Subject: [Drip] More on HHIT - HIT Suite ID

From: Robert Moskowitz <[email-masked]>
Date: Wed, 14 Oct 2020 21:17:09 -0400

In RFC 7401 sec 5.2.10:

    The ID field in the HIT_SUITE_LIST is defined as an eight-bit field,
    as opposed to the four-bit HIT Suite ID and OGA ID field in the
    ORCHID.  This difference is a measure to accommodate larger HIT Suite
    IDs if the 16 available values prove insufficient.  In that case, one
    of the 16 values, zero, will be used to indicate that four additional
    bits of the ORCHID will be used to encode the HIT Suite ID. Hence,
    the current four-bit HIT Suite IDs only use the four higher-order
    bits in the ID field.  Future documents may define the use of the
    four lower-order bits in the ID field.

    The following HIT Suite IDs are defined, and the relationship between
    the four-bit ID value used in the OGA ID field and the eight-bit
    encoding within the HIT_SUITE_LIST ID field is clarified:

         HIT Suite       Four-bit ID    Eight-bit encoding

         RESERVED            0             0x00
         RSA,DSA/SHA-256     1             0x10           (REQUIRED)
         ECDSA/SHA-384       2             0x20 (RECOMMENDED)
         ECDSA_LOW/SHA-1     3             0x30 (RECOMMENDED)

    The following table provides more detail on the above HIT Suite
    combinations.  The input for each generation algorithm is the
    encoding of the HI as defined in Section 3.2.  The output is 96 bits
    long and is directly used in the ORCHID.

This was Rene's idea to allow for long-term growth of HIT suites. Note 
that OrchidV2 does not accommodate this.  It cannot handle an 8 bit OGA 
ID and return a 92 bit hash.  Perhaps an Errata, or as hinted above, for 
future work.

Like now????

Going with the HHIT field order of:

Prefix || RAA || HDA || SID || HiHash

If the SID is 0n, i.e. 8 bits.  n = {a-f} could be allocated for HDA 
local use.  Or some smaller set of values.

Is this something worth doing or opening a can of worms?