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.
|
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 time down through the message. |