MIFARE Classic Access Bits Calculator
Interactive MIFARE Classic 1K/4K sector trailer access bits calculator. Set C1/C2/C3 permissions for data blocks and sector trailer, get real-time hex bytes 6-9. Also works in reverse — decode existing access bytes back to human-readable permissions. Essential for MIFARE Classic card programming and key management.
Set Permissions per Block
Each block's C1/C2/C3 bits control read/write/increment/decrement/transfer/restore.
Sector Trailer (Block 3) Access
Sector Trailer Bytes 6-9 (Hex)
Byte 6: ~C23 ~C22 ~C21 ~C20 ~C13 ~C12 ~C11 ~C10 (bit-inverted: ~C1x, ~C2x, ~C3x)
Byte 7: C13 C12 C11 C10 ~C33 ~C32 ~C31 ~C30 (C1x + bit-inverted ~C3x)
Byte 8: C33 C32 C31 C30 C23 C22 C21 C20 (C3x + C2x)
Byte 9: (user data — typically 0x00)
How to Use This Calculator
Build mode: Select access permissions for each block, get the resulting sector trailer bytes in real time. Use this when programming new MIFARE Classic cards — the bytes 6-9 you see here go directly into the sector trailer.
Decode mode: Paste existing bytes 6-9 from a sector trailer, see human-readable permissions. Use this when reverse-engineering existing MIFARE cards or debugging access issues.
Key concept: MIFARE Classic stores each permission bit twice — once normal, once inverted. If the normal and inverted bits don't match, the card treats the block as inaccessible (blocked forever). This calculator always generates valid, self-consistent access bits.
Example Use Cases
- NFC access control: Set sectors as read-only after writing UID/access data, preventing tampering
- Value blocks (e-wallet): Configure blocks for increment/decrement operations with Key B write protection
- NDEF on MIFARE Classic: Configure the NDEF data sector with appropriate read/write permissions
- Transport configuration: Understand the default "FF 07 80" access bytes found on new cards
- Card cloning analysis: Decode unknown sector trailers to understand the original card's security model
Related Tools
NFC Tag Capacity Calculator — Compare MIFARE Classic vs NTAG vs DESFire memory | NDEF Message Parser — Decode NDEF content from MIFARE cards | APDU Command Builder — Build APDUs for MIFARE reader commands