Permalock

Permalock

Permalock is a permanent, irreversible memory protection feature defined in the EPC Gen2 standard. Once a Permalock command is applied to a memory block, that block can never be written again — not even by a reader presenting the correct Access Password. Permalock provides the strongest possible data integrity guarantee for RFID tag memory, ensuring that critical information remains immutable throughout the tagged object's lifecycle.

How Permalock Differs from Lock

epc-gen2/" class="glossary-term-link" data-term="EPC Gen2" data-definition="UHF RFID air interface standard." data-category="Standards & Protocols">EPC Gen2 defines two levels of write protection:

Lock is suitable for scenarios where data may need to be updated later — for example, a logistics company that locks the EPC Memory during shipment but unlocks it at the destination for re-encoding. Permalock is for data that must never change under any circumstances.

Use Cases

Aviation component tracking: ATA Spec 2000 requires that RFID tags on aircraft parts carry immutable identification data. The part number and manufacturer code in User Memory are permalocked at the factory. Maintenance data appended to subsequent memory blocks may be locked (reversible) to allow authorised updates during service events.

Pharmaceutical serialization: Under FDA DSCSA requirements, the SGTIN encoded on pharmaceutical packaging must not be alterable after commissioning. Permalocking the EPC memory bank ensures that the drug's identity cannot be tampered with during distribution.

Anti-counterfeiting: Permalocking the TID Memory extension area (where supported) and the EPC bank prevents attackers from overwriting tag identity data. Combined with tag authentication using crypto suite algorithms, permalocked tags provide strong physical-digital binding.

Implementation Considerations

Permalock is supported by most modern tag ICs, but the granularity varies. Some chips support per-word permalocking of User Memory, allowing a staged approach where different supply chain partners can each write and permalock their own data sections while leaving subsequent sections open. Others support only per-bank permalocking.

Before executing a Permalock command, the system must:

1. Verify the data is correct (read-after-write verification)
2. Confirm the Access Password is securely stored for future read access
3. Ensure no subsequent process requires modifying the locked data

Mistakes are permanent. A tag with incorrectly permalocked data must be physically replaced — there is no software recovery path. Production systems should implement multi-step confirmation workflows and pre-lock validation checks to prevent costly errors.