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Firefox intermittently failing Cloudflare PQC X25519MLKEM768 test

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  • Last reply by TyDraniu
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Hello,

I have been testing all browsers I use (Firefox, Chrome, Edge) on Cloudflare Post-Quantum Key Agreement to verify PQC support. They all support the X25519MLKEM768 hybrid scheme (i.e. Cloudflare web page returns "You are using X25519MLKEM768 which is post-quantum secure").

The issue: When I run the test in Firefox multiple times by doing repeated hard refreshes (Ctrl+Shift+R), quite often the result is "You are using X25519 which is not post-quantum secure". Sometimes the very first run after opening Firefox gives the X25519 (failing) result. "Often" varies. Sometimes it's around 10 fails out of 50 tests, other times it's 1 out of 50. It seems random.

I have read that sometimes networking equipment or even ISPs can be the cause of PQC requests falling back to non-PQC due to the long keys in PQC, but I do not see this intermittent issue with Chrome or Edge on the same computer/network/ISP as Firefox. I have not seen a single failure so far on those two browsers. The only variable I am aware of is the web browser.

I also tried connecting to a cellular hotspot as well as disabling my Norton 360 firewall and the results are the same as above.

Looking for help to resolve this issue. Thanks.

Hello, I have been testing all browsers I use (Firefox, Chrome, Edge) on [https://pq.cloudflareresearch.com/ Cloudflare Post-Quantum Key Agreement] to verify PQC support. They all support the X25519MLKEM768 hybrid scheme (i.e. Cloudflare web page returns "''You are using X25519MLKEM768 which is post-quantum secure''"). The issue: When I run the test in Firefox multiple times by doing repeated hard refreshes (Ctrl+Shift+R), quite often the result is "''You are using X25519 which is not post-quantum secure''". Sometimes the very first run after opening Firefox gives the X25519 (failing) result. "Often" varies. Sometimes it's around 10 fails out of 50 tests, other times it's 1 out of 50. It seems random. I have read that sometimes networking equipment or even ISPs can be the cause of PQC requests falling back to non-PQC due to the long keys in PQC, but I do not see this intermittent issue with Chrome or Edge on the same computer/network/ISP as Firefox. I have not seen a single failure so far on those two browsers. The only variable I am aware of is the web browser. I also tried connecting to a cellular hotspot as well as disabling my Norton 360 firewall and the results are the same as above. Looking for help to resolve this issue. Thanks.
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Hi, it would be better to file a bug on https://bugzilla.mozilla.org. Thanks!

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