Preventing quantum downgrade attacks against IPsec

What happened

A sophisticated attacker with a quantum computer can exploit a protocol design flaw to downgrade post-quantum IPsec tunnels to classical crypto. For Birthday Week, Cloudflare is helping one of the Internet’s core security protocols develop stronger protections against quantum downgrade attacks.

The world is racing to build the first generation of quantum computers. The need for backwards compatibility creates its own risk.

In a downgrade attack , an on-path attacker between a client and server tricks the endpoints into using weaker crypto than they support. It does so by manipulating the messages sent between client and server, making it appear to one party that its peer does not support PQ at all.