Re: [quicwg/base-drafts] First octet changes (#2006)

[ianswett <[e-mail]>]

ianswett commented on this pull request.



> +with the remaining bytes.
+
+{{pseudo-hp}} shows a sample algorithm for applying header protection. Removing
+protection only differs in the order in which the packet number length
+(pn_length) is determined.
+
+~~~
+mask = header_protection(hp_key, sample)
+
+pn_length = (packet[0] & 0x03) + 1
+if packet[0] & 0x80 == 0x80:
+   # Long header: 4 bits masked
+   packet[0] ^= mask[0] & 0x0f
+else:
+   # Short header: 5 bits masked
+   packet[0] ^= mask[0] & 0x1f

One reason to choose a fixed value per connection is it makes it easier to detect which connections are not spinning.  Another reason is it's easy to leak information in that bit, so it's safer to just set a fixed value.

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