trezor-firmware/docs/hardware/model-one/firmware-format.md

Trezor One firmware format

Historically Trezor One has been using 256-byte header (w/ TRZR magic string) followed by the actual firmware. Since version 1.8.0, different 1024-byte header (w/ TRZF magic string) is in use, and building firmware from this repository produces firmware image containing such header followed by firmware code.

Official release firmware contains both these headers for compatibility with old bootloaders. That means there is a 256-byte TRZR header followed by 1024-byte TRZF header followed by code.

• Hash function used for computing data digest for signatures is SHA256.
• Signature system is ECDSA over SECP256k1.
• All multibyte integer values are little endian.

Legacy Header

Total length of legacy header is always 256 bytes.

offset	length	name	description
0x0000	4	magic	firmware magic TRZR
0x0004	4	codelen	length of V2 header + code (length of code before 1.8.0)
0x0008	1	sigindex1	index of key for sig1
0x0009	1	sigindex2	index of key for sig2
0x000A	1	sigindex3	index of key for sig3
0x000B	1	flags	unused since 1.8.0 (zeroed)
0x000C	52	reserved	not used yet (zeroed)
0x0040	64	sig1	signature #1
0x0080	64	sig2	signature #2
0x00C0	64	sig3	signature #3

Signature verification:

• Calculate SHA256 digest of firmware without this header.
• Verify signature sig1 of the digest against public key with index sigindex1 in V1_BOOTLOADER_KEYS.
• Repeat for sig2 and sig3. Indexes must be distinct.

V2 Header

This header has the same format as Model T Firmware Header, however due to different signature scheme the sigmask and sig fields are zeroed and part of the reserved space is used for T1-specific fields sig1-sig3, sigindex1-sigindex3. Total length of v2 header is always 1024 bytes.

offset	length	name	description
0x0000	4	magic	firmware magic TRZF
0x0004	4	hdrlen	length of the firmware header
0x0008	4	expiry	valid until timestamp (0=infinity)
0x000C	4	codelen	length of the firmware code (without the header)
0x0010	1	vmajor	version (major)
0x0011	1	vminor	version (minor)
0x0012	1	vpatch	version (patch)
0x0013	1	vbuild	version (build)
0x0014	1	fix_vmajor	version of last critical bugfix (major)
0x0015	1	fix_vminor	version of last critical bugfix (minor)
0x0016	1	fix_vpatch	version of last critical bugfix (patch)
0x0017	1	fix_vbuild	version of last critical bugfix (build)
0x0018	8	reserved	not used yet (zeroed)
0x0020	32	hash1	hash of the first code chunk excluding both the legacy and the v2 header (129792 B)
0x0040	32	hash2	hash of the second code chunk (128 KiB), zeroed if unused
...	...	...	...
0x0200	32	hash16	hash of the last possible code chunk (128 KiB), zeroed if unused
0x0220	64	sig1	signature #1
0x0260	64	sig2	signature #2
0x02A0	64	sig3	signature #3
0x02E0	1	sigindex1	index of key for sig1
0x02E1	1	sigindex2	index of key for sig2
0x02E2	1	sigindex3	index of key for sig3
0x02E3	220	reserved	not used yet (zeroed)
0x03BF	1	reserved_sigmask	unused in T1 (zeroed)
0x03C0	64	reserved_sig	unused in T1 (zeroed)

Signature verification:

• Calculate SHA256 digest of the entire header with sig1-sig3 and sigindex1-sigindex3 zeroed out.
• Verify signature sig1 of the digest against public key with index sigindex1 in V1_BOOTLOADER_KEYS.
• Repeat for sig2 and sig3. Indexes must be distinct.