[quicwg/base-drafts] 5.6 Packet Number Protection is hard to follow (#1387)

[Tatsuhiro Tsujikawa <[e-mail]>]

It is hard to understand TLS 5.6 Packet Number Protection.

More specifically, this text block:

"""
   In sampling the packet ciphertext, the packet number length is
   assumed to be the smaller of the maximum possible packet number
   encoding (4 octets), or the size of the protected packet minus the
   minimum expansion for the AEAD.  For example, the sampled ciphertext
   for a packet with a short header can be determined by:

   "sample_offset = min(1 + connection_id_length + 4, packet_length -
   aead_expansion) sample =
   packet[sample_offset..sample_offset+sample_length] "
"""

It is ambiguous that what packet_length is.  Is it the Packet length field in Long packet header?  But it does not appear in Short header.  Is it the length of (Protected) Payload?  Or the length of QUIC packet?

The text says "the packet number length is ...", but the example seems to be offset to the byte to sample.

It would be also nice to show the example of Long packet.



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