diff options
author | JF <jf@codingfield.com> | 2021-03-07 18:45:35 +0100 |
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committer | Gitea <gitea@fake.local> | 2021-03-07 18:45:35 +0100 |
commit | c5dc4c55a79e0e3393df22e77825f24b6130a0bb (patch) | |
tree | 6f81eb191aa0c749cbef9b856d43ed4546302802 /tools/mcuboot/imgtool/keys/ecdsa.py | |
parent | ada942535718d48eec37cca4f50d678e7201dc67 (diff) | |
parent | 5845fd98ba68e12f1e57d50ed06abd7ccf47e029 (diff) |
Merge branch 'recovery-firmware' of JF/PineTime into develop
Diffstat (limited to 'tools/mcuboot/imgtool/keys/ecdsa.py')
-rw-r--r-- | tools/mcuboot/imgtool/keys/ecdsa.py | 157 |
1 files changed, 157 insertions, 0 deletions
diff --git a/tools/mcuboot/imgtool/keys/ecdsa.py b/tools/mcuboot/imgtool/keys/ecdsa.py new file mode 100644 index 00000000..139d583d --- /dev/null +++ b/tools/mcuboot/imgtool/keys/ecdsa.py @@ -0,0 +1,157 @@ +""" +ECDSA key management +""" + +from cryptography.hazmat.backends import default_backend +from cryptography.hazmat.primitives import serialization +from cryptography.hazmat.primitives.asymmetric import ec +from cryptography.hazmat.primitives.hashes import SHA256 + +from .general import KeyClass + +class ECDSAUsageError(Exception): + pass + +class ECDSA256P1Public(KeyClass): + def __init__(self, key): + self.key = key + + def shortname(self): + return "ecdsa" + + def _unsupported(self, name): + raise ECDSAUsageError("Operation {} requires private key".format(name)) + + def _get_public(self): + return self.key + + def get_public_bytes(self): + # The key is embedded into MBUboot in "SubjectPublicKeyInfo" format + return self._get_public().public_bytes( + encoding=serialization.Encoding.DER, + format=serialization.PublicFormat.SubjectPublicKeyInfo) + + def get_private_bytes(self, minimal): + self._unsupported('get_private_bytes') + + def export_private(self, path, passwd=None): + self._unsupported('export_private') + + def export_public(self, path): + """Write the public key to the given file.""" + pem = self._get_public().public_bytes( + encoding=serialization.Encoding.PEM, + format=serialization.PublicFormat.SubjectPublicKeyInfo) + with open(path, 'wb') as f: + f.write(pem) + + def sig_type(self): + return "ECDSA256_SHA256" + + def sig_tlv(self): + return "ECDSA256" + + def sig_len(self): + # Early versions of MCUboot (< v1.5.0) required ECDSA + # signatures to be padded to 72 bytes. Because the DER + # encoding is done with signed integers, the size of the + # signature will vary depending on whether the high bit is set + # in each value. This padding was done in a + # not-easily-reversible way (by just adding zeros). + # + # The signing code no longer requires this padding, and newer + # versions of MCUboot don't require it. But, continue to + # return the total length so that the padding can be done if + # requested. + return 72 + + def verify(self, signature, payload): + # strip possible paddings added during sign + signature = signature[:signature[1] + 2] + k = self.key + if isinstance(self.key, ec.EllipticCurvePrivateKey): + k = self.key.public_key() + return k.verify(signature=signature, data=payload, + signature_algorithm=ec.ECDSA(SHA256())) + + +class ECDSA256P1(ECDSA256P1Public): + """ + Wrapper around an ECDSA private key. + """ + + def __init__(self, key): + """key should be an instance of EllipticCurvePrivateKey""" + self.key = key + self.pad_sig = False + + @staticmethod + def generate(): + pk = ec.generate_private_key( + ec.SECP256R1(), + backend=default_backend()) + return ECDSA256P1(pk) + + def _get_public(self): + return self.key.public_key() + + def _build_minimal_ecdsa_privkey(self, der): + ''' + Builds a new DER that only includes the EC private key, removing the + public key that is added as an "optional" BITSTRING. + ''' + offset_PUB = 68 + EXCEPTION_TEXT = "Error parsing ecdsa key. Please submit an issue!" + if der[offset_PUB] != 0xa1: + raise ECDSAUsageError(EXCEPTION_TEXT) + len_PUB = der[offset_PUB + 1] + b = bytearray(der[:-offset_PUB]) + offset_SEQ = 29 + if b[offset_SEQ] != 0x30: + raise ECDSAUsageError(EXCEPTION_TEXT) + b[offset_SEQ + 1] -= len_PUB + offset_OCT_STR = 27 + if b[offset_OCT_STR] != 0x04: + raise ECDSAUsageError(EXCEPTION_TEXT) + b[offset_OCT_STR + 1] -= len_PUB + if b[0] != 0x30 or b[1] != 0x81: + raise ECDSAUsageError(EXCEPTION_TEXT) + b[2] -= len_PUB + return b + + def get_private_bytes(self, minimal): + priv = self.key.private_bytes( + encoding=serialization.Encoding.DER, + format=serialization.PrivateFormat.PKCS8, + encryption_algorithm=serialization.NoEncryption()) + if minimal: + priv = self._build_minimal_ecdsa_privkey(priv) + return priv + + def export_private(self, path, passwd=None): + """Write the private key to the given file, protecting it with the optional password.""" + if passwd is None: + enc = serialization.NoEncryption() + else: + enc = serialization.BestAvailableEncryption(passwd) + pem = self.key.private_bytes( + encoding=serialization.Encoding.PEM, + format=serialization.PrivateFormat.PKCS8, + encryption_algorithm=enc) + with open(path, 'wb') as f: + f.write(pem) + + def raw_sign(self, payload): + """Return the actual signature""" + return self.key.sign( + data=payload, + signature_algorithm=ec.ECDSA(SHA256())) + + def sign(self, payload): + sig = self.raw_sign(payload) + if self.pad_sig: + # To make fixed length, pad with one or two zeros. + sig += b'\000' * (self.sig_len() - len(sig)) + return sig + else: + return sig |