4K-specific points from NXP’s MF1S70 datasheet:

A system that relies on NXP’s originality check to confirm genuine chips cannot apply it to 4K EV1 cards. For the 4K, the assurance is the NXP part number the supplier states on the order; a sample test in the real system shows that the card works, not that the chip is genuine. The MIFARE Classic card page explains the “MIFARE-compatible” chips with published backdoor keys that make this matter, and why we build on NXP EV1 instead.

Security and UID: the same as the 1K

The 4K uses the same broken Crypto-1 cipher as the 1K, EV1 included, so it can be copied just as easily; more memory adds no protection. The security analysis, the choice between a 4-byte and a 7-byte UID and the measures that limit risk on an installed Classic system are explained on the MIFARE Classic card page. For new secure systems NXP refers customers to MIFARE DESFire and MIFARE Plus.

Formats, printing and encoding

The S70 chip goes into the same formats as the 1K: ID-1 cards in PVC, PET-G or wood, key fobs, silicone wristbands and MIFARE stickers. Printing and numbering options are those listed for the MIFARE Classic card, and numbered 4K cards come with a file (Excel, CSV or XML) tying each UID to the printed number. For encoding through our RFID encoding service, send the map of all 40 sectors, including which of sectors 32–39 are used and how their access-bit groups are set. We verify every encoded 4K card by reading it back, and a data report accompanies each encoded order. Whether we load your keys is agreed in the quotation, as is any key handover.

S70 wood card

A wood card body with a MIFARE Classic 4K chip.

S70 silicone wristband

A wearable MIFARE Classic 4K credential for hotels, gyms and water parks.

S70 key fob

The same chip in a key fob for access systems.

Ordering MIFARE Classic 4K cards

We make MIFARE Classic 4K cards, fobs, wristbands and stickers with genuine NXP S70 chips, printed and personalised to your specification. Send the chip (S70 with a 4-byte or 7-byte UID), format, artwork, encoding requirement and quantity through the inquiry form, by email or on WhatsApp, and test a sample in your readers before the order. We do not supply access-control readers, locks or software, and we do not duplicate cards from systems the buyer does not administer. Related choices: MIFARE Classic card, MIFARE Plus card, MIFARE DESFire EV2 cards, hotel key cards and all RFID cards.

Technical reference: NXP MIFARE Classic EV1 4K datasheet (MF1S70YYX_V1), MIFARE Application Directory note AN10787 and MIFARE Classic product page. Chip documentation describes IC capabilities; it does not establish stock or a finished card’s compatibility with your system.