Doc updates to include additional ALPN extension values#277
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…LPN Extension Value
…g in the ALPN Extension Value
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While you do clarify with the exact hex values, it might be worth putting the word "ASCII" in there somewhere when saying alphanumeric (since RFC 7301 clearly anticipates UTF-8 strings (which are not used.) |
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Thanks @johnthacker, I had a go at tweaking based on your feedback. |
vlvkobal
approved these changes
Jan 26, 2026
This was referenced May 9, 2026
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Overview
Adding examples to cover space character (
sp,0x20) handling in the ALPN Extension Value as we have seen some unexpected JA4 fingerprints in Wireshark when a space character is sent by the client.ℹ️ Please note, I have also raised an issue over on the Wireshark repo to highlight what we have seen: https://gitlab.com/wireshark/wireshark/-/issues/20966
Example 1
ALPN Extension Value sent by client:
ALPN Next Protocol: ' ' Hex values: 0x20Resulting JA4 Fingerprint (Note: double space in place of ALPN value)
Expected JA4 Fingerprint
Example 2
ALPN Extension Value sent by client:
ALPN Next Protocol: 'a ' Hex values: 0x61 0x20Resulting JA4 Fingerprint (Note: sinlge space set for second ALPN value)
Expected JA4 Fingerprint