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Adding Protocol specification to docs (WIP) #1727

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g1itch wants to merge 12 commits from doc into v0.6
pull from: doc
merge into: Bitmessage:v0.6
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docs/conf.py
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@ -19,7 +19,7 @@ import version # noqa:E402
# -- Project information -----------------------------------------------------
project = u'PyBitmessage'
copyright = u'2019, The Bitmessage Team' # pylint: disable=redefined-builtin
copyright = u'2019-2021, The Bitmessage Team' # pylint: disable=redefined-builtin
author = u'The Bitmessage Team'
# The short X.Y version

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+------------+-------------+-----------+--------------------------------------------+
| Field Size | Description | Data type | Comments |
+============+=============+===========+============================================+
| 16 | IV | uchar[] | Initialization Vector used for AES-256-CBC |
+------------+-------------+-----------+--------------------------------------------+
| 2 | Curve type | uint16_t | Elliptic Curve type 0x02CA (714) |
+------------+-------------+-----------+--------------------------------------------+
| 2 | X length | uint16_t | Length of X component of public key R |
+------------+-------------+-----------+--------------------------------------------+
| X length | X | uchar[] | X component of public key R |
+------------+-------------+-----------+--------------------------------------------+
| 2 | Y length | uint16_t | Length of Y component of public key R |
+------------+-------------+-----------+--------------------------------------------+
| Y length | Y | uchar[] | Y component of public key R |
+------------+-------------+-----------+--------------------------------------------+
| ? | encrypted | uchar[] | Cipher text |
+------------+-------------+-----------+--------------------------------------------+
| 32 | MAC | uchar[] | HMACSHA256 Message Authentication Code |
+------------+-------------+-----------+--------------------------------------------+

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Encryption
==========
Bitmessage uses the Elliptic Curve Integrated Encryption Scheme
`(ECIES) <http://en.wikipedia.org/wiki/Integrated_Encryption_Scheme>`_
to encrypt the payload of the Message and Broadcast objects.
The scheme uses Elliptic Curve Diffie-Hellman
`(ECDH) <http://en.wikipedia.org/wiki/ECDH>`_ to generate a shared secret used
to generate the encryption parameters for Advanced Encryption Standard with
256bit key and Cipher-Block Chaining
`(AES-256-CBC) <http://en.wikipedia.org/wiki/Advanced_Encryption_Standard>`_.
The encrypted data will be padded to a 16 byte boundary in accordance to
`PKCS7 <http://en.wikipedia.org/wiki/Cryptographic_Message_Syntax>`_. This
means that the data is padded with N bytes of value N.
The Key Derivation Function
`(KDF) <http://en.wikipedia.org/wiki/Key_derivation_function>`_ used to
generate the key material for AES is
`SHA512 <http://en.wikipedia.org/wiki/Sha512>`_. The Message Authentication
Code (MAC) scheme used is `HMACSHA256 <http://en.wikipedia.org/wiki/Hmac>`_.
Format
------
(See also: :doc:`protocol`)
.. include:: encrypted_payload.rst
In order to reconstitute a usable (65 byte) public key (starting with 0x04),
the X and Y components need to be expanded by prepending them with 0x00 bytes
until the individual component lengths are 32 bytes.
Encryption
----------
1. The destination public key is called K.
2. Generate 16 random bytes using a secure random number generator.
Call them IV.
3. Generate a new random EC key pair with private key called r and public key
called R.
4. Do an EC point multiply with public key K and private key r. This gives you
public key P.
5. Use the X component of public key P and calculate the SHA512 hash H.
6. The first 32 bytes of H are called key_e and the last 32 bytes are called
key_m.
7. Pad the input text to a multiple of 16 bytes, in accordance to PKCS7.
8. Encrypt the data with AES-256-CBC, using IV as initialization vector,
key_e as encryption key and the padded input text as payload. Call the
output cipher text.
9. Calculate a 32 byte MAC with HMACSHA256, using key_m as salt and
IV + R + cipher text as data. Call the output MAC.
The resulting data is: IV + R + cipher text + MAC
Decryption
----------
1. The private key used to decrypt is called k.
2. Do an EC point multiply with private key k and public key R. This gives you
public key P.
3. Use the X component of public key P and calculate the SHA512 hash H.
4. The first 32 bytes of H are called key_e and the last 32 bytes are called
key_m.
5. Calculate MAC' with HMACSHA256, using key_m as salt and
IV + R + cipher text as data.
6. Compare MAC with MAC'. If not equal, decryption will fail.
7. Decrypt the cipher text with AES-256-CBC, using IV as initialization
vector, key_e as decryption key and the cipher text as payload. The output
is the padded input text.
.. highlight:: nasm
Partial Example
---------------
.. list-table:: Public key K:
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
04 09 d4 e5 c0 ab 3d 25
fe 04 8c 64 c9 da 1a 24
2c 7f 19 41 7e 95 17 cd
26 69 50 d7 2c 75 57 13
58 5c 61 78 e9 7f e0 92
fc 89 7c 9a 1f 17 20 d5
77 0a e8 ea ad 2f a8 fc
bd 08 e9 32 4a 5d de 18
57
- Public key, 0x04 prefix, then 32 bytes X and 32 bytes Y.
.. list-table:: Initialization Vector IV:
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
bd db 7c 28 29 b0 80 38
75 30 84 a2 f3 99 16 81
- 16 bytes generated with a secure random number generator.
.. list-table:: Randomly generated key pair with private key r and public key R:
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
5b e6 fa cd 94 1b 76 e9
d3 ea d0 30 29 fb db 6b
6e 08 09 29 3f 7f b1 97
d0 c5 1f 84 e9 6b 8b a4
- Private key r
* -
::
04 02 93 21 3d cf 13 88
b6 1c 2a e5 cf 80 fe e6
ff ff c0 49 a2 f9 fe 73
65 fe 38 67 81 3c a8 12
92 df 94 68 6c 6a fb 56
5a c6 14 9b 15 3d 61 b3
b2 87 ee 2c 7f 99 7c 14
23 87 96 c1 2b 43 a3 86
5a
- Public key R
.. list-table:: Derived public key P (point multiply r with K):
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
04 0d b8 e3 ad 8c 0c d7
3f a2 b3 46 71 b7 b2 47
72 9b 10 11 41 57 9d 19
9e 0d c0 bd 02 4e ae fd
89 ca c8 f5 28 dc 90 b6
68 11 ab ac 51 7d 74 97
be 52 92 93 12 29 be 0b
74 3e 05 03 f4 43 c3 d2
96
- Public key P
* -
::
0d b8 e3 ad 8c 0c d7 3f
a2 b3 46 71 b7 b2 47 72
9b 10 11 41 57 9d 19 9e
0d c0 bd 02 4e ae fd 89
- X component of public key P
.. list-table:: SHA512 of public key P X component (H):
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
17 05 43 82 82 67 86 71
05 26 3d 48 28 ef ff 82
d9 d5 9c bf 08 74 3b 69
6b cc 5d 69 fa 18 97 b4
- First 32 bytes of H called key_e
* -
::
f8 3f 1e 9c c5 d6 b8 44
8d 39 dc 6a 9d 5f 5b 7f
46 0e 4a 78 e9 28 6e e8
d9 1c e1 66 0a 53 ea cd
- Last 32 bytes of H called key_m
.. list-table:: Padded input:
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
54 68 65 20 71 75 69 63
6b 20 62 72 6f 77 6e 20
66 6f 78 20 6a 75 6d 70
73 20 6f 76 65 72 20 74
68 65 20 6c 61 7a 79 20
64 6f 67 2e 04 04 04 04
- The quick brown fox jumps over the lazy dog.0x04,0x04,0x04,0x04
.. list-table:: Cipher text:
:header-rows: 1
:widths: auto
* - Data
- Comments
* -
::
64 20 3d 5b 24 68 8e 25
47 bb a3 45 fa 13 9a 5a
1d 96 22 20 d4 d4 8a 0c
f3 b1 57 2c 0d 95 b6 16
43 a6 f9 a0 d7 5a f7 ea
cc 1b d9 57 14 7b f7 23
- 3 blocks of 16 bytes of encrypted data.

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Extended encoding
=================
Extended encoding is an attempt to create a standard for transmitting structured
data. The goals are flexibility, wide platform support and extensibility. It is
currently available in the v0.6 branch and can be enabled by holding "Shift"
while clicking on Send. It is planned that v5 addresses will have to support
this. It's a work in progress, the basic plain text message works but don't
expect anthing else at this time.
The data structure is in msgpack, then compressed with zlib. The top level is
a key/value store, and the "" key (empty string) contains the value of the type
of object, which can then have its individual format and standards.
Text fields are encoded using UTF-8.
Types
-----
You can find the implementations in the ``src/messagetypes`` directory of
PyBitmessage. Each type has its own file which includes one class, and they are
dynamically loaded on startup. It's planned that this will also contain
initialisation, rendering and so on, so that developers can simply add a new
object type by adding a single file in the messagetypes directory and not have
to change any other part of the code.
message
^^^^^^^
The replacement for the old messages. Mandatory keys are ``body`` and
``subject``, others are currently not implemented and not mandatory. Proposed
other keys:
``parents``:
array of msgids referring to messages that logically precede it in a
conversation. Allows to create a threaded conversation view
``files``:
array of files (which is a key/value pair):
``name``:
file name, mandatory
``data``:
the binary data of the file
``type``:
MIME content type
``disposition``:
MIME content disposition, possible values are "inline" and "attachment"
vote
^^^^
Dummy code available in the repository. Supposed to serve voting in a chan
(thumbs up/down) for decentralised moderation. Does not actually do anything at
the moment and specification can change.

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@ -1,7 +1,17 @@
.. mdinclude:: ../README.md
:end-line: 20
Documentation
-------------
Protocol documentation
----------------------
.. toctree::
:maxdepth: 2
protocol
encryption
pow
Code documentation
------------------
.. toctree::
:maxdepth: 3
@ -14,3 +24,6 @@ Indices and tables
* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`
.. mdinclude:: ../README.md
:start-line: 21

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Proof of work
=============
This page describes Bitmessage's Proof of work ("POW") mechanism as it exists in
Protocol Version 3. In this document, hash() means SHA512(). SHA512 was chosen
as it is widely supported and so that Bitcoin POW hardware cannot trivially be
used for Bitmessage POWs. The author acknowledges that they are essentially the
same algorithm with a different key size.
Both ``averageProofOfWorkNonceTrialsPerByte`` and ``payloadLengthExtraBytes``
are set by the owner of a Bitmessage address. The default and minimum for each
is 1000. (This is the same as difficulty 1. If the difficulty is 2, then this
value is 2000). The purpose of ``payloadLengthExtraBytes`` is to add some extra
weight to small messages.
Do a POW
--------
Let us use a ``msg`` message as an example::
payload = embeddedTime + encodedObjectVersion + encodedStreamNumber + encrypted
``payloadLength``
the length of payload, in bytes, + 8
(to account for the nonce which we will append later)
``TTL``
the number of seconds in between now and the object expiresTime.
.. include:: pow_formula.rst
::
initialHash = hash(payload)
start with ``trialValue = 99999999999999999999``
also start with ``nonce = 0`` where nonce is 8 bytes in length and can be
hashed as if it is a string.
::
while trialValue > target:
nonce = nonce + 1
resultHash = hash(hash( nonce || initialHash ))
trialValue = the first 8 bytes of resultHash, converted to an integer
When this loop finishes, you will have your 8 byte nonce value which you can
prepend onto the front of the payload. The message is then ready to send.
Check a POW
-----------
Let us assume that ``payload`` contains the payload for a msg message (the nonce
down through the encrypted message data).
``nonce``
the first 8 bytes of payload
``dataToCheck``
the ninth byte of payload on down (thus it is everything except the nonce)
::
initialHash = hash(dataToCheck)
resultHash = hash(hash( nonce || initialHash ))
``POWValue``
the first eight bytes of resultHash converted to an integer
``TTL``
the number of seconds in between now and the object ``expiresTime``.
.. include:: pow_formula.rst
If ``POWValue`` is less than or equal to ``target``, then the POW check passes.

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.. math::
target = \frac{2^{64}}{{\displaystyle
nonceTrialsPerByte (payloadLength + payloadLengthExtraBytes + \frac{
TTL (payloadLength + payloadLengthExtraBytes)}{2^{16}})
}}

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Protocol specification
======================
.. warning:: All objects sent on the network should support protocol v3
starting on Sun, 16 Nov 2014 22:00:00 GMT.
.. toctree::
:maxdepth: 2
Common standards
----------------
Hashes
^^^^^^
Most of the time `SHA-512 <http://en.wikipedia.org/wiki/SHA-2>`_ hashes are
used, however `RIPEMD-160 <http://en.wikipedia.org/wiki/RIPEMD>`_ is also used
when creating an address.
A double-round of SHA-512 is used for the Proof Of Work. Example of
double-SHA-512 encoding of string "hello":
.. highlight:: nasm
::
hello
9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2dff72519673ca72323c3d99ba5c11d7c7acc6e14b8c5da0c4663475c2e5c3adef46f73bcdec043(first round of sha-512)
0592a10584ffabf96539f3d780d776828c67da1ab5b169e9e8aed838aaecc9ed36d49ff1423c55f019e050c66c6324f53588be88894fef4dcffdb74b98e2b200(second round of sha-512)
For Bitmessage addresses (RIPEMD-160) this would give:
::
hello
9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2dff72519673ca72323c3d99ba5c11d7c7acc6e14b8c5da0c4663475c2e5c3adef46f73bcdec043(first round is sha-512)
79a324faeebcbf9849f310545ed531556882487e (with ripemd-160)
Common structures
-----------------
All integers are encoded in big endian. (This is different from Bitcoin).
.. list-table:: Message structure
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 4
- magic
- uint32_t
- Magic value indicating message origin network, and used to seek to next
message when stream state is unknown
* - 12
- command
- char[12]
- ASCII string identifying the packet content, NULL padded (non-NULL
padding results in packet rejected)
* - 4
- length
- uint32_t
- Length of payload in number of bytes. Because of other restrictions,
there is no reason why this length would ever be larger than 1600003
bytes. Some clients include a sanity-check to avoid processing messages
which are larger than this.
* - 4
- checksum
- uint32_t
- First 4 bytes of sha512(payload)
* - ?
- message_payload
- uchar[]
- The actual data, a :ref:`message <msg-types>` or an object_.
Not to be confused with objectPayload.
Known magic values:
+-------------+-------------------+
| Magic value | Sent over wire as |
+=============+===================+
| 0xE9BEB4D9 | E9 BE B4 D9 |
+-------------+-------------------+
.. _varint:
Variable length integer
^^^^^^^^^^^^^^^^^^^^^^^
Integer can be encoded depending on the represented value to save space.
Variable length integers always precede an array/vector of a type of data that
may vary in length. Varints MUST use the minimum possible number of bytes to
encode a value. For example, the value 6 can be encoded with one byte therefore
a varint that uses three bytes to encode the value 6 is malformed and the
decoding task must be aborted.
+---------------+----------------+------------------------------------------+
| Value | Storage length | Format |
+===============+================+==========================================+
| < 0xfd | 1 | uint8_t |
+---------------+----------------+------------------------------------------+
| <= 0xffff | 3 | 0xfd followed by the integer as uint16_t |
+---------------+----------------+------------------------------------------+
| <= 0xffffffff | 5 | 0xfe followed by the integer as uint32_t |
+---------------+----------------+------------------------------------------+
| - | 9 | 0xff followed by the integer as uint64_t |
+---------------+----------------+------------------------------------------+
Variable length string
^^^^^^^^^^^^^^^^^^^^^^
Variable length string can be stored using a variable length integer followed by
the string itself.
+------------+-------------+------------+----------------------------------+
| Field Size | Description | Data type | Comments |
+============+=============+============+==================================+
| 1+ | length | |var_int| | Length of the string |
+------------+-------------+------------+----------------------------------+
| ? | string | char[] | The string itself (can be empty) |
+------------+-------------+------------+----------------------------------+
Variable length list of integers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
n integers can be stored using n+1 :ref:`variable length integers <varint>`
where the first var_int equals n.
+------------+-------------+-----------+----------------------------+
| Field Size | Description | Data type | Comments |
+============+=============+===========+============================+
| 1+ | count | |var_int| | Number of var_ints below |
+------------+-------------+-----------+----------------------------+
| 1+ | | var_int | The first value stored |
+------------+-------------+-----------+----------------------------+
| 1+ | | var_int | The second value stored... |
+------------+-------------+-----------+----------------------------+
| 1+ | | var_int | etc... |
+------------+-------------+-----------+----------------------------+
.. |var_int| replace:: :ref:`var_int <varint>`
Network address
^^^^^^^^^^^^^^^
When a network address is needed somewhere, this structure is used. Network
addresses are not prefixed with a timestamp or stream in the version_ message.
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 8
- time
- uint64
- the Time.
* - 4
- stream
- uint32
- Stream number for this node
* - 8
- services
- uint64_t
- same service(s) listed in version_
* - 16
- IPv6/4
- char[16]
- IPv6 address. IPv4 addresses are written into the message as a 16 byte
`IPv4-mapped IPv6 address <http://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresses>`_
(12 bytes 00 00 00 00 00 00 00 00 00 00 FF FF, followed by the 4 bytes of
the IPv4 address).
* - 2
- port
- uint16_t
- port number
Inventory Vectors
^^^^^^^^^^^^^^^^^
Inventory vectors are used for notifying other nodes about objects they have or
data which is being requested. Two rounds of SHA-512 are used, resulting in a
64 byte hash. Only the first 32 bytes are used; the later 32 bytes are ignored.
Inventory vectors consist of the following data format:
+------------+-------------+-----------+--------------------+
| Field Size | Description | Data type | Comments |
+============+=============+===========+====================+
| 32 | hash | char[32] | Hash of the object |
+------------+-------------+-----------+--------------------+
Encrypted payload
^^^^^^^^^^^^^^^^^
Bitmessage uses `ECIES <https://en.wikipedia.org/wiki/Integrated_Encryption_Scheme>`_ to encrypt its messages. For more information see :doc:`encryption`
.. include:: encrypted_payload.rst
Unencrypted Message Data
^^^^^^^^^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 1+
- msg_version
- var_int
- Message format version. **This field is not included after the
protocol v3 upgrade period**.
* - 1+
- address_version
- var_int
- Sender's address version number. This is needed in order to calculate
the sender's address to show in the UI, and also to allow for forwards
compatible changes to the public-key data included below.
* - 1+
- stream
- var_int
- Sender's stream number
* - 4
- behavior bitfield
- uint32_t
- A bitfield of optional behaviors and features that can be expected from
the node with this pubkey included in this msg message (the sender's
pubkey).
* - 64
- public signing key
- uchar[]
- The ECC public key used for signing (uncompressed format;
normally prepended with \x04)
* - 64
- public encryption key
- uchar[]
- The ECC public key used for encryption (uncompressed format;
normally prepended with \x04)
* - 1+
- nonce_trials_per_byte
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is the
average number of nonce trials a node will have to perform to meet the
Proof of Work requirement. 1000 is the network minimum so any lower
values will be automatically raised to 1000. **This field is new and is
only included when the address_version >= 3**.
* - 1+
- extra_bytes
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is added
to the data length to make sending small messages more difficult.
1000 is the network minimum so any lower values will be automatically
raised to 1000. **This field is new and is only included when the
address_version >= 3**.
* - 20
- destination ripe
- uchar[]
- The ripe hash of the public key of the receiver of the message
* - 1+
- encoding
- var_int
- :ref:`Message Encoding <msg-encodings>` type
* - 1+
- message_length
- var_int
- Message Length
* - message_length
- message
- uchar[]
- The message.
* - 1+
- ack_length
- var_int
- Length of the acknowledgement data
* - ack_length
- ack_data
- uchar[]
- The acknowledgement data to be transmitted. This takes the form of a
Bitmessage protocol message, like another msg message. The POW therein
must already be completed.
* - 1+
- sig_length
- var_int
- Length of the signature
* - sig_length
- signature
- uchar[]
- The ECDSA signature which covers the object header starting with the
time, appended with the data described in this table down to the
ack_data.
.. _msg-encodings:
Message Encodings
"""""""""""""""""
.. list-table::
:header-rows: 1
:widths: auto
* - Value
- Name
- Description
* - 0
- IGNORE
- Any data with this number may be ignored. The sending node might simply
be sharing its public key with you.
* - 1
- TRIVIAL
- UTF-8. No 'Subject' or 'Body' sections. Useful for simple strings
of data, like URIs or magnet links.
* - 2
- SIMPLE
- UTF-8. Uses 'Subject' and 'Body' sections. No MIME is used.
::
messageToTransmit = 'Subject:' + subject + '\n' + 'Body:' + message
* - 3
- EXTENDED
- See :doc:`extended_encoding`
Further values for the message encodings can be decided upon by the community.
Any MIME or MIME-like encoding format, should they be used, should make use of
Bitmessage's 8-bit bytes.
.. _behavior-bitfield:
Pubkey bitfield features
""""""""""""""""""""""""
.. list-table::
:header-rows: 1
:widths: auto
* - Bit
- Name
- Description
* - 0
- undefined
- The most significant bit at the beginning of the structure. Undefined
* - 1
- undefined
- The next most significant bit. Undefined
* - ...
- ...
- ...
* - 27
- onion_router
- (**Proposal**) Node can be used to onion-route messages. In theory any
node can onion route, but since it requires more resources, they may have
the functionality disabled. This field will be used to indicate that the
node is willing to do this.
* - 28
- forward_secrecy
- (**Proposal**) Receiving node supports a forward secrecy encryption
extension. The exact design is pending.
* - 29
- chat
- (**Proposal**) Address if for chatting rather than messaging.
* - 30
- include_destination
- (**Proposal**) Receiving node expects that the RIPE hash encoded in their
address preceedes the encrypted message data of msg messages bound for
them.
.. note:: since hardly anyone implements this, this will be redesigned as
`simple recipient verification <https://github.com/Bitmessage/PyBitmessage/pull/808#issuecomment-170189856>`_
* - 31
- does_ack
- If true, the receiving node does send acknowledgements (rather than
dropping them).
.. _msg-types:
Message types
-------------
Undefined messages received on the wire must be ignored.
version
^^^^^^^
When a node creates an outgoing connection, it will immediately advertise its
version. The remote node will respond with its version. No futher communication
is possible until both peers have exchanged their version.
.. list-table:: Payload
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 4
- version
- int32_t
- Identifies protocol version being used by the node. Should equal 3.
Nodes should disconnect if the remote node's version is lower but
continue with the connection if it is higher.
* - 8
- services
- uint64_t
- bitfield of features to be enabled for this connection
* - 8
- timestamp
- int64_t
- standard UNIX timestamp in seconds
* - 26
- addr_recv
- net_addr
- The network address of the node receiving this message (not including the
time or stream number)
* - 26
- addr_from
- net_addr
- The network address of the node emitting this message (not including the
time or stream number and the ip itself is ignored by the receiver)
* - 8
- nonce
- uint64_t
- Random nonce used to detect connections to self.
* - 1+
- user_agent
- var_str
- :doc:`useragent` (0x00 if string is 0 bytes long). Sending nodes must not
include a user_agent longer than 5000 bytes.
* - 1+
- stream_numbers
- var_int_list
- The stream numbers that the emitting node is interested in. Sending nodes
must not include more than 160000 stream numbers.
A "verack" packet shall be sent if the version packet was accepted. Once you
have sent and received a verack messages with the remote node, send an addr
message advertising up to 1000 peers of which you are aware, and one or more
inv messages advertising all of the valid objects of which you are aware.
.. list-table:: The following services are currently assigned
:header-rows: 1
:widths: auto
* - Value
- Name
- Description
* - 1
- NODE_NETWORK
- This is a normal network node.
* - 2
- NODE_SSL
- This node supports SSL/TLS in the current connect (python < 2.7.9 only
supports a SSL client, so in that case it would only have this on when
the connection is a client).
* - 3
- NODE_POW
- (**Proposal**) This node may do PoW on behalf of some its peers (PoW
offloading/delegating), but it doesn't have to. Clients may have to meet
additional requirements (e.g. TLS authentication)
* - 4
- NODE_DANDELION
- Node supports `dandelion <https://github.com/gfanti/bips/blob/master/bip-dandelion.mediawiki>`_
verack
^^^^^^
The *verack* message is sent in reply to *version*. This message consists of
only a :ref:`message header <Message structure>` with the command string
"verack". The TCP timeout starts out at 20 seconds; after verack messages are
exchanged, the timeout is raised to 10 minutes.
If both sides announce that they support SSL, they MUST perform a SSL handshake
immediately after they both send and receive verack. During this SSL handshake,
the TCP client acts as a SSL client, and the TCP server acts as a SSL server.
The current implementation (v0.5.4 or later) requires the AECDH-AES256-SHA
cipher over TLSv1 protocol, and prefers the secp256k1 curve (but other curves
may be accepted, depending on the version of python and OpenSSL used).
addr
^^^^
Provide information on known nodes of the network. Non-advertised nodes should
be forgotten after typically 3 hours
Payload:
+------------+-------------+-----------+---------------------------------------+
| Field Size | Description | Data type | Comments |
+============+=============+===========+=======================================+
| 1+ | count | |var_int| | Number of address entries (max: 1000) |
+------------+-------------+-----------+---------------------------------------+
| 38 | addr_list | net_addr | Address of other nodes on the network.|
+------------+-------------+-----------+---------------------------------------+
inv
^^^
Allows a node to advertise its knowledge of one or more objects. Payload
(maximum payload length: 50000 items):
+------------+-------------+------------+-----------------------------+
| Field Size | Description | Data type | Comments |
+============+=============+============+=============================+
| ? | count | |var_int| | Number of inventory entries |
+------------+-------------+------------+-----------------------------+
| 32x? | inventory | inv_vect[] | Inventory vectors |
+------------+-------------+------------+-----------------------------+
getdata
^^^^^^^
getdata is used in response to an inv message to retrieve the content of a
specific object after filtering known elements.
Payload (maximum payload length: 50000 entries):
+------------+-------------+------------+-----------------------------+
| Field Size | Description | Data type | Comments |
+============+=============+============+=============================+
| ? | count | |var_int| | Number of inventory entries |
+------------+-------------+------------+-----------------------------+
| 32x? | inventory | inv_vect[] | Inventory vectors |
+------------+-------------+------------+-----------------------------+
object
^^^^^^
An object is a message which is shared throughout a stream. It is the only
message which propagates; all others are only between two nodes. Objects have a
type, like 'msg', or 'broadcast'. To be a valid object, the
:doc:`pow` must be done. The maximum allowable length of an object
(not to be confused with the ``objectPayload``) is |2^18| bytes.
.. |2^18| replace:: 2\ :sup:`18`\
.. list-table:: Message structure
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 8
- nonce
- uint64_t
- Random nonce used for the :doc:`pow`
* - 8
- expiresTime
- uint64_t
- The "end of life" time of this object (be aware, in version 2 of the
protocol this was the generation time). Objects shall be shared with
peers until its end-of-life time has been reached. The node should store
the inventory vector of that object for some extra period of time to
avoid reloading it from another node with a small time delay. The time
may be no further than 28 days + 3 hours in the future.
* - 4
- objectType
- uint32_t
- Four values are currently defined: 0-"getpubkey", 1-"pubkey", 2-"msg",
3-"broadcast". All other values are reserved. Nodes should relay objects
even if they use an undefined object type.
* - 1+
- version
- var_int
- The object's version. Note that msg objects won't contain a version
until Sun, 16 Nov 2014 22:00:00 GMT.
* - 1+
- stream number
- var_int
- The stream number in which this object may propagate
* - ?
- objectPayload
- uchar[]
- This field varies depending on the object type; see below.
Object types
------------
Here are the payloads for various object types.
getpubkey
^^^^^^^^^
When a node has the hash of a public key (from an address) but not the public
key itself, it must send out a request for the public key.
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 20
- ripe
- uchar[]
- The ripemd hash of the public key. This field is only included when the
address version is <= 3.
* - 32
- tag
- uchar[]
- The tag derived from the address version, stream number, and ripe. This
field is only included when the address version is >= 4.
pubkey
^^^^^^
A version 2 pubkey. This is still in use and supported by current clients but
*new* v2 addresses are not generated by clients.
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 4
- |behavior_bitfield|
- uint32_t
- A bitfield of optional behaviors and features that can be expected from
the node receiving the message.
* - 64
- public signing key
- uchar[]
- The ECC public key used for signing (uncompressed format;
normally prepended with \x04 )
* - 64
- public encryption key
- uchar[]
- The ECC public key used for encryption (uncompressed format;
normally prepended with \x04 )
.. list-table:: A version 3 pubkey
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 4
- |behavior_bitfield|
- uint32_t
- A bitfield of optional behaviors and features that can be expected from
the node receiving the message.
* - 64
- public signing key
- uchar[]
- The ECC public key used for signing (uncompressed format;
normally prepended with \x04 )
* - 64
- public encryption key
- uchar[]
- The ECC public key used for encryption (uncompressed format;
normally prepended with \x04 )
* - 1+
- nonce_trials_per_byte
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is the
average number of nonce trials a node will have to perform to meet the
Proof of Work requirement. 1000 is the network minimum so any lower
values will be automatically raised to 1000.
* - 1+
- extra_bytes
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is added
to the data length to make sending small messages more difficult.
1000 is the network minimum so any lower values will be automatically
raised to 1000.
* - 1+
- sig_length
- var_int
- Length of the signature
* - sig_length
- signature
- uchar[]
- The ECDSA signature which, as of protocol v3, covers the object
header starting with the time, appended with the data described in this
table down to the extra_bytes.
.. list-table:: A version 4 pubkey
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 32
- tag
- uchar[]
- The tag, made up of bytes 32-64 of the double hash of the address data
(see example python code below)
* - ?
- encrypted
- uchar[]
- Encrypted pubkey data.
When version 4 pubkeys are created, most of the data in the pubkey is encrypted.
This is done in such a way that only someone who has the Bitmessage address
which corresponds to a pubkey can decrypt and use that pubkey. This prevents
people from gathering pubkeys sent around the network and using the data from
them to create messages to be used in spam or in flooding attacks.
In order to encrypt the pubkey data, a double SHA-512 hash is calculated from
the address version number, stream number, and ripe hash of the Bitmessage
address that the pubkey corresponds to. The first 32 bytes of this hash are used
to create a public and private key pair with which to encrypt and decrypt the
pubkey data, using the same algorithm as message encryption
(see :doc:`encryption`). The remaining 32 bytes of this hash are added to the
unencrypted part of the pubkey and used as a tag, as above. This allows nodes to
determine which pubkey to decrypt when they wish to send a message.
In PyBitmessage, the double hash of the address data is calculated using the
python code below:
.. code-block:: python
doubleHashOfAddressData = hashlib.sha512(hashlib.sha512(
encodeVarint(addressVersionNumber) + encodeVarint(streamNumber) + hash
).digest()).digest()
.. list-table:: Encrypted data in version 4 pubkeys:
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 4
- |behavior_bitfield|
- uint32_t
- A bitfield of optional behaviors and features that can be expected from
the node receiving the message.
* - 64
- public signing key
- uchar[]
- The ECC public key used for signing (uncompressed format;
normally prepended with \x04 )
* - 64
- public encryption key
- uchar[]
- The ECC public key used for encryption (uncompressed format;
normally prepended with \x04 )
* - 1+
- nonce_trials_per_byte
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is the
average number of nonce trials a node will have to perform to meet the
Proof of Work requirement. 1000 is the network minimum so any lower
values will be automatically raised to 1000.
* - 1+
- extra_bytes
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is added
to the data length to make sending small messages more difficult.
1000 is the network minimum so any lower values will be automatically
raised to 1000.
* - 1+
- sig_length
- var_int
- Length of the signature
* - sig_length
- signature
- uchar[]
- The ECDSA signature which covers everything from the object header
starting with the time, then appended with the decrypted data down to
the extra_bytes. This was changed in protocol v3.
msg
^^^
Used for person-to-person messages. Note that msg objects won't contain a
version in the object header until Sun, 16 Nov 2014 22:00:00 GMT.
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - ?
- encrypted
- uchar[]
- Encrypted data. See `Encrypted payload`_.
See also `Unencrypted Message Data`_
broadcast
^^^^^^^^^
Users who are subscribed to the sending address will see the message appear in
their inbox. Broadcasts are version 4 or 5.
Pubkey objects and v5 broadcast objects are encrypted the same way: The data
encoded in the sender's Bitmessage address is hashed twice. The first 32 bytes
of the resulting hash constitutes the "private" encryption key and the last
32 bytes constitute a **tag** so that anyone listening can easily decide if
this particular message is interesting. The sender calculates the public key
from the private key and then encrypts the object with this public key. Thus
anyone who knows the Bitmessage address of the sender of a broadcast or pubkey
object can decrypt it.
The version of broadcast objects was previously 2 or 3 but was changed to 4 or
5 for protocol v3. Having a broadcast version of 5 indicates that a tag is used
which, in turn, is used when the sender's address version is >=4.
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 32
- tag
- uchar[]
- The tag. This field is new and only included when the broadcast version
is >= 5. Changed in protocol v3
* - ?
- encrypted
- uchar[]
- Encrypted broadcast data. The keys are derived as described in the
paragraph above. See Encrypted payload for details about the encryption
algorithm itself.
Unencrypted data format:
.. list-table::
:header-rows: 1
:widths: auto
* - Field Size
- Description
- Data type
- Comments
* - 1+
- broadcast version
- var_int
- The version number of this broadcast protocol message which is equal
to 2 or 3. This is included here so that it can be signed. This is
no longer included in protocol v3
* - 1+
- address version
- var_int
- The sender's address version
* - 1+
- stream number
- var_int
- The sender's stream number
* - 4
- |behavior_bitfield|
- uint32_t
- A bitfield of optional behaviors and features that can be expected from
the owner of this pubkey.
* - 64
- public signing key
- uchar[]
- The ECC public key used for signing (uncompressed format;
normally prepended with \x04)
* - 64
- public encryption key
- uchar[]
- The ECC public key used for encryption (uncompressed format;
normally prepended with \x04)
* - 1+
- nonce_trials_per_byte
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is the
average number of nonce trials a node will have to perform to meet the
Proof of Work requirement. 1000 is the network minimum so any lower
values will be automatically raised to 1000. This field is new and is
only included when the address_version >= 3.
* - 1+
- extra_bytes
- var_int
- Used to calculate the difficulty target of messages accepted by this
node. The higher this value, the more difficult the Proof of Work must
be before this individual will accept the message. This number is added
to the data length to make sending small messages more difficult.
1000 is the network minimum so any lower values will be automatically
raised to 1000. This field is new and is only included when the
address_version >= 3.
* - 1+
- encoding
- var_int
- The encoding type of the message
* - 1+
- messageLength
- var_int
- The message length in bytes
* - messageLength
- message
- uchar[]
- The message
* - 1+
- sig_length
- var_int
- Length of the signature
* - sig_length
- signature
- uchar[]
- The signature which did cover the unencrypted data from the broadcast
version down through the message. In protocol v3, it covers the
unencrypted object header starting with the time, all appended with
the decrypted data.
.. |behavior_bitfield| replace:: :ref:`behavior bitfield <behavior-bitfield>`

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User Agent
==========
Bitmessage user agents are a modified browser user agent with more structure
to aid parsers and provide some coherence. The user agent strings are arranged
in a stack with the most underlying software listed first.
Basic format::
/Name:Version/Name:Version/.../
Example::
/PyBitmessage:0.2.2/Corporate Mail System:0.8/
/Surdo:5.64/surdo-qt:0.4/
The version numbers are not defined to any strict format, although this guide
recommends:
* Version numbers in the form of Major.Minor.Revision (2.6.41)
* Repository builds using a date in the format of YYYYMMDD (20110128)
For git repository builds, implementations are free to use the git commitish.
However the issue lies in that it is not immediately obvious without the
repository which version preceeds another. For this reason, we lightly
recommend dates in the format specified above, although this is by no means
a requirement.
Optional ``-r1``, ``-r2``, ... can be appended to user agent version numbers.
This is another light recommendation, but not a requirement. Implementations
are free to specify version numbers in whatever format needed insofar as it
does not include ``(``, ``)``, ``:`` or ``/`` to interfere with the user agent
syntax.
An optional comments field after the version number is also allowed. Comments
should be delimited by parenthesis ``(...)``. The contents of comments is
entirely implementation defined although this document recommends the use of
semi-colons ``;`` as a delimiter between pieces of information.
Example::
/cBitmessage:0.2(iPad; U; CPU OS 3_2_1)/AndroidBuild:0.8/
Reserved symbols are therefore: ``/ : ( )``
They should not be misused beyond what is specified in this section.
``/``
separates the code-stack
``:``
specifies the implementation version of the particular stack
``( and )``
delimits a comment which optionally separates data using ``;``