initial commit

.gitignore

@@ -0,0 +1,2 @@
+/.idea
+/*.sh

cmd/tesla-firmware-decrypt/main.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"encoding/base64"
+	"github.com/alexflint/go-arg"
+	"github.com/denysvitali/tesla-firmware-decrypt/pkg"
+	"github.com/sirupsen/logrus"
+	"os"
+)
+
+var args struct {
+	InputFile string `arg:"positional,required"`
+	Key       string `arg:"-k,required"`
+}
+
+var logger = logrus.New()
+
+func main() {
+	arg.MustParse(&args)
+	f, err := os.Open(args.InputFile)
+	if err != nil {
+		logger.Fatalf("unable to open file: %v", err)
+	}
+
+	keyBytes, err := base64.StdEncoding.DecodeString(args.Key)
+	if err != nil {
+		logger.Fatalf("unable to decode base64 key: %v", err)
+	}
+	if len(keyBytes) != 32 {
+		logger.Fatalf("invalid key size: expected 32 but received %d", len(keyBytes))
+	}
+
+	dec := decrypt.Decrypt{
+		Key: keyBytes,
+	}
+	err = dec.Decrypt(f, os.Stdout)
+	if err != nil {
+		logger.Fatalf("unable to decrypt: %v", err)
+	}
+}

go.mod

@@ -0,0 +1,12 @@
+module github.com/denysvitali/tesla-firmware-decrypt
+
+go 1.19
+
+require golang.org/x/crypto v0.3.0
+
+require (
+	github.com/alexflint/go-arg v1.4.3 // indirect
+	github.com/alexflint/go-scalar v1.1.0 // indirect
+	github.com/sirupsen/logrus v1.9.0 // indirect
+	golang.org/x/sys v0.2.0 // indirect
+)

go.sum

@@ -0,0 +1,19 @@
+github.com/alexflint/go-arg v1.4.3 h1:9rwwEBpMXfKQKceuZfYcwuc/7YY7tWJbFsgG5cAU/uo=
+github.com/alexflint/go-arg v1.4.3/go.mod h1:3PZ/wp/8HuqRZMUUgu7I+e1qcpUbvmS258mRXkFH4IA=
+github.com/alexflint/go-scalar v1.1.0 h1:aaAouLLzI9TChcPXotr6gUhq+Scr8rl0P9P4PnltbhM=
+github.com/alexflint/go-scalar v1.1.0/go.mod h1:LoFvNMqS1CPrMVltza4LvnGKhaSpc3oyLEBUZVhhS2o=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
+github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/crypto v0.3.0 h1:a06MkbcxBrEFc0w0QIZWXrH/9cCX6KJyWbBOIwAn+7A=
+golang.org/x/crypto v0.3.0/go.mod h1:hebNnKkNXi2UzZN1eVRvBB7co0a+JxK6XbPiWVs/3J4=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.2.0 h1:ljd4t30dBnAvMZaQCevtY0xLLD0A+bRZXbgLMLU1F/A=
+golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

pkg/decrypt.go

@@ -0,0 +1,38 @@
+package decrypt
+
+import (
+	"encoding/binary"
+	"fmt"
+	"golang.org/x/crypto/salsa20"
+	"io"
+)
+
+type Decrypt struct {
+	Key []byte
+}
+
+func (d *Decrypt) Decrypt(reader io.Reader, writer io.Writer) error {
+	if len(d.Key) != 32 {
+		return fmt.Errorf("key must be 32 bytes long")
+	}
+	blockNumber := 0
+	for {
+		nonceBytes := make([]byte, 24)
+		binary.LittleEndian.PutUint64(nonceBytes, uint64(blockNumber))
+		block := make([]byte, 256)
+		_, err := reader.Read(block)
+		if err == io.EOF {
+			return nil
+		}
+		if err != nil {
+			return fmt.Errorf("unable to read file: %v", err)
+		}
+		outBlock := make([]byte, 256)
+		salsa20.XORKeyStream(outBlock, block, nonceBytes, (*[32]byte)(d.Key))
+		blockNumber++
+		_, err = writer.Write(outBlock)
+		if err != nil {
+			return fmt.Errorf("unable to write: %v", err)
+		}
+	}
+}

pkg/decrypt_test.go

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+package decrypt_test
+
+import (
+	"bytes"
+	"encoding/base64"
+	"os"
+	decrypt "tesla-firmware-decrypt/pkg"
+	"testing"
+)
+
+func TestDecrypt_Decrypt(t *testing.T) {
+	ciphertext, err := os.Open("./resources/1_0.bin")
+	if err != nil {
+		t.Fatalf("unable to open file: %v", err)
+	}
+
+	key := "uPaonw9KIv1tptQ3hsJsrR2Ibz3YhOcBRBaRitSi4Qg="
+	keyBytes, err := base64.StdEncoding.DecodeString(key)
+	if err != nil {
+		t.Fatalf("unable to decode base64: %v", err)
+	}
+	d := decrypt.Decrypt{Key: keyBytes}
+
+	buffer := bytes.NewBuffer(nil)
+	err = d.Decrypt(ciphertext, buffer)
+
+	if err != nil {
+		t.Fatalf("unable to decrypt: %v", err)
+	}
+
+	expectedHeader := []byte("hsqs")
+	header := make([]byte, len(expectedHeader))
+	_, err = buffer.Read(header)
+	if err != nil {
+		t.Fatalf("unable to read into buffer: %v", err)
+	}
+
+	if !bytes.Equal(expectedHeader, header) {
+		t.Fatalf("decryption failed: got %s but %s was expected", header, expectedHeader)
+	}
+}

py/main.py

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+import base64
+import tempfile
+
+import click
+import salsa20
+
+
+@click.command()
+@click.option("-i", "--input", required=True)
+@click.option("-k", "--key", required=True)
+def cmd(input: str, key: str):
+    tmp = tempfile.mktemp()
+    print(tmp)
+
+    with open(tmp, mode="wb") as tmp_out:
+        with open(input, mode="rb") as f:
+            counter = 0
+            key_bytes = base64.b64decode(key)
+            while True:
+                in_bytes = f.read(256)
+                if len(in_bytes) == 0:
+                    return
+                counter_bytes = counter.to_bytes(24, byteorder='little')
+                res = salsa20.XSalsa20_xor(in_bytes, counter_bytes, key_bytes)
+                tmp_out.write(res)
+                counter += 1
+
+if __name__ == "__main__":
+    cmd()

resources/1_0.bin

@@ -0,0 +1 @@
+ƒf²Ø²ø÷¨t[$šëØs©¶IRHBÑ%ô8,OÑy÷ò©]¿‹i¸lòˆ»˜´A‚ÖSú;-‘4TfS†¢¾¶Vý]´…™/¸úP…ûZ~øez’þÀœE–Ê»|©gì|<7C>ëB“ÿeñïŽ1zîzÏ£»DfòœD%(`bÀõÔAÐÒ™"XwÒ¬<>‹±xÔèŽN!\¾Ü™T'FaÊêLÔÄ`¹á7J#à’¯yÖ—è°…9<E280A6>Î×<C38E>“è