trezor-firmware/common/protob/protocol.md

Trezor Protocol

version 1

Messages are sent in packets of 64 bytes.

First packet has the following structure:

offset	length	type	contents
0	3	char[3]	'?##' magic constant
3	2	BE uint16_t	numerical message type
5	4	BE uint32_t	message size
9	55	uint8_t[55]	first 55 bytes of message encoded in Protocol Buffers (padded with zeroes if shorter)

Following packets has the following structure:

offset	length	type	contents
0	1	char[1]	'?' magic constant
1	63	uint8_t[63]	following bytes of message encoded in Protocol Buffers (padded with zeroes if shorter)