Layering diverse cryptography is a general method to lower the risk of a future, or secret, cryptanalytic attack on a system. This report describes methods to quantifiably estimate this risk reduction.

Diversity is especially helpful in forward security because future attackers have more time to discover new attacks, making attack independence of diverse cryptography the major contribution to risk reduction. Post-quantum security is a part of forward security.

Estimates for highly sensitive data say that the security advantage of diverse layering is worth the extra usage cost, thus advising a decision to layer diverse cryptography.

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