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84 lines
4.1 KiB
Markdown
84 lines
4.1 KiB
Markdown
# Trezor Protocol
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## version 1
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Messages are sent in packets of 64 bytes.
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First packet has the following structure:
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| offset | length | type | contents |
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|--------|--------|-------------|---------------------------------------------------------------------------------------|
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| 0 | 3 | char[3] | '?##' magic constant |
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| 3 | 2 | BE uint16_t | numerical [message type](messages.proto#L76) |
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| 5 | 4 | BE uint32_t | message size |
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| 9 | 55 | uint8_t[55] | first 55 bytes of message encoded in Protocol Buffers (padded with zeroes if shorter) |
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Following packets has the following structure:
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| offset | length | type | contents |
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|--------|--------|-------------|----------------------------------------------------------------------------------------|
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| 0 | 1 | char[1] | '?' magic constant |
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| 1 | 63 | uint8_t[63] | following bytes of message encoded in Protocol Buffers (padded with zeroes if shorter) |
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## Adding new message
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To add new message to Trezor protocol follow these steps:
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1. Reconsider if there isn't already a message, that would suit your needs.
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2. Choose the right place (file) to put new message:
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- [`messages.proto`](messages.proto) are for management of the messages itself (wire type to message type mapping and etc.)
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- [`messages-common.proto`](messages-common.proto) are for common messages
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- all other files have a suffix `messages-SUFFIX.proto`, where suffix describes specific use case of messages contained within the file
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3. Add new message and comment it properly following our [Messages naming and documenting conventions](#messages-naming-and-documenting-conventions).
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4. If message is not embedded in another message, it has to have a wire type number assigned. This number is used to map
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between Trezor wire identifier (uint) and a protobuf message. Mapping is defined in [`messages.proto`](messages.proto#L76). You have to find the lowest
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free number and assign it to new message.
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## Messages naming and documenting conventions
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Message names must:
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- be as self explanatory as possible
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- have `Ack` suffix if the message is a received message (send from host to device) and serves as a response to some request made by device before
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(e.g. initial messages from host to device doesn't have to have this suffix)
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Documenting/commenting the messages is mandatory. Please use the following template:
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```protobuf
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/**
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* MSG_TYPE: Description of the message
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* MSG_FLOW_TAG
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* MSG_FLOW_TAG
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* ...
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*/
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```
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where:
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- `MSG_TYPE` is used to describe the purpose of the message and its type. Possible values are:
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- `Request` for inbound messages (coming to the device (Trezor))
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- `Response` for outbound messages (coming out from the device)
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- in case that the message is embedded in another message we don't state the message type
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- `MSG_FLOW_TAG` denotes the flow of the messages in a session (use case). Possible tags are:
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- `@start` means that this message is first
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- `@end` means that this message is last
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- `@next` denotes messages that could follow after this message
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- `@embed` denotes messages that are embedded into other message(s)
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- `@auxstart` - denotes message for sub-flow start; this message might appear at any time
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during any other flow. When the corresponding @auxend message is processed, the original
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flow resumes.
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- `@auxend` - see `@auxstart`
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Messages flow is checked at the compile time.
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Using the template and the rules we can create for example this messages:
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```protobuf
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/**
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* Request: Ask device to sign transaction
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* @start
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* @next TxRequest
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* @next Failure
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*/
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```
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```protobuf
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/**
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* Structure representing BIP32 (hierarchical deterministic) node
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* Used for imports of private key into the device and exporting public key out of device
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* @embed
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*/
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```
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