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Please consider enabling X25519MLKEM768 for DoH to mitigate “store now, decrypt later” attacks #64

Description

@ScriptKiddie3829

I don't speak English perfectly and asked the AI ​​to write the full text:

Motivation

With the steady advancement of quantum computing, DNS traffic encrypted today using classical key exchange algorithms is potentially vulnerable to "Harvest Now, Decrypt Later" (HNDL) attacks — where adversaries record encrypted traffic now with the intent to decrypt it once sufficiently powerful quantum computers become available.

DNS queries, while short-lived individually, can reveal sensitive information about users' browsing habits and online activity. Protecting this data against future quantum threats is an important step toward long-term privacy.

Proposed Solution

Adding support for the X25519MLKEM768 hybrid key exchange (combining the classical X25519 ECDH with the NIST-standardized ML-KEM-768 post-quantum KEM) would provide protection against HNDL attacks while maintaining compatibility and performance for current clients.

This approach is already gaining traction across the industry and is supported in recent versions of major TLS libraries (e.g., BoringSSL, OpenSSL 3.x with OQS provider).

Precedent

I previously made a similar request to Applied Privacy regarding their DoH resolver — and I'm happy to report that they have since implemented X25519MLKEM768 support. I hope Digitale Gesellschaft will consider following suit, given your organization's strong commitment to digital rights and user privacy.

References

Request

Please consider enabling X25519MLKEM768 in your DoH resolver's TLS configuration to protect users against harvest-now-decrypt-later attacks. Even users who are not currently targeted may benefit from this protection in the long run.

A Personal Note

I am a dissident living under an authoritarian regime. For people in my situation, this is not a theoretical concern — it is a matter of personal safety. State-level adversaries in such countries are known to collect and store encrypted internet traffic at scale, with the clear intention of decrypting it in the future as technology advances. My DNS queries, my browsing patterns, my contacts — all of this, if harvested today and decrypted tomorrow, could put me and others at serious risk.

Privacy-respecting infrastructure like yours is a lifeline for people like me. Post-quantum protection on the transport layer is the next necessary step in making that lifeline truly secure.

Thank you for the important work you do for digital privacy in Switzerland and beyond.

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