166 lines
6.9 KiB
Markdown
166 lines
6.9 KiB
Markdown
# Levin Protocol
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This is a document explaining the current design of the levin protocol, as
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used by Monero. The protocol is largely inherited from cryptonote, but has
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undergone some changes.
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This document also may differ from the `struct bucket_head2` in Monero's
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code slightly - the spec here is slightly more strict to allow for
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extensibility.
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One of the goals of this document is to clearly indicate what is being sent
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"on the wire" to identify metadata that could de-anonymize users over I2P/Tor.
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These issues will be addressed as they are found. See `ANONMITY_NETWORKS.md` in
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the `docs` folder for any outstanding issues.
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> This document does not currently list all data being sent by the monero
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> protocol, that portion is a work-in-progress. Please take the time to do it
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> if interested in learning about Monero p2p traffic!
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## Header
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This header is sent for every Monero p2p message.
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```
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0 1 2 3
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 0x01 | 0x21 | 0x01 | 0x01 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 0x01 | 0x01 | 0x01 | 0x01 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Length |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| E. Response | Command
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Return Code
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|Q|S|B|E| Reserved
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 0x01 | 0x00 | 0x00 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 0x00 |
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+-+-+-+-+-+-+-+-+
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```
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### Signature
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The first 8 bytes are the "signature" which helps identify the protocol (in
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case someone connected to the wrong port, etc). The comments indicate that byte
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sequence is from "benders nightmare".
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This also can be used by deep packet inspection (DPI) engines to identify
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Monero when the link is not encrypted. SSL has been proposed as a means to
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mitigate this issue, but BIP-151 or the Noise protocol should also be considered.
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### Length
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The length is an unsigned 64-bit little endian integer. The length does _not_
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include the header.
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The implementation currently rejects received messages that exceed 100 MB
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(base 10) by default.
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### Expect Response
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A zero-byte if no response is expected from the peer, and a non-zero byte if a
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response is expected from the peer. Peers must respond to requests with this
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flag in the same order that they were received, however, other messages can be
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sent between responses.
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There are some commands in the
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[cryptonote protocol](#cryptonote-protocol-commands) where a response is
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expected from the peer, but this flag is not set. Those responses are returned
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as notify messages and can be sent in any order by the peer.
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### Command
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An unsigned 32-bit little endian integer representing the Monero specific
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command being invoked.
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### Return Code
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A signed 32-bit little integer integer representing the response from the peer
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from the last command that was invoked. This is `0` for request messages.
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### Flags
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* `Q` - Bit is set if the message is a request.
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* `S` - Bit is set if the message is a response.
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* `B` - Bit is set if this is a the beginning of a [fragmented message](#fragmented-messages).
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* `E` - Bit is set if this is the end of a [fragmented message](#fragmented-messages).
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### Version
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A fixed value of `1` as an unsigned 32-bit little endian integer.
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## Message Flow
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The protocol can be subdivided into: (1) notifications, (2) requests,
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(3) responses, (4) fragmented messages, and (5) dummy messages. Response
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messages must be sent in the same order that a peer issued a request message.
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A peer does not have to send a response immediately following a request - any
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other message type can be sent instead.
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### Notifications
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Notifications are one-way messages that can be sent at any time without
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an expectation of a response from the peer. The `Q` bit must be set, the `S`,
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`B` and `E` bits must be unset, and the `Expect Response` field must be zeroed.
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Some notifications must be in response to other notifications. This is not
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part of the levin messaging layer, and is described in the
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[commands](#commands) section.
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### Requests
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Requests are the basis of the admin protocol for Monero. The `Q` bit must be
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set, the `S`, `B` and `E` bits must be unset, and the `Expect Response` field
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must be non-zero. The peer is expected to send a response message with the same
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`command` number.
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### Responses
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Response message can only be sent after a peer first issues a request message.
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Responses must have the `S` bit set, the `Q`, `B` and `E` bits unset, and have
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a zeroed `Expect Response` field. The `Command` field must be the same value
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that was sent in the request message. The `Return Code` is specific to the
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`Command` being issued (see [commands])(#commands)).
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### Fragmented
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Fragmented messages were introduced for the "white noise" feature for i2p/tor.
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A transaction can be sent in fragments to conceal when "real" data is being
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sent instead of dummy messages. Only one fragmented message can be sent at a
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time, and bits `B` and `E` are never set at the same time
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(see [dummy messages](#dummy)). The re-constructed message must contain a
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levin header for a different (non-fragment) message type.
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The `Q` and `S` bits are never set and the `Expect Response` field must always
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be zero. The first fragment has the `B` bit set, neither `B` nor `E` is set for
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"middle" fragments, and `E` is set for the last fragment.
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### Dummy
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Dummy messages have the `B` and `E` bits set, the `Q` and `S` bits unset, and
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the `Expect Reponse` field zeroed. When a message of this type is received, the
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contents can be safely ignored.
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## Commands
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### P2P (Admin) Commands
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#### (`1001` Request) Handshake
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#### (`1001` Response) Handshake
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#### (`1002` Request) Timed Sync
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#### (`1002` Response) Timed Sync
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#### (`1003` Request) Ping
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#### (`1003` Response) Ping
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#### (`1004` Request) Stat Info
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#### (`1004` Response) Stat Info
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#### (`1005` Request) Network State
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#### (`1005` Response) Network State
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#### (`1006` Request) Peer ID
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#### (`1006` Reponse) Peer ID
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#### (`1007` Request) Support Flags
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#### (`1007` Response) Support Flags
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### Cryptonote Protocol Commands
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#### (`2001` Notification) New Block
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#### (`2002` Notification) New Transactions
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#### (`2003` Notification) Request Get Objects
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#### (`2004` Notification) Response Get Objects
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#### (`2006` Notification) Request Chain
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#### (`2007` Notification) Response Chain Entry
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#### (`2008` Notification) New Fluffy Block
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#### (`2009` Notification) Request Fluffy Missing TX
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