Why UID2 exists
The digital advertising ecosystem faces a identity crisis:- Third-party cookies are being deprecated
- Mobile ad ID availability is declining
- Privacy regulations require user consent and control
- Privacy by design: Users can opt out at any time
- Transparency: Open-source framework with clear governance
- Interoperability: Works across platforms and partners
- Determinism: Same input always produces the same output
How UID2 works
Token generation
UID2 tokens are generated from personally identifiable information (PII) through a multi-step process:- Input: Email address or phone number
- Normalization: Standardize format (lowercase, trim whitespace)
- Hashing: Apply SHA-256 hash
- Encryption: Encrypt with rotating keys
- Output: UID2 token
- Deterministic (same email always produces the same UID2)
- Encrypted (raw hash is not exposed)
- Refreshable (tokens can be regenerated with new keys)
Token types
| Token Type | Description | Use Case |
|---|---|---|
| UID2 Token | Encrypted, rotatable identifier | Real-time bidding, ad serving |
| Raw UID2 | Underlying identifier before encryption | Secure storage, internal systems |
Key rotation
UID2 tokens are encrypted with keys that rotate periodically. This means:- Tokens eventually expire and must be refreshed
- Compromised tokens become invalid
- Users can effectively reset their identity by regenerating tokens
Privacy features
User opt-out
UID2 includes a centralized opt-out mechanism. When users opt out:- Their UID2 is added to a global opt-out list
- All participants must check this list before using UID2s
- The opt-out persists across all participating companies
Transparency
The UID2 framework is open-source and governed by an independent consortium, providing:- Clear documentation of how identifiers are generated
- Public audit of participating companies
- User-facing explanations of how data is used
No cross-party tracking without consent
UID2 is generated from first-party data (emails collected with consent). It cannot be used to track users who haven’t shared their information with a participating company.UID2 in Narrative
Narrative supports UID2 through automatic generation and native integration with The Trade Desk.Automatic generation
When you upload data with supported identifier types, Narrative can automatically generate UID2 tokens: Supported input attributes:- Hashed Email (any hash algorithm)
- SHA-256 Hashed Email
- Phone Number
- SHA-256 Hashed Phone Number
Trade Desk integration
The Narrative TTD Connector enables seamless UID2 workflows:- Upload data with email or phone identifiers
- Narrative generates UID2 tokens automatically
- Activate audiences directly in The Trade Desk
Existing UID2s
If your data already contains UID2 tokens (from advertising partners or other sources), Narrative’s TTD Connector processes them directly, automatically mapping the UID2 field.UID2 vs. other identifiers
| Aspect | UID2 | Hashed Email | Cookies | MAIDs |
|---|---|---|---|---|
| Persistence | Until opt-out | Permanent | Session/limited | Until reset |
| Cross-device | Yes | Yes | No | No |
| User control | Centralized opt-out | None | Browser settings | Device settings |
| Privacy status | Enhanced | Pseudonymized | Trackable | Pseudo-anonymous |
| Future viability | High | High | Declining | Declining |
Getting started with UID2
To use UID2 in Narrative:- Ensure your data includes email or phone identifiers
- Hash identifiers before upload if not already hashed
- Configure the TTD Connector for your destination
- Narrative handles UID2 generation automatically