Protocol specification

Common standards

Hashes

Most of the time SHA-512 hashes are used, however RIPEMD-160 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":

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-256)
79a324faeebcbf9849f310545ed531556882487e (with ripemd-160)

Common structures

All integers are encoded in big endian. (This is different from Bitcoin).

Message structure

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
4	checksum	uint32_t	First 4 bytes of sha512(payload)
?	payload	uchar[]	The actual data

Known magic values:

Magic value	Sent over wire as
0xE9BEB4D9	E9 BE B4 D9

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.

Value	Storage length	Format
< 0xfd	1	uint8_t
<= 0xffff	3	0xfd followed by the length as uint16_t
<= 0xffffffff	5	0xfe followed by the length as uint32_t
-	9	0xff followed by the length 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 variable length integers 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...

Network address

When a network address is needed somewhere, this structure is used. This protocol and structure supports IPv6, but note that the original client currently only supports IPv4 networking. Network addresses are not prefixed with a timestamp in the version message.

Field Size	Description	Data type	Comments
4	time	uint32	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. The original client only supports IPv4 and only reads the last 4 bytes to get the IPv4 address. However, the IPv4 address is written into the message as a 16 byte IPv4-mapped IPv6 address (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

Unencrypted Message Data

Field Size	Description	Data type	Comments
1+	msg_version	var_int	Message format version
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 )
20	destination ripe	uchar[]	The ripe hash of the public key of the receiver of the message
1+	encoding	var_int	Message Encoding 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 everything from the msg_version to the ack_data.

Message Encodings

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

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.

Pubkey bitfield features

Bit	Name	Description
0	undefined	The most significant bit at the beginning of the structure. Undefined
1	undefined	The next most significant bit. Undefined
...	...	...
30	undefined	The second-least significant bit. Undefined
31	does_ack	If true, the receiving node does send acknowledgements (rather than dropping them).

Message types

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.

Payload:

Field Size	Description	Data type	Comments
4	version	int32_t	Identifies protocol version being used by the node
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
26	addr_from	net_addr	The network address of the node emitting this message
8	nonce	uint64_t	Random nonce used to detect connections to self.
1+	user_agent	var_str	User Agent (0x00 if string is 0 bytes long)
1+	stream numbers	var_int_list	The stream numbers that the emitting node is interested in.

A "verack" packet shall be sent if the version packet was accepted.

The following services are currently assigned:

Value	Name	Description
1	NODE_NETWORK	This is a normal network node.

verack

The verack message is sent in reply to version. This message consists of only a message header with the command string "verack".

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)
34x?	addr_list	net_addr	Address of other nodes on the network.

inv

Allows a node to advertise its knowledge of one or more objects. It can be received unsolicited, or in reply to getmessages.

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

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.

Field Size	Description	Data type	Comments
8	POW nonce	uint64_t	Random nonce used for the Proof Of Work
4	time	uint32_t	The time that this message was generated and broadcast
1+	address version	var_int	The address' version
1+	stream number	var_int	The address' stream number
20	pub key hash	uchar[]	The ripemd hash of the public key

pubkey

A public key

Field Size	Description	Data type	Comments
8	POW nonce	uint64_t	Random nonce used for the Proof Of Work
4	time	uint32_t	The time that this message was generated and broadcast.
1+	address version	var_int	The address' version
1+	stream number	var_int	The address' stream number
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 )

msg

Used for person-to-person messages.

Field Size	Description	Data type	Comments
8	POW nonce	uint64_t	Random nonce used for the Proof Of Work
4	time	uint32_t	The time that this message was generated and broadcast
1+	streamNumber	var_int	The stream number of the destination address.
?	encrypted	uchar[]	Encrypted data. (Todo: Add details describing the encryption format) See also Unencrypted Message Data Format

broadcast

Broadcast messages are sent in-the-clear. Users who are subscribed to the sending address will see the message appear in their inbox.

Field Size	Description	Data type	Comments
8	POW nonce	uint64_t	The Proof Of Work nonce
4	time	uint32_t	The time that the message was broadcast
1+	broadcast version	var_int	The version number of this broadcast protocol message.
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 )
20	address hash	uchar[]	The sender's address hash. This is included so that nodes can more cheaply detect whether this is a broadcast message for which they are listening, although it must be verified with the public key above.
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 covers everything from the broadcast version down through the message. This will soon be changed to cover everything from the time down through the message.