signing.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
import argparse
import hashlib
import os
import struct
import subprocess
import sys

def parse_args():
    parser = argparse.ArgumentParser(description='Binary signing tool')
    parser.add_argument('-m', '--mode', help='Mode (header, sign)')
    parser.add_argument('-b', '--bin', help='Unsigned binary')
    parser.add_argument('-o', '--out', help='Output file');
    parser.add_argument('-l', '--legacy', help='Legacy output file');
    parser.add_argument('-p', '--publickey', help='Public key file');
    parser.add_argument('-s', '--privatekey', help='Private(secret) key file');
    return parser.parse_args()

def sign_and_write(data, priv_key, out_file):
    """Signs the data (bytes) with the private key (file path)."""
    """Save the signed firmware to out_file (file path)."""

    signcmd = [ 'openssl', 'dgst', '-sha256', '-sign', priv_key ]
    proc = subprocess.Popen(signcmd, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
    signout, signerr = proc.communicate(input=data)
    if proc.returncode:
        sys.stderr.write("OpenSSL returned an error signing the binary: " + str(proc.returncode) + "\nSTDERR: " + str(signerr))
    else:
        with open(out_file, "wb") as out:
            out.write(data)
            out.write(signout)
            out.write(struct.pack("<L", len(signout))) # u32, little-endian
            sys.stderr.write("Signed binary: " + out_file + "\n")

def sign_and_write_legacy(data, priv_key, out_file):
    """Signs the data (bytes) with the private key (file path)."""
    """Save the signed firmware to out_file (file path)."""

    sha256 = hashlib.sha256(data)
    signcmd = [ 'openssl', 'rsautl', '-sign', '-inkey', priv_key ]
    proc = subprocess.Popen(signcmd, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
    signout, signerr = proc.communicate(input=sha256.digest())
    if proc.returncode:
        sys.stderr.write("OpenSSL returned an error legacy signing the binary: " + str(proc.returncode) + "\nSTDERR: " + str(signerr))
    else:
        with open(out_file, "wb") as out:
            out.write(data)
            out.write(signout)
            out.write(struct.pack("<L", len(signout))) # u32, little-endian
            sys.stderr.write("Legacy signed binary: " + out_file + "\n")

def main():
    args = parse_args()
    if args.mode == "header":
        val = ""
        try:
            with open(args.publickey, "rb") as f:
                pub = f.read()
                val += "#include <pgmspace.h>\n"
                val += "#define ARDUINO_SIGNING 1\n"
                val += "static const char signing_pubkey[] PROGMEM = {\n"
                for i in bytearray(pub):
                    val += "0x%02x, \n" % i
                val = val[:-3]
                val +="\n};\n"
                sys.stderr.write("Enabling binary signing\n")
        except IOError:
# Silence the default case to avoid people thinking something is wrong.
# Only people who care about signing will know what it means, anyway,
# and they can check for the positive acknowledgement above.
#            sys.stderr.write("Not enabling binary signing\n")
            val += "#define ARDUINO_SIGNING 0\n"
        outdir = os.path.dirname(args.out)
        if not os.path.exists(outdir):
            os.makedirs(outdir)
        try:
            with open(args.out, "r") as inp:
                old_val = inp.read()
                if old_val == val:
                    return
        except Exception:
            pass
        with open(args.out, "w") as f:
            f.write(val)
        return 0
    elif args.mode == "sign":
        if not os.path.isfile(args.privatekey):
            return
        try:
            with open(args.bin, "rb") as b:
                bin = b.read()

                sign_and_write(bin, args.privatekey, args.out)

                if args.legacy:
                    sign_and_write_legacy(bin, args.privatekey, args.legacy)

        except Exception as e:
            sys.stderr.write(str(e))
            sys.stderr.write("Not signing the generated binary\n")
        return 0
    else:
        sys.stderr.write("ERROR: Mode not specified as header or sign\n")

if __name__ == '__main__':
    sys.exit(main())