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

Kazuho Oku <notifications@github.com> Thu, 15 November 2018 08:40 UTC

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

My understanding is that we cannot change which bits are protected based on the use (or non-use) is spin bits, because the use is not negotiated.

Having the bit always outside the header protection also gives the non-participating endpoints greater freedom to play with the bits (e.g. always set to zero).

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