Martin Milata
2 years ago
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# Reproducible build
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We want to invite the wider community to participate in the verification of
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the firmware built by SatoshiLabs. With reasonable effort you should be able to
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build the firmware and verify that it's identical to the official firmware.
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Trezor Firmware uses [Nix](https://nixos.org/), [Poetry](https://python-poetry.org/)
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and [Cargo](https://doc.rust-lang.org/cargo/) to make the build environment
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deterministic. We also provide a Docker-based script so that the build can be
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performed with a single command on usual x86 Linux system.
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## Building
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First you need to determine which *version tag* you want to build:
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* for Trezor One it is `legacy/vX.Y.Z`, e.g. `legacy/v1.10.3`,
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* for Trezor Model T it is `core/vX.Y.Z`, e.g. `core/v2.4.2`.
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Assuming you want to build `core/v2.4.2`:
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1. install [Docker](https://www.docker.com/)
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2. clone the firmware repository: `git clone https://github.com/trezor/trezor-firmware.git`
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3. go into the firmware directory: `cd trezor-firmware`
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4. checkout the version tag: `git checkout core/v2.4.2`
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5. run: `bash build-docker.sh core/v2.4.2`
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After the build finishes the firmware images are located in:
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* `build/legacy/firmware/firmware.bin` and `build/legacy-bitcoinonly/firmware/firmware.bin` for Trezor One,
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* `build/core/firmware/firmware.bin` and `build/core-bitcoinonly/firmware/firmware.bin` for Trezor Model T.
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## Verifying
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The result won't be bit-by-bit identical with the official images because the
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official images are signed while local builds aren't. Official release of
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Trezor One firmware also has additional 256-byte legacy header that needs to be
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removed first.
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### Trezor T
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The [firmware header](../hardware/model-t/boot.md#firmware-header) contains 65
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bytes of signature data at offset 0x15bf. After overwriting it by zeros in
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official release the binaries should become identical.
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```
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wget https://data.trezor.io/firmware/2/trezor-2.4.2.bin
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# the following line removes 65 bytes of signature data from the official firmware
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dd if=/dev/zero of=trezor-2.4.2.bin bs=1 seek=5567 count=65 conv=notrunc
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# the following two lines print out the hashes of the firmwares
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sha256sum trezor-2.4.2.bin
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sha256sum build/core/firmware/firmware.bin
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```
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### Trezor One
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Official T1 firmware starts with [256-byte legacy header](../hardware/model-one/firmware-format.md)
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used for compatibility with old bootloaders. Locally built firmware doesn't have this header.
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```
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wget https://data.trezor.io/firmware/1/trezor-1.10.3.bin
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# strip legacy header
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tail -c +257 trezor-1.10.3.bin > trezor-1.10.3-nolegacyhdr.bin
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```
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The [v2 header](../hardware/model-one/firmware-format.md#v2-header) has 3x65
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bytes of signature data at offset 0x220. Overwrite by zeros to obtain image
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identical to the one built locally.
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```
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dd if=/dev/zero of=trezor-1.10.3-nolegacyhdr.bin bs=1 seek=544 count=195 conv=notrunc
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sha256sum trezor-1.10.3-nolegacyhdr.bin
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sha256sum build/legacy/firmware/firmware.bin
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```
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_Note: Fingerprints displayed for T1 at the end of `build-docker.sh` do not match fingerprints of
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official firmware due to the legacy header._
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_Note: T1 firmware built this way won't boot because unsigned firmware needs to be built with
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[`MEMORY_PROTECT=0`](../legacy/index.md#combining-bootloader-and-firmware-with-various-memory_protect-settings-signedunsigned)._
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@ -0,0 +1,79 @@
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# Trezor One firmware format
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Historically Trezor One has been using 256-byte header (w/ `TRZR` magic string) followed by the
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actual firmware. Since version 1.8.0, different 1024-byte header (w/ `TRZF` magic string) is in use,
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and building firmware from this repository produces firmware image containing such header followed
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by firmware code.
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Official release firmware contains both these headers for compatibility with old bootloaders. That
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means there is a 256-byte `TRZR` header followed by 1024-byte `TRZF` header followed by code.
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* Hash function used for computing data digest for signatures is SHA256.
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* Signature system is ECDSA over SECP256k1.
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* All multibyte integer values are little endian.
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## Legacy Header
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Total length of legacy header is always 256 bytes.
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| offset | length | name | description |
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|-------:|-------:|------|-------------|
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| 0x0000 | 4 | magic | firmware magic `TRZR` |
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| 0x0004 | 4 | codelen | length of V2 header + code (length of code before 1.8.0) |
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| 0x0008 | 1 | sigindex1 | index of key for `sig1` |
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| 0x0009 | 1 | sigindex2 | index of key for `sig2` |
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| 0x000A | 1 | sigindex3 | index of key for `sig3` |
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| 0x000B | 1 | flags | unused since 1.8.0 (zeroed) |
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| 0x000C | 52 | reserved | not used yet (zeroed) |
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| 0x0040 | 64 | sig1 | signature #1 |
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| 0x0080 | 64 | sig2 | signature #2 |
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| 0x00C0 | 64 | sig3 | signature #3 |
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Signature verification:
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* Calculate SHA256 digest of firmware without this header.
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* Verify signature `sig1` of the digest against public key with index `sigindex1` in [`V1_BOOTLOADER_KEYS`](../../../python/src/trezorlib/firmware.py).
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* Repeat for `sig2` and `sig3`. Indexes must be distinct.
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## V2 Header
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This header has the same format as [Model T Firmware Header](../model-t/boot.md#firmware-header),
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however due to different signature scheme the `sigmask` and `sig` fields are zeroed and part of the
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reserved space is used for T1-specific fields `sig1`-`sig3`, `sigindex1-sigindex3`. Total length of
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v2 header is always 1024 bytes.
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| offset | length | name | description |
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|-------:|-------:|------|-------------|
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| 0x0000 | 4 | magic | firmware magic `TRZF` |
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| 0x0004 | 4 | hdrlen | length of the firmware header |
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| 0x0008 | 4 | expiry | valid until timestamp (0=infinity) |
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| 0x000C | 4 | codelen | length of the firmware code (without the header) |
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| 0x0010 | 1 | vmajor | version (major) |
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| 0x0011 | 1 | vminor | version (minor) |
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| 0x0012 | 1 | vpatch | version (patch) |
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| 0x0013 | 1 | vbuild | version (build) |
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| 0x0014 | 1 | fix_vmajor | version of last critical bugfix (major) |
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| 0x0015 | 1 | fix_vminor | version of last critical bugfix (minor) |
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| 0x0016 | 1 | fix_vpatch | version of last critical bugfix (patch) |
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| 0x0017 | 1 | fix_vbuild | version of last critical bugfix (build) |
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| 0x0018 | 8 | reserved | not used yet (zeroed) |
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| 0x0020 | 32 | hash1 | hash of the first code chunk excluding both the legacy and the v2 header (129792 B) |
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| 0x0040 | 32 | hash2 | hash of the second code chunk (128 KiB), zeroed if unused |
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| ... | ... | ... | ... |
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| 0x0200 | 32 | hash16 | hash of the last possible code chunk (128 KiB), zeroed if unused |
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| 0x0220 | 64 | sig1 | signature #1 |
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| 0x0260 | 64 | sig2 | signature #2 |
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| 0x02A0 | 64 | sig3 | signature #3 |
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| 0x02E0 | 1 | sigindex1 | index of key for `sig1` |
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| 0x02E1 | 1 | sigindex2 | index of key for `sig2` |
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| 0x02E2 | 1 | sigindex3 | index of key for `sig3` |
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| 0x02E3 | 220 | reserved | not used yet (zeroed) |
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| 0x03BF | 1 | reserved_sigmask | unused in T1 (zeroed) |
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| 0x03C0 | 64 | reserved_sig | unused in T1 (zeroed) |
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Signature verification:
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* Calculate SHA256 digest of the entire header with `sig1`-`sig3` and `sigindex1`-`sigindex3` zeroed
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out.
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* Verify signature `sig1` of the digest against public key with index `sigindex1` in [`V1_BOOTLOADER_KEYS`](../../../python/src/trezorlib/firmware.py).
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* Repeat for `sig2` and `sig3`. Indexes must be distinct.
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