Data & identity · also called UID2, Unified ID 2.0
Unified ID 2.0 (UID2)
Unified ID 2.0 (UID2) is an open-source advertising identifier, originally developed by The Trade Desk, generated from a user's hashed and salted email address or phone number with their consent.
UID2 aims to replace third-party cookies with an identifier based on something people already give publishers when they log in: an email address or phone number. The address is normalised, hashed and salted, then turned into an encrypted token that rotates regularly. Publishers pass the token in bid requests, and authorised buyers can decrypt it into the underlying UID2 to recognise the same user across sites, apps and CTV.
The framework was initiated by The Trade Desk and released as open-source, with other companies acting as operators and participants. Users are supposed to be told about UID2 and can opt out through a central portal, which is honoured across participants. A sister framework, European Unified ID, is designed for Europe's consent rules.
UID2 is pseudonymous, not anonymous: it is derived from personal data and can link activity, so laws like GDPR, CCPA / CPRA and DPDP still apply. Its reach depends on how many people log in, which is why publishers push registration. Critics also point out that a widely shared persistent ID can recreate some of the tracking concerns of cookies.
Think of it like this
UID2 is like wearing a numbered wristband at a festival that is derived from your ticket but does not show your name; every stall that is part of the scheme can recognise the wristband.
An example
A US news publisher requires free registration for some articles; 20% of its readers log in, and their hashed emails become UID2 tokens in bid requests, which earn noticeably higher CPMs than anonymous impressions.
Related terms
European Unified ID (EUID)
European Unified ID (EUID) is the European version of Unified ID 2.0, an email-based, hashed and encrypted advertising identifier designed to work within GDPR's consent requirements.
Hashed email
A hashed email is an email address transformed by a one-way cryptographic function, usually SHA-256, into a fixed string used to match users across systems without sharing the plain address.
RampID
RampID is LiveRamp's pseudonymous, people-based identifier, which links a person's or household's online and offline identifiers so advertisers and publishers can match audiences without sharing raw personal data.
Deterministic matching
Deterministic matching links identifiers to the same person using definite, shared information, such as the same login email or phone number, rather than statistical inference.
Cookieless advertising
Cookieless advertising means targeting and measuring ads without third-party cookies, using approaches like first-party data, contextual targeting, alternative IDs, clean rooms and modelled measurement.
Sources: Unified ID 2.0