diff --git a/core/tools/headertool.py b/core/tools/headertool.py
new file mode 100755
index 0000000000..11598ff7b0
--- /dev/null
+++ b/core/tools/headertool.py
@@ -0,0 +1,162 @@
+#!/usr/bin/env python3
+import click
+
+from trezorlib import cosi, firmware
+from trezorlib._internal import firmware_headers
+
+from typing import List, Tuple
+
+# =========================== signing =========================
+
+
+def sign_with_privkeys(digest: bytes, privkeys: List[bytes]) -> bytes:
+    """Locally produce a CoSi signature."""
+    pubkeys = [cosi.pubkey_from_privkey(sk) for sk in privkeys]
+    nonces = [cosi.get_nonce(sk, digest, i) for i, sk in enumerate(privkeys)]
+
+    global_pk = cosi.combine_keys(pubkeys)
+    global_R = cosi.combine_keys(R for r, R in nonces)
+
+    sigs = [
+        cosi.sign_with_privkey(digest, sk, global_pk, r, global_R)
+        for sk, (r, R) in zip(privkeys, nonces)
+    ]
+
+    signature = cosi.combine_sig(global_R, sigs)
+    try:
+        cosi.verify_combined(signature, digest, global_pk)
+    except Exception as e:
+        raise click.ClickException(f"Failed to produce valid signature.") from e
+
+    return signature
+
+
+def parse_privkey_args(privkey_data: List[str]) -> Tuple[int, List[bytes]]:
+    privkeys = []
+    sigmask = 0
+    for key in privkey_data:
+        try:
+            idx, key_hex = key.split(":", maxsplit=1)
+            privkeys.append(bytes.fromhex(key_hex))
+            sigmask |= 1 << (int(idx) - 1)
+        except ValueError:
+            click.echo(f"Could not parse key: {key}")
+            click.echo("Keys must be in the format: <key index>:<hex-encoded key>")
+            raise click.ClickException("Unrecognized key format.")
+    return sigmask, privkeys
+
+
+# ===================== CLI actions =========================
+
+
+def do_replace_vendorheader(fw, vh_file) -> None:
+    if not isinstance(fw, firmware_headers.FirmwareImage):
+        raise click.ClickException("Invalid image type (must be firmware).")
+
+    vh = firmware.VendorHeader.parse(vh_file.read())
+    if vh.header_len != fw.fw.vendor_header.header_len:
+        raise click.ClickException("New vendor header must have the same size.")
+
+    fw.fw.vendor_header = vh
+
+
+@click.command()
+@click.option("-n", "--dry-run", is_flag=True, help="Do not save changes.")
+@click.option("-h", "--rehash", is_flag=True, help="Force recalculate hashes.")
+@click.option("-v", "--verbose", is_flag=True, help="Show verbose info about headers.")
+@click.option(
+    "-S",
+    "--sign-private",
+    "privkey_data",
+    multiple=True,
+    help="Private key to use for signing.",
+)
+@click.option(
+    "-D", "--sign-dev-keys", is_flag=True, help="Sign with development header keys."
+)
+@click.option(
+    "-s", "--signature", "insert_signature", nargs=2, help="Insert external signature."
+)
+@click.option("-V", "--replace-vendor-header", type=click.File("rb"))
+@click.option(
+    "-d",
+    "--digest",
+    "print_digest",
+    is_flag=True,
+    help="Only output fingerprint for signing.",
+)
+@click.argument("firmware_file", type=click.File("rb+"))
+def cli(
+    firmware_file,
+    verbose,
+    rehash,
+    dry_run,
+    privkey_data,
+    sign_dev_keys,
+    insert_signature,
+    replace_vendor_header,
+    print_digest,
+):
+    firmware_data = firmware_file.read()
+
+    try:
+        fw = firmware_headers.parse_image(firmware_data)
+    except Exception as e:
+        import traceback
+
+        traceback.print_exc()
+        magic = firmware_data[:4]
+        raise click.ClickException(
+            f"Could not parse file (magic bytes: {magic!r})"
+        ) from e
+
+    digest = fw.digest()
+    if print_digest:
+        click.echo(digest.hex())
+        return
+
+    if replace_vendor_header:
+        do_replace_vendorheader(fw, replace_vendor_header)
+
+    if rehash:
+        fw.rehash()
+
+    if sign_dev_keys:
+        privkeys = fw.DEV_KEYS
+        sigmask = fw.DEV_KEY_SIGMASK
+    else:
+        sigmask, privkeys = parse_privkey_args(privkey_data)
+
+    signature = None
+
+    if privkeys:
+        click.echo("Signing with local private keys...", err=True)
+        signature = sign_with_privkeys(digest, privkeys)
+
+    if insert_signature:
+        click.echo("Inserting external signature...", err=True)
+        sigmask_str, signature = insert_signature
+        signature = bytes.fromhex(signature)
+        sigmask = 0
+        for bit in sigmask_str.split(":"):
+            sigmask |= 1 << (int(bit) - 1)
+
+    if signature:
+        fw.rehash()
+        fw.insert_signature(signature, sigmask)
+
+    click.echo(fw.format(verbose))
+
+    updated_data = fw.dump()
+    if updated_data == firmware_data:
+        click.echo("No changes made", err=True)
+    elif dry_run:
+        click.echo("Not saving changes", err=True)
+    else:
+        firmware_file.seek(0)
+        firmware_file.truncate(0)
+        firmware_file.write(updated_data)
+
+
+if __name__ == "__main__":
+    cli()
diff --git a/python/src/trezorlib/_internal/firmware_headers.py b/python/src/trezorlib/_internal/firmware_headers.py
new file mode 100644
index 0000000000..cf6e6daabb
--- /dev/null
+++ b/python/src/trezorlib/_internal/firmware_headers.py
@@ -0,0 +1,369 @@
+import struct
+from enum import Enum
+from typing import Any, List, Optional
+
+import click
+import construct as c
+import pyblake2
+
+from trezorlib import cosi, firmware
+
+SYM_OK = click.style("\u2714", fg="green")
+SYM_FAIL = click.style("\u274c", fg="red")
+
+
+class Status(Enum):
+    VALID = click.style("VALID", fg="green", bold=True)
+    INVALID = click.style("INVALID", fg="red", bold=True)
+    MISSING = click.style("MISSING", fg="blue", bold=True)
+    DEVEL = click.style("DEVEL", fg="red", bold=True)
+
+    def is_ok(self):
+        return self is Status.VALID or self is Status.DEVEL
+
+
+VHASH_DEVEL = bytes.fromhex(
+    "c5b4d40cb76911392122c8d1c277937e49c69b2aaf818001ec5c7663fcce258f"
+)
+
+
+AnyFirmware = c.Struct(
+    "vendor_header" / c.Optional(firmware.VendorHeader),
+    "image" / c.Optional(firmware.FirmwareImage),
+)
+
+
+class ImageType(Enum):
+    VENDOR_HEADER = 0
+    BOOTLOADER = 1
+    FIRMWARE = 2
+
+
+def _make_dev_keys(*key_bytes: bytes) -> List[bytes]:
+    return [k * 32 for k in key_bytes]
+
+
+def compute_vhash(vendor_header):
+    m = vendor_header.sig_m
+    n = vendor_header.sig_n
+    pubkeys = vendor_header.pubkeys
+    h = pyblake2.blake2s()
+    h.update(struct.pack("<BB", m, n))
+    for i in range(8):
+        if i < n:
+            h.update(pubkeys[i])
+        else:
+            h.update(b"\x00" * 32)
+    return h.digest()
+
+
+def all_zero(data: bytes) -> bool:
+    return all(b == 0 for b in data)
+
+
+def _check_signature_any(
+    header: c.Container, m: int, pubkeys: List[bytes], is_devel: bool
+) -> Optional[bool]:
+    if all_zero(header.signature) and header.sigmask == 0:
+        return Status.MISSING
+    try:
+        digest = firmware.header_digest(header)
+        cosi.verify(header.signature, digest, m, pubkeys, header.sigmask)
+        return Status.VALID if not is_devel else Status.DEVEL
+    except Exception:
+        return Status.INVALID
+
+
+# ====================== formatting functions ====================
+
+
+class LiteralStr(str):
+    pass
+
+
+def _format_container(
+    pb: c.Container,
+    indent: int = 0,
+    sep: str = " " * 4,
+    truncate_after: Optional[int] = 64,
+    truncate_to: Optional[int] = 32,
+) -> str:
+    def mostly_printable(bytes: bytes) -> bool:
+        if not bytes:
+            return True
+        printable = sum(1 for byte in bytes if 0x20 <= byte <= 0x7E)
+        return printable / len(bytes) > 0.8
+
+    def pformat(value: Any, indent: int) -> str:
+        level = sep * indent
+        leadin = sep * (indent + 1)
+
+        if isinstance(value, LiteralStr):
+            return value
+
+        if isinstance(value, list):
+            # short list of simple values
+            if not value or isinstance(value, (int, bool, Enum)):
+                return repr(value)
+
+            # long list, one line per entry
+            lines = ["[", level + "]"]
+            lines[1:1] = [leadin + pformat(x, indent + 1) for x in value]
+            return "\n".join(lines)
+
+        if isinstance(value, dict):
+            lines = ["{"]
+            for key, val in value.items():
+                if key.startswith("_"):
+                    continue
+                if val is None or val == []:
+                    continue
+                lines.append(leadin + key + ": " + pformat(val, indent + 1))
+            lines.append(level + "}")
+            return "\n".join(lines)
+
+        if isinstance(value, (bytes, bytearray)):
+            length = len(value)
+            suffix = ""
+            if truncate_after and length > truncate_after:
+                suffix = "..."
+                value = value[: truncate_to or 0]
+            if mostly_printable(value):
+                output = repr(value)
+            else:
+                output = value.hex()
+            return "{} bytes {}{}".format(length, output, suffix)
+
+        if isinstance(value, Enum):
+            return str(value)
+
+        return repr(value)
+
+    return pformat(pb, indent)
+
+
+def _format_version(version: c.Container) -> str:
+    version_str = ".".join(
+        str(version[k]) for k in ("major", "minor", "patch") if k in version
+    )
+    if "build" in version:
+        version_str += f" build {version.build}"
+    return version_str
+
+
+# =========================== functionality implementations ===============
+
+
+class SignableImage:
+    NAME = "Unrecognized image"
+    BIP32_INDEX = None
+    DEV_KEYS = []
+    DEV_KEY_SIGMASK = 0b11
+
+    def __init__(self, fw: c.Container) -> None:
+        self.fw = fw
+        self.header = None
+        self.public_keys = None
+        self.sigs_required = firmware.V2_SIGS_REQUIRED
+
+    def digest(self) -> bytes:
+        return firmware.header_digest(self.header)
+
+    def check_signature(self) -> Status:
+        raise NotImplementedError
+
+    def rehash(self) -> None:
+        raise NotImplementedError
+
+    def insert_signature(self, signature: bytes, sigmask: int) -> None:
+        self.header.signature = signature
+        self.header.sigmask = sigmask
+
+    def dump(self) -> bytes:
+        return AnyFirmware.build(self.fw)
+
+    def format(self, verbose: bool) -> str:
+        return _format_container(self.fw)
+
+
+class VendorHeader(SignableImage):
+    NAME = "vendorheader"
+    BIP32_INDEX = 1
+    DEV_KEYS = _make_dev_keys(b"\x44", b"\x45")
+
+    def __init__(self, fw):
+        super().__init__(fw)
+        self.header = fw.vendor_header
+        self.public_keys = firmware.V2_BOOTLOADER_KEYS
+
+    def check_signature(self) -> Status:
+        return _check_signature_any(
+            self.header, self.sigs_required, self.public_keys, False
+        )
+
+    def _format(self, terse: bool) -> str:
+        vh = self.fw.vendor_header
+        if not terse:
+            vhash = compute_vhash(vh)
+            output = [
+                "Vendor Header " + _format_container(vh),
+                f"Pubkey bundle hash: {vhash.hex()}",
+            ]
+        else:
+            output = [
+                "Vendor Header for {vendor} version {version} ({size} bytes)".format(
+                    vendor=click.style(vh.text, bold=True),
+                    version=_format_version(vh.version),
+                    size=vh.header_len,
+                ),
+            ]
+
+        fingerprint = firmware.header_digest(vh)
+
+        if not terse:
+            output.append(f"Fingerprint: {click.style(fingerprint.hex(), bold=True)}")
+
+        sig_status = self.check_signature()
+        sym = SYM_OK if sig_status.is_ok() else SYM_FAIL
+        output.append(f"{sym} Signature is {sig_status.value}")
+
+        return "\n".join(output)
+
+    def format(self, verbose: bool = False) -> str:
+        return self._format(terse=False)
+
+
+class BinImage(SignableImage):
+    def __init__(self, fw):
+        super().__init__(fw)
+        self.header = self.fw.image.header
+        self.code_hashes = firmware.calculate_code_hashes(
+            self.fw.image.code, self.fw.image._code_offset
+        )
+        self.digest_header = self.header.copy()
+        self.digest_header.hashes = self.code_hashes
+
+    def insert_signature(self, signature: bytes, sigmask: int) -> None:
+        super().insert_signature(signature, sigmask)
+        self.digest_header.signature = signature
+        self.digest_header.sigmask = sigmask
+
+    def digest(self) -> bytes:
+        return firmware.header_digest(self.digest_header)
+
+    def rehash(self):
+        self.header.hashes = self.code_hashes
+
+    def format(self, verbose: bool = False) -> str:
+        header_out = self.header.copy()
+
+        if not verbose:
+            for key in self.header:
+                if key.startswith("v1"):
+                    del header_out[key]
+                if "version" in key:
+                    header_out[key] = LiteralStr(_format_version(self.header[key]))
+
+        all_ok = SYM_OK
+        hash_status = Status.VALID
+        sig_status = Status.VALID
+
+        hashes_out = []
+        for expected, actual in zip(self.header.hashes, self.code_hashes):
+            status = SYM_OK if expected == actual else SYM_FAIL
+            hashes_out.append(LiteralStr(f"{status} {expected.hex()}"))
+
+        if all(all_zero(h) for h in self.header.hashes):
+            hash_status = Status.MISSING
+        elif self.header.hashes != self.code_hashes:
+            hash_status = Status.INVALID
+        else:
+            hash_status = Status.VALID
+
+        header_out["hashes"] = hashes_out
+
+        sig_status = self.check_signature()
+        all_ok = SYM_OK if hash_status.is_ok() and sig_status.is_ok() else SYM_FAIL
+
+        output = [
+            "Firmware Header " + _format_container(header_out),
+            f"Fingerprint: {click.style(self.digest().hex(), bold=True)}",
+            f"{all_ok} Signature is {sig_status.value}, hashes are {hash_status.value}",
+        ]
+
+        return "\n".join(output)
+
+
+class FirmwareImage(BinImage):
+    NAME = "firmware"
+    BIP32_INDEX = 2
+    DEV_KEYS = _make_dev_keys(b"\x47", b"\x48")
+
+    def __init__(self, fw: c.Container) -> None:
+        super().__init__(fw)
+        self.public_keys = fw.vendor_header.pubkeys
+        self.sigs_required = fw.vendor_header.sig_m
+
+    def check_signature(self) -> Status:
+        vhash = compute_vhash(self.fw.vendor_header)
+        return _check_signature_any(
+            self.digest_header,
+            self.sigs_required,
+            self.public_keys,
+            vhash == VHASH_DEVEL,
+        )
+
+    def format(self, verbose: bool = False) -> str:
+        return (
+            VendorHeader(self.fw)._format(terse=not verbose)
+            + "\n"
+            + super().format(verbose)
+        )
+
+
+class BootloaderImage(BinImage):
+    NAME = "bootloader"
+    BIP32_INDEX = 0
+    DEV_KEYS = _make_dev_keys(b"\x41", b"\x42")
+
+    def __init__(self, fw):
+        super().__init__(fw)
+        self._identify_dev_keys()
+
+    def insert_signature(self, signature: bytes, sigmask: int) -> None:
+        super().insert_signature(signature, sigmask)
+        self._identify_dev_keys()
+
+    def _identify_dev_keys(self):
+        # try checking signature with dev keys first
+        self.public_keys = firmware.V2_BOARDLOADER_DEV_KEYS
+        if not self.check_signature().is_ok():
+            # validation with dev keys failed, use production keys
+            self.public_keys = firmware.V2_BOARDLOADER_KEYS
+
+    def check_signature(self) -> Status:
+        return _check_signature_any(
+            self.header,
+            self.sigs_required,
+            self.public_keys,
+            self.public_keys == firmware.V2_BOARDLOADER_DEV_KEYS,
+        )
+
+
+def parse_image(image: bytes):
+    fw = AnyFirmware.parse(image)
+    if fw.vendor_header and not fw.image:
+        return VendorHeader(fw)
+    if (
+        not fw.vendor_header
+        and fw.image
+        and fw.image.header.magic == firmware.HeaderType.BOOTLOADER
+    ):
+        return BootloaderImage(fw)
+    if (
+        fw.vendor_header
+        and fw.image
+        and fw.image.header.magic == firmware.HeaderType.FIRMWARE
+    ):
+        return FirmwareImage(fw)
+    raise ValueError("Unrecognized image type")