fix: update handling of ja4 alpn edge cases #4755
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lrstewart
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Sep 5, 2024
stuffer/s2n_stuffer.h
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166
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| */ | ||
| S2N_RESULT s2n_hex_digit(uint8_t nibble, uint8_t *hex_digit); |
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Adding "stuffer" to the name to match the module makes this confusing, because it doesn't actually take a stuffer. But I'm not sure where else this function should live :/
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Agree with not adding the prefix. Perhaps renaming it to something like nibble_to_hex might clarify its purpose?
jouho
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Sep 6, 2024
stuffer/s2n_stuffer.h
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166
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167
| */ | ||
| S2N_RESULT s2n_hex_digit(uint8_t nibble, uint8_t *hex_digit); |
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Agree with not adding the prefix. Perhaps renaming it to something like nibble_to_hex might clarify its purpose?
jouho
approved these changes
Sep 6, 2024
goatgoose
reviewed
Sep 9, 2024
goatgoose
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Sep 9, 2024
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Resolved issues:
Related to FoxIO-LLC/ja4#148
Description of changes:
Update s2n-tls's handling of alpn edge cases to reflect the updates to the spec:
Two of the changes (handling of 1-byte alpns and handling of only one of the first or last characters not being alphanumeric) aren't official yet, but I'm implementing the current consensus answer / matching what wireshark does.
Call-outs:
I'll need to update the compliance comments once the spec is finalized. But this change doesn't technically lower our duvet coverage even in the meantime, because the spec didn't cover any of these cases :)
Testing:
Unit tests, and I was able to uncomment the JA4 pcap that didn't work before.
I also added our own pcap with a wide range of questionable alpn values. I had to add exceptions for a few of those alpn values, because wireshark will need to be updated to not allow values like "__". The cases that pcap covers:
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.