Started formatting the Protocol Specification:
in index.rst README.md is splitted in two parts - References now in the bottom of the page; protocol.rst is the separate file, referenced on top. Closes: #1033
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.. mdinclude:: ../README.md
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:end-line: 20
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:doc:`protocol`
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Documentation
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-------------
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@ -21,3 +25,6 @@ Indices and tables
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* :ref:`genindex`
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* :ref:`modindex`
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* :ref:`search`
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.. mdinclude:: ../README.md
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:start-line: 21
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@ -0,0 +1,220 @@
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Protocol specification
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======================
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.. toctree::
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:maxdepth: 2
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Common standards
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----------------
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Hashes
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^^^^^^
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Most of the time `SHA-512 <http://en.wikipedia.org/wiki/SHA-2>`_ hashes are
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used, however `RIPEMD-160 <http://en.wikipedia.org/wiki/RIPEMD>`_ is also used
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when creating an address.
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A double-round of SHA-512 is used for the Proof Of Work. Example of
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double-SHA-512 encoding of string "hello":
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.. highlight:: nasm
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::
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hello
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9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2dff72519673ca72323c3d99ba5c11d7c7acc6e14b8c5da0c4663475c2e5c3adef46f73bcdec043(first round of sha-512)
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0592a10584ffabf96539f3d780d776828c67da1ab5b169e9e8aed838aaecc9ed36d49ff1423c55f019e050c66c6324f53588be88894fef4dcffdb74b98e2b200(second round of sha-512)
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For Bitmessage addresses (RIPEMD-160) this would give:
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::
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hello
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9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2dff72519673ca72323c3d99ba5c11d7c7acc6e14b8c5da0c4663475c2e5c3adef46f73bcdec043(first round is sha-512)
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79a324faeebcbf9849f310545ed531556882487e (with ripemd-160)
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Common structures
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-----------------
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All integers are encoded in big endian. (This is different from Bitcoin).
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.. list-table:: Message structure
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:header-rows: 1
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:widths: auto
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* - Field Size
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- Description
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- Data type
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- Comments
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* - 4
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- magic
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- uint32_t
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- Magic value indicating message origin network, and used to seek to next
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message when stream state is unknown
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* - 12
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- command
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- char[12]
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- ASCII string identifying the packet content, NULL padded (non-NULL
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padding results in packet rejected)
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* - 4
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- length
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- uint32_t
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- Length of payload in number of bytes. Because of other restrictions,
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there is no reason why this length would ever be larger than 1600003
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bytes. Some clients include a sanity-check to avoid processing messages
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which are larger than this.
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* - 4
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- checksum
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- uint32_t
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- First 4 bytes of sha512(payload)
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* - ?
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- message_payload
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- uchar[]
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- The actual data, a message or an object_. Not to be confused with
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objectPayload.
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Known magic values:
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+-------------+-------------------+
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| Magic value | Sent over wire as |
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+=============+===================+
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| 0xE9BEB4D9 | E9 BE B4 D9 |
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+-------------+-------------------+
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.. _varint:
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Variable length integer
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^^^^^^^^^^^^^^^^^^^^^^^
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Integer can be encoded depending on the represented value to save space.
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Variable length integers always precede an array/vector of a type of data that
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may vary in length. Varints MUST use the minimum possible number of bytes to
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encode a value. For example, the value 6 can be encoded with one byte therefore
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a varint that uses three bytes to encode the value 6 is malformed and the
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decoding task must be aborted.
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+---------------+----------------+------------------------------------------+
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| Value | Storage length | Format |
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+===============+================+==========================================+
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| < 0xfd | 1 | uint8_t |
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+---------------+----------------+------------------------------------------+
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| <= 0xffff | 3 | 0xfd followed by the integer as uint16_t |
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+---------------+----------------+------------------------------------------+
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| <= 0xffffffff | 5 | 0xfe followed by the integer as uint32_t |
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+---------------+----------------+------------------------------------------+
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| - | 9 | 0xff followed by the integer as uint64_t |
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+---------------+----------------+------------------------------------------+
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Variable length string
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^^^^^^^^^^^^^^^^^^^^^^
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Variable length string can be stored using a variable length integer followed by
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the string itself.
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+------------+-------------+------------+----------------------------------+
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| Field Size | Description | Data type | Comments |
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+============+=============+============+==================================+
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| 1+ | length | |var_int| | Length of the string |
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+------------+-------------+------------+----------------------------------+
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| ? | string | char[] | The string itself (can be empty) |
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+------------+-------------+------------+----------------------------------+
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Variable length list of integers
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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n integers can be stored using n+1 :ref:`variable length integers <varint>`
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where the first var_int equals n.
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+------------+-------------+-----------+----------------------------+
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| Field Size | Description | Data type | Comments |
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+============+=============+===========+============================+
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| 1+ | count | |var_int| | Number of var_ints below |
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+------------+-------------+-----------+----------------------------+
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| 1+ | | var_int | The first value stored |
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+------------+-------------+-----------+----------------------------+
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| 1+ | | var_int | The second value stored... |
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+------------+-------------+-----------+----------------------------+
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| 1+ | | var_int | etc... |
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+------------+-------------+-----------+----------------------------+
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.. |var_int| replace:: :ref:`var_int <varint>`
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Network address
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^^^^^^^^^^^^^^^
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When a network address is needed somewhere, this structure is used. Network
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addresses are not prefixed with a timestamp or stream in the version_ message.
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.. list-table::
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:header-rows: 1
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:widths: auto
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* - Field Size
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- Description
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- Data type
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- Comments
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* - 8
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- time
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- uint64
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- the Time.
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* - 4
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- stream
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- uint32
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- Stream number for this node
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* - 8
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- services
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- uint64_t
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- same service(s) listed in version
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* - 16
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- IPv6/4
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- char[16]
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- IPv6 address. IPv4 addresses are written into the message as a 16 byte
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`IPv4-mapped IPv6 address <http://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresses>`_
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(12 bytes 00 00 00 00 00 00 00 00 00 00 FF FF, followed by the 4 bytes of
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the IPv4 address).
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* - 2
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- port
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- uint16_t
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- port number
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Inventory Vectors
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^^^^^^^^^^^^^^^^^
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Inventory vectors are used for notifying other nodes about objects they have or
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data which is being requested. Two rounds of SHA-512 are used, resulting in a
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64 byte hash. Only the first 32 bytes are used; the later 32 bytes are ignored.
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Inventory vectors consist of the following data format:
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+------------+-------------+-----------+--------------------+
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| Field Size | Description | Data type | Comments |
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+============+=============+===========+====================+
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| 32 | hash | char[32] | Hash of the object |
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+------------+-------------+-----------+--------------------+
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Encrypted payload
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^^^^^^^^^^^^^^^^^
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Bitmessage uses `ECIES <https://en.wikipedia.org/wiki/Integrated_Encryption_Scheme>`_ to encrypt its messages. For more information see Encryption
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+------------+-------------+-----------+--------------------------------------------+
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| Field Size | Description | Data type | Comments |
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+============+=============+===========+============================================+
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| 16 | IV | uchar[] | Initialization Vector used for AES-256-CBC |
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+------------+-------------+-----------+--------------------------------------------+
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| 2 | Curve type | uint16_t | Elliptic Curve type 0x02CA (714) |
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+------------+-------------+-----------+--------------------------------------------+
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| 2 | X length | uint16_t | Length of X component of public key R |
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+------------+-------------+-----------+--------------------------------------------+
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| X length | X | uchar[] | X component of public key R |
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+------------+-------------+-----------+--------------------------------------------+
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| 2 | Y length | uint16_t | Length of Y component of public key R |
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+------------+-------------+-----------+--------------------------------------------+
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| Y length | Y | uchar[] | Y component of public key R |
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+------------+-------------+-----------+--------------------------------------------+
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| ? | encrypted | uchar[] | Cipher text |
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+------------+-------------+-----------+--------------------------------------------+
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| 32 | MAC | uchar[] | HMACSHA256 Message Authentication Code |
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+------------+-------------+-----------+--------------------------------------------+
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