In short: secure attribution is “whodunit?!” in cyberspace.
Secure attribution is strongly related to making and proving statements. A controller makes statements to the a validator or verifier, who in turn validates the statements issued. A controller “owns” the statement: content and attribution via digital signatures.
Secure attribution of a statement is a way of proving that the statement is an authentic statement of the controller. In the context of KERI and ACDC secure means a Validator may cryptographically verify the statement.