Subject: [Perc] Magnus Westerlund's Discuss on draft-ietf-perc-srtp-ekt-diet-11: (with DISCUSS)

From: Magnus Westerlund via Datatracker <[email-masked]>
Date: Wed, 05 Feb 2020 07:18:21 -0800

Magnus Westerlund has entered the following ballot position for
draft-ietf-perc-srtp-ekt-diet-11: Discuss

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DISCUSS:
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I think there are an important discrpency between the figure and the ABNF for
the full EKT message in section 4.1:

Figure 1:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     :                                                               :
     :                        EKT Ciphertext                         :
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Security Parameter Index    | Length                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 1 0|
     +-+-+-+-+-+-+-+-+

The ABNF parts that appears relevant:

    EKTCiphertext = 1*256BYTE ; EKTEncrypt(EKTKey, EKTPlaintext)
    Epoch = 2BYTE
    SPI = 2BYTE

    FullEKTField = EKTCiphertext SPI Epoch EKTMsgLength EKTMsgTypeFull

Note that the above ABNF states that the SPI is followed by a 16-bit Epoch
field prior to the length field.

Can you please ensure that this discrepancy is clarified.