Final answer:
Identity Providers (IDPs) are responsible for making assertions about identities to service providers in a federated identity service model.
Step-by-step explanation:
In a federated identity service model, the party responsible for making assertions about identities to service providers is known as Identity Providers (IDPs). Identity Providers are trusted entities that provide digital identity services, including authentication and authorization services, to relying parties (RPs) or service providers on behalf of end-users or consuming devices/users (CDUs). These assertions can be in the form of tokens or security assertions that verify the identity and possibly other attributes (like roles or permissions) of a user requesting access to a service provider's resources.