Safari's latest Technology Preview release introduces support for the "Partitioned" flag in cookies, aligning with the Privacy Sandbox's CHIPS proposal. This development marks a significant step in browser privacy evolution, though its inclusion in Safari's stable release remains pending.
The new partitioned storage feature operates on an opt-in basis, meaning cookies are not automatically partitioned by default. On Safari, while third-party cookies are blocked by default, those with the Partitioned flag receive an exemption from this blocking.
Different browsers handle cookie partitioning in varied ways:
- Safari: Third-party cookies blocked by default, Partitioned flag enables exemption
- Firefox: Partitions cookies by default in strict ETP mode only
- Chrome: Supports Partitioned flag but doesn't enable it by default
How Partitioned Storage Works
Partitioned storage implements a "double-keying" system, where cookie values are partitioned based on two factors:
- The site that set the cookie
- The site the user is currently navigating
For instance, if google.com sets a third-party cookie with the Partitioned flag while a user visits simoahava.com, this cookie value remains accessible only within this specific domain combination. When the user navigates to a different site, such as teamsimmer.com, the cookie cannot be accessed, as it represents a different domain pairing.
This double-keying approach ensures that third-party services can maintain functionality within specific site contexts while preventing cross-site tracking capabilities.
