Forward Secrecy and Cryptographic Agility Questions

Focuses on designing systems that protect long term confidentiality and support safe evolution of cryptographic algorithms. Candidates should explain forward secrecy and how ephemeral key agreement protects past session data against future key compromise, including common constructions such as ephemeral Diffie Hellman and elliptic curve ephemeral Diffie Hellman. The topic includes cryptographic agility practices such as algorithm negotiation, hybrid modes for gradual migration, versioning and rollback strategies, key rotation policies, and emergency re key procedures. Operational considerations cover key hierarchy design, integration with hardware security modules or cloud key management systems, monitoring and alerting for cryptographic operations, audit logging, and testing strategies for algorithm migration including canary rollouts and fallback controls. Candidates should also be able to discuss threat models such as harvest now decrypt later and practical migration paths to quantum resistant algorithms, weighing compatibility performance and operational complexity trade offs.