Preventing quantum downgrade attacks against IPsec
Sep 29, 2026Christopher Patton, Amos Paul, Lina Baquero
Summary
This post details the development and implementation of a mitigation against quantum downgrade attacks on IPsec. It explains the vulnerability in IPsec's IKEv2 protocol that allows attackers to trick endpoints into using weaker classical cryptography by manipulating handshake messages. The post introduces an IETF extension that adds a downgrade protection mechanism to IPsec, ensuring that both parties support post-quantum cryptography. Cloudflare has implemented beta support for this extension in its IPsec products (WAN, Magic Transit) and encourages ecosystem adoption.
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