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Sapphire tickets

Theory

Sapphire tickets are similar to Diamond tickets in the way the ticket is not forged, but instead based on a legitimate one obtained after a request. The difference lays in how the PAC is modified. The Diamond ticket approach modifies the legitimate PAC to add some privileged groups (or replace it with a fully-forged one). In the Sapphire ticket approach, the PAC of another powerful user is obtained through an S4U2self+u2u trick. This PAC then replaces the one featured in the legitimate ticket. The resulting ticket is an assembly of legitimate elements, and follows a standard ticket request, which makes it the most difficult silver/golden ticket variant to detect.

Practice

Since Diamond tickets modify PACs on-the-fly to include arbitrary group IDs, chances are some detection software are (of will be) able to detect discrepancies between a PAC's values and actual AD relationships (e.g. a PAC indicates a user belongs to some groups when in fact it doesn't).
Sapphire tickets are an alternative to obtaining similar tickets in a stealthier way, by including a legitimate powerful user's PAC in the ticket. There will be no discrepancy anymore between what's in the PAC and what's in Active Directory.
The powerful user's PAC can be obtained through an S4U2self+u2u trick.
UNIX-like
Windows
From UNIX-like systems, Impacket's ticketer (Python) script can be used for such purposes with the -impersonate argument.
As of September 25th, 2022, this feature is in a pull request (#1411) awaiting to be merged.
The arguments used to customize the PAC will be ignored (-groups, -user-id, -extra-sid,-duration), the required domain SID (-domain-sid) as well as the username supplied in the positional argument (baduser in this case). All these information will be kept as-is from the PAC obtained beforehand using the S4U2self+u2u trick.
ticketer.py -request -impersonate 'domainadmin' -domain 'DOMAIN.FQDN' -user 'domain_user' -password 'password' -aesKey 'krbtgt/service AES key' -domain-sid 'S-1-5-21-...' 'baduser'
At the time of writing this recipe, September 25th, 2022, no equivalent exists for Windows systems.