api/bootloader: add ParseSignedFirwmare() util function

Author: benma

api/bootloader/device.go

@@ -233,18 +233,12 @@ func (device *Device) flashUnsignedFirmware(firmware []byte, progressCallback fu
 // format is invalid, or the firmware magic does not match the expected magic according to the
 // device product.
 func (device *Device) parseSignedFirmware(firmware []byte) ([]byte, []byte, error) {
-	if len(firmware) <= magicLen+sigDataLen {
-		return nil, nil, errp.New("firmware too small")
-	}
-	magic, firmware := firmware[:magicLen], firmware[magicLen:]
-	sigData, firmware := firmware[:sigDataLen], firmware[sigDataLen:]
-
-	expectedMagic, ok := sigDataMagic[device.product]
-	if !ok {
-		return nil, nil, errp.New("unrecognized product")
+	product, sigData, firmware, err := ParseSignedFirmware(firmware)
+	if err != nil {
+		return nil, nil, err
 	}
-	if binary.BigEndian.Uint32(magic) != expectedMagic {
-		return nil, nil, errp.New("invalid signing pubkeys data magic")
+	if product != device.product {
+		return nil, nil, errp.New("signed firmware binary does not match device product")
 	}
 	return sigData, firmware, nil
 }

api/bootloader/util.go

@@ -18,6 +18,9 @@ import (
 	"bytes"
 	"crypto/sha256"
 	"encoding/binary"
+
+	"github.com/digitalbitbox/bitbox02-api-go/api/common"
+	"github.com/digitalbitbox/bitbox02-api-go/util/errp"
 )
 
 // HashFirmware returns the hash of `<firmware version><firmware>`, as computed by the bootloader to
@@ -35,3 +38,28 @@ func HashFirmware(firmwareVersion uint32, unsignedFirmware []byte) []byte {
 	copy(padded, unsignedFirmware)
 	return doubleHash(append(firmwareVersionLE, padded...))
 }
+
+// ParseSignedFirmware parses a signed firmware file and returns (sigdata, firmware). Errors if the
+// format is invalid, or the firmware magic does not match the expected magic according to the
+// device product.
+func ParseSignedFirmware(firmware []byte) (common.Product, []byte, []byte, error) {
+	if len(firmware) <= magicLen+sigDataLen {
+		return "", nil, nil, errp.New("firmware too small")
+	}
+	magic, firmware := firmware[:magicLen], firmware[magicLen:]
+	sigData, firmware := firmware[:sigDataLen], firmware[sigDataLen:]
+
+	var product common.Product
+	magicInt := binary.BigEndian.Uint32(magic)
+	for p, productMagic := range sigDataMagic {
+		if magicInt == productMagic {
+			product = p
+			break
+		}
+	}
+	if product == "" {
+		return "", nil, nil, errp.Newf("unrecognized magic")
+	}
+
+	return product, sigData, firmware, nil
+}

api/bootloader/util_test.go

@@ -15,9 +15,11 @@
 package bootloader
 
 import (
+	"encoding/hex"
 	"io/ioutil"
 	"testing"
 
+	"github.com/digitalbitbox/bitbox02-api-go/api/common"
 	"github.com/stretchr/testify/require"
 )
 
@@ -32,3 +34,25 @@ func TestHashFirmware(t *testing.T) {
 		HashFirmware(7, unsignedFirmware),
 	)
 }
+
+func TestParseSignedFirmmare(t *testing.T) {
+	unsignedFirmware, err := ioutil.ReadFile("testdata/firmware-btc.v4.2.2.bin")
+	require.NoError(t, err)
+
+	signedFirmware, err := ioutil.ReadFile("testdata/firmware-btc.v4.2.2.signed.bin")
+	require.NoError(t, err)
+
+	product, sigData, firmware, err := ParseSignedFirmware(signedFirmware)
+	require.NoError(t, err)
+
+	expectedSigData := "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"
+	require.Equal(t, expectedSigData, hex.EncodeToString(sigData))
+	require.Equal(t, common.ProductBitBox02BTCOnly, product)
+	require.Equal(t, unsignedFirmware, firmware)
+
+	// Test invalid magic
+	signedFirmware[0] = 0
+	_, _, _, err = ParseSignedFirmware(signedFirmware)
+	require.Error(t, err)
+
+}