UID Mirroring

What Is UID Mirroring?

UID mirroringUID mirroringAutomatic UID insertion into NDEF messages for trackingView full → is a feature available in NXP NTAG chips that automatically copies the tag's unique identifier (UID) into a specified position within the NDEF message stored on the tag. When a user taps the tag, the scanned URL or text content automatically contains the tag's serial number, enabling per-tag identification and tracking without requiring custom firmware or server-side NFC hardware.

How UID Mirroring Works

The UID mirror feature is controlled through the tag's configuration registers. The tag owner specifies:

1. Mirror position. The byte offset within user memory where the UID should be inserted.
2. Mirror type. UID only, NFC counter only, or both UID and counter.
3. Mirror format. ASCII hex representation of the UID bytes.

When mirroring is enabled, every time the tag is read, the NFC chip dynamically inserts the UID value at the specified offset before transmitting the NDEF messageNDEF messageComplete data unit containing one or more NDEF recordsView full →. The stored URL on the tag contains a placeholder area that gets replaced with the actual UID in ASCII hex format.

For example, a tag programmed with: https://example.com/verify?id=xxxxxxxxxxxxxxxxxx

After mirroring, the reader receives: https://example.com/verify?id=04A23BC1D52A80

Supported Chips

Use Cases

Inventory tracking. Each tag in a deployment reports its unique serial number, allowing a backend system to track which specific tag was scanned, when, and by which device. This is valuable for asset management, product authenticationauthenticationIdentity verification of NFC tags/readers via passwords or cryptographyView full →, and supply chain visibility.

Anti-counterfeiting (basic). While UID mirroring alone does not provide strong anti-cloning protection (UIDs can be read and programmed into clone chips with random UIDs), it adds a basic layer of traceability. For stronger protection, combine UID mirroring with SUN/SDM authentication.

Analytics. Combined with the NFC counter mirror, each scan provides both the tag identity and the total scan count, enabling engagement metrics without requiring server-side session tracking for the count.

Configuration Process

Setting up UID mirroring involves writing to the chip's configuration pages:

1. Write the base NDEF URI with placeholder characters at the mirror position.
2. Set the MIRROR byte in the configuration register to enable UID mirroring.
3. Set the MIRROR_PAGE register to point to the memory page containing the placeholder.
4. Set the MIRROR_BYTE register to specify the byte offset within the page.
5. Optionally set lock bits to prevent configuration tampering.

UID Mirroring vs SDM

UID mirroring provides per-tag identification but not cryptographic authentication. The UID is static, meaning every scan of the same tag produces the same UID value. NTAG DNA chips with Secure Dynamic Messaging go further by generating a unique CMAC signature with every tap, proving the tag is genuine and has not been cloned. For applications where authentication is critical, SDM is strongly preferred over basic UID mirroring.