Can you target a creature with shroud with your own auras?

Shroud is a static ability defined in CR 702.18a: a permanent or player with shroud cannot be the target of spells or abilities. Crucially, this applies to all players equally — there is no exception for the object's owner or controller.

When you cast an Aura spell, it targets the permanent it will enchant as part of its casting (CR 601.2c). Because that targeting step is required, shroud blocks you from legally choosing a creature with shroud as the target, even if it's your own creature.

This is the key difference between shroud and hexproof (CR 702.11a). Hexproof only stops opponents from targeting the permanent, so you can freely attach your own Auras to a creature you control that has hexproof. Shroud has no such restriction — it stops everyone.

Concrete example: You control a Troll Ascetic (which has shroud and regenerate). You want to cast Rancor on it to give it trample. You cannot — Rancor targets when cast, and Troll Ascetic's shroud makes it an illegal target for any player, including you.

Note: If an Aura somehow enters the battlefield attached to a shroud creature without being cast (e.g., via an effect that says "put an Aura onto the battlefield attached to…"), that is not targeting and shroud does not interfere (CR 702.18a only restricts targeting, not attachment by other means).