Re: [quicwg/base-drafts] Example of ChaCha20-Poly1305 (#3712)

Martin Thomson <notifications@github.com> Tue, 02 June 2020 10:11 UTC

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Date: Tue, 02 Jun 2020 03:11:43 -0700
From: Martin Thomson <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Example of ChaCha20-Poly1305 (#3712)
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@martinthomson commented on this pull request.



> +      73573685608597d0efcb076b0ab7a7a4
+
+ku  = HKDF-Expand-Label(secret, "quic ku", _, 32)
+    = 1223504755036d556342ee9361d25342
+      1a826c9ecdf3c7148684b36b714881f9
+~~~
+
+The following shows the steps involved in protecting a minimal packet with an
+empty Destination Connection ID. This packet contains a single PING frame (that
+is, a payload of just 0x01) and has a packet number of 654360564. In this
+example, using a packet number of length 3 (that is, 49140 is encoded) avoids
+having to pad the payload of the packet; PADDING frames would be needed if the
+packet number is encoded on fewer octets.
+
+~~~
+pn                 = 654360564 (decimal)

It's hard to believe that this number came out of a random number generator, but that's where it came from.  That `pn & 0xffffff == pn & 0ffff` is also pure chance, but it seems like a useful property to try to use.

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