Step by Step Explanation:

Digital signatures provide non-repudiation, ensuring that the sender cannot deny signing a transaction. This mechanism ties the transaction to the entity through cryptographic assurance.

Federation involves identity management and authentication but does not address non-repudiation.

Key escrow is used for securely storing encryption keys and is unrelated to transaction agreements.

Salting hashes enhances password security but does not support transactional non-repudiation.