From 7a3b2605ac5327edfb51da6009604fbc33957fb9 Mon Sep 17 00:00:00 2001 From: Fabio Utzig Date: Tue, 22 Oct 2019 09:56:44 -0300 Subject: [PATCH] imgtool: add creation of ECIES-P256 encrypted images Signed-off-by: Fabio Utzig --- scripts/imgtool/image.py | 44 ++++++++++++++++++++++++++++++++-------- scripts/imgtool/main.py | 12 ++++++----- 2 files changed, 43 insertions(+), 13 deletions(-) diff --git a/scripts/imgtool/image.py b/scripts/imgtool/image.py index cfc9b7cc..e2461c22 100644 --- a/scripts/imgtool/image.py +++ b/scripts/imgtool/image.py @@ -24,10 +24,13 @@ from intelhex import IntelHex import hashlib import struct import os.path -from cryptography.hazmat.primitives.asymmetric import padding +from .keys import rsa, ecdsa +from cryptography.hazmat.primitives.asymmetric import ec, padding from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes +from cryptography.hazmat.primitives.kdf.hkdf import HKDF +from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat from cryptography.hazmat.backends import default_backend -from cryptography.hazmat.primitives import hashes +from cryptography.hazmat.primitives import hashes, hmac from cryptography.exceptions import InvalidSignature IMAGE_MAGIC = 0x96f3b83d @@ -56,6 +59,7 @@ TLV_VALUES = { 'ED25519': 0x24, 'ENCRSA2048': 0x30, 'ENCKW128': 0x31, + 'ENCEC256': 0x32, 'DEPENDENCY': 0x40 } @@ -209,6 +213,25 @@ class Image(): len(self.payload), tsize, self.slot_size) raise Exception(msg) + def ecies_p256_hkdf(self, enckey, plainkey): + newpk = ec.generate_private_key(ec.SECP256R1(), default_backend()) + shared = newpk.exchange(ec.ECDH(), enckey._get_public()) + derived_key = HKDF( + algorithm=hashes.SHA256(), length=48, salt=None, + info=b'MCUBoot_ECIES_v1', backend=default_backend()).derive(shared) + encryptor = Cipher(algorithms.AES(derived_key[:16]), + modes.CTR(bytes([0] * 16)), + backend=default_backend()).encryptor() + cipherkey = encryptor.update(plainkey) + encryptor.finalize() + mac = hmac.HMAC(derived_key[16:], hashes.SHA256(), + backend=default_backend()) + mac.update(cipherkey) + ciphermac = mac.finalize() + pubk = newpk.public_key().public_bytes( + encoding=Encoding.X962, + format=PublicFormat.UncompressedPoint) + return cipherkey, ciphermac, pubk + def create(self, key, enckey, dependencies=None): self.enckey = enckey @@ -279,12 +302,17 @@ class Image(): if enckey is not None: plainkey = os.urandom(16) - cipherkey = enckey._get_public().encrypt( - plainkey, padding.OAEP( - mgf=padding.MGF1(algorithm=hashes.SHA256()), - algorithm=hashes.SHA256(), - label=None)) - tlv.add('ENCRSA2048', cipherkey) + + if isinstance(enckey, rsa.RSAPublic): + cipherkey = enckey._get_public().encrypt( + plainkey, padding.OAEP( + mgf=padding.MGF1(algorithm=hashes.SHA256()), + algorithm=hashes.SHA256(), + label=None)) + tlv.add('ENCRSA2048', cipherkey) + elif isinstance(enckey, ecdsa.ECDSA256P1Public): + cipherkey, mac, pubk = self.ecies_p256_hkdf(enckey, plainkey) + tlv.add('ENCEC256', pubk + mac + cipherkey) nonce = bytes([0] * 16) cipher = Cipher(algorithms.AES(plainkey), modes.CTR(nonce), diff --git a/scripts/imgtool/main.py b/scripts/imgtool/main.py index 2b0d4feb..53c3c0f7 100755 --- a/scripts/imgtool/main.py +++ b/scripts/imgtool/main.py @@ -226,11 +226,13 @@ def sign(key, align, version, header_size, pad_header, slot_size, pad, img.load(infile) key = load_key(key) if key else None enckey = load_key(encrypt) if encrypt else None - if enckey: - if not isinstance(enckey, (keys.RSA, keys.RSAPublic)): - raise Exception("Encryption only available with RSA key") - if key and not isinstance(key, keys.RSA): - raise Exception("Signing only available with private RSA key") + if enckey and key: + if ((isinstance(key, keys.ECDSA256P1) and + not isinstance(enckey, keys.ECDSA256P1Public)) + or (isinstance(key, keys.RSA) and + not isinstance(enckey, keys.RSAPublic))): + # FIXME + raise Exception("Signing and encryption must use the same type of key") img.create(key, enckey, dependencies) img.save(outfile, hex_addr)