Tatsu Signing Server

The Tatsu Signing Server (TSS) is a service provided by Apple. Apple provides a list of available services at gs.apple.com. There is an Apple internal equivalent, known as Spidercab, running at tatsu-tss-internal.apple.com which is accessible only within Apple's VPN. Spidercab is used to sign internal/debug builds of iOS, including old versions that are no longer signed on production.