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TITH                                              THIS ISN'T THAT HARD
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Publication:  TTS‑0003
Revision:     1
Title:        Common TLV Types
Author(s):    Stephen Hurd
Date:         2025‑11‑15
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Status of this document
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  This document is a TITH Technical Standard (TTS) — it specifies
  the current technical requirements and recommendations for TITH
  software developers, coordinators and sysops of the Fidonet network
  and other networks using FTN technology.

  This document is released to the public domain, and may be used,
  copied or modified for any purpose whatever.

Abstract
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  Overall, TITH uses a tagged TLV structure.  This document describes
  how the types are assigned and used.

Contents
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  1.  Introduction
  2.  Reservation
  3.  Defined Types

  A. References
  B. History

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1. Introduction
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  In TITH, data is encoded as a hierarchy of TLV values with every
  value having a context‐specific meaning.  However, there's a few
  general encodings that will be reused across different contexts, so
  it's good to have a small number of well known types that won't be
  redfined based on the context.


2. Reservation
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  The first thirty‐two, numbered zero to thirty‐one are reserved for
  types specified in this document.  These types can not be redefined
  by any other TITH standard in any context.


3. Defined Types
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  These are the defined types and their data format at the time of
  this writing:

  0.  Invalid
      A type of zero will never be used.  If it is encountered, the
      implementation MUST stop processing the TLV data.

  1.  Origin
      This type contains the 5D address as specified by TTS‑0004.
      This address identifies the public key to use for signing
      operations at this level and below.

  2.  Signature
      The value is the 64 binary bytes of data output from the
      Libhydrogen hydro_sign_create() or hydro_sign_final_create()
      function.  The context parameter should be the C string
      "SignTLV" which is the code points U+53, U+69, U+67, U+6E, U+54,
      U+4C, U+56, U+00.  Implementations SHOULD ensure this is exactly
      64 bytes, and MUST pass the value, the public key of the
      appropriate Origin address, the specified context value, and the
      accompanying SignedData value to hydro_sign_verify().  If there
      is no applicable Origin or SignedData, the implementation SHOULD
      notify the appropriate entities of the error.  If the signature
      does not verify, the implementation MUST NOT parse any data from
      the SignedData field and SHOULD notify the appropriate entities
      (Sysop, Origin, etc) of the error.

  3.  SignedData
      The value is binary data that can be validated by a Signature
      that MUST accompany the data at the same level and the public
      key of the Origin at either the same level or above.  That is to
      say the most recently defined origin in the tree.  For example,
      given data with the following structure:

      OuterTLV
       ├──🭬Origin1
       ├──🭬GenericData1
       ├─┬🭬Group1
       │ ├──🭬Origin2
       │ ├──🭬SignedData1
       │ ╰──🭬Signature1
       ├─┬🭬Group2
       │ ├──🭬SignedData2
       │ ╰──🭬Signature2
       ╰─┬🭬Group3
         ╰─┬🭬Group4
           ╰─┬🭬Origin3
             ╰─┬🭬Group4
               ╰─┬🭬Origin4
                 ╰─┬🭬Group5
                   ├──🭬SignedData3
                   ╰──🭬Signature3

      SignedData1 will be signed using the public key of Origin2,
      SignedData2 will be signed using the public key of Origin1, and
      SignedData3 will be signed using the public key of Origin4.

  4.  SignedTLV
      The value begins with a sequence of TLV values in the order
      Origin, SignedData, Signature.  The Origin value is optional,
      and may be left out if an Origin has been established earlier.
      SignedData and Signature values are required.  The data in the
      SignedData value MUST be TLV encoded as described in TTS‑0002.
      The purpose of this type is to allow specifications to permit
      some or all TLV values to be replaced by a SignedTLV value.

  5.  Timestamp
      The value is encoded in the same manner as the Type and Length
      parts of a TLV value.  The number encoded is the POSIX Seconds
      Since the Epoch, defined in XBD4.19.  This is the value returned
      by time(NULL) on POSIX systems.  Despite popular belief, this is
      NOT the number of seconds since the beginning of January 1st,
      1970 but rather the number of complete days since January 1st,
      1970 times 86400, plus the number of seconds that have passed so
      far in the current day.  That is to say that the existence of
      leap seconds is pretended out of existence by this definition.

  6.  Destination
      This type contains the text representation of a 5D address as
      specified by TTS‑0004.


A. References
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  [TTS‑0002] "Type Length Value Encoding" TITH, 2025‑11‑14.

  [FTA‑1006] "Keywords to indicate requirement levels" FTSC,
  2000‑01‑17.

  [Libhydrogen] Version 1,
  https://github.com/jedisct1/libhydrogen/wiki

  [POSIX] "The Open Group Base Specifications Issue 8"
  https://pubs.opengroup.org/onlinepubs/9799919799/

  [XBD4.19] "Seconds Since the Epoch"
  https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap04.html#tag_04_19


B. History
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   Rev.1, 2025‑11‑15: Initial Release.

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