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kntran1
289
bootloader/mcuboot/scripts/imgtool/keys/ecdsa.py
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289
bootloader/mcuboot/scripts/imgtool/keys/ecdsa.py
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"""
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ECDSA key management
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"""
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# SPDX-License-Identifier: Apache-2.0
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import os.path
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import hashlib
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import serialization
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from cryptography.hazmat.primitives.asymmetric import ec
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from cryptography.hazmat.primitives.hashes import SHA256, SHA384
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from .general import KeyClass
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from .privatebytes import PrivateBytesMixin
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class ECDSAUsageError(Exception):
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pass
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class ECDSAPublicKey(KeyClass):
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"""
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Wrapper around an ECDSA public key.
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"""
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def __init__(self, key):
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self.key = key
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def _unsupported(self, name):
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raise ECDSAUsageError("Operation {} requires private key".format(name))
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def _get_public(self):
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return self.key
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def get_public_bytes(self):
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# The key is embedded into MBUboot in "SubjectPublicKeyInfo" format
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return self._get_public().public_bytes(
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encoding=serialization.Encoding.DER,
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format=serialization.PublicFormat.SubjectPublicKeyInfo)
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def get_public_pem(self):
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return self._get_public().public_bytes(
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encoding=serialization.Encoding.PEM,
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format=serialization.PublicFormat.SubjectPublicKeyInfo)
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def get_private_bytes(self, minimal, format):
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self._unsupported('get_private_bytes')
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def export_private(self, path, passwd=None):
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self._unsupported('export_private')
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def export_public(self, path):
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"""Write the public key to the given file."""
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pem = self._get_public().public_bytes(
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encoding=serialization.Encoding.PEM,
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format=serialization.PublicFormat.SubjectPublicKeyInfo)
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with open(path, 'wb') as f:
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f.write(pem)
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class ECDSAPrivateKey(PrivateBytesMixin):
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"""
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Wrapper around an ECDSA private key.
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"""
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def __init__(self, key):
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self.key = key
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def _get_public(self):
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return self.key.public_key()
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def _build_minimal_ecdsa_privkey(self, der, format):
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'''
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Builds a new DER that only includes the EC private key, removing the
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public key that is added as an "optional" BITSTRING.
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'''
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if format == serialization.PrivateFormat.OpenSSH:
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print(os.path.basename(__file__) +
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': Warning: --minimal is supported only for PKCS8 '
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'or TraditionalOpenSSL formats')
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return bytearray(der)
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EXCEPTION_TEXT = "Error parsing ecdsa key. Please submit an issue!"
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if format == serialization.PrivateFormat.PKCS8:
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offset_PUB = 68 # where the context specific TLV starts (tag 0xA1)
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if der[offset_PUB] != 0xa1:
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raise ECDSAUsageError(EXCEPTION_TEXT)
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len_PUB = der[offset_PUB + 1] + 2 # + 2 for 0xA1 0x44 bytes
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b = bytearray(der[:offset_PUB]) # remove the TLV with the PUB key
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offset_SEQ = 29
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if b[offset_SEQ] != 0x30:
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raise ECDSAUsageError(EXCEPTION_TEXT)
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b[offset_SEQ + 1] -= len_PUB
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offset_OCT_STR = 27
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if b[offset_OCT_STR] != 0x04:
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raise ECDSAUsageError(EXCEPTION_TEXT)
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b[offset_OCT_STR + 1] -= len_PUB
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if b[0] != 0x30 or b[1] != 0x81:
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raise ECDSAUsageError(EXCEPTION_TEXT)
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# as b[1] has bit7 set, the length is on b[2]
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b[2] -= len_PUB
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if b[2] < 0x80:
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del(b[1])
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elif format == serialization.PrivateFormat.TraditionalOpenSSL:
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offset_PUB = 51
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if der[offset_PUB] != 0xA1:
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raise ECDSAUsageError(EXCEPTION_TEXT)
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len_PUB = der[offset_PUB + 1] + 2
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b = bytearray(der[0:offset_PUB])
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b[1] -= len_PUB
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return b
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_VALID_FORMATS = {
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'pkcs8': serialization.PrivateFormat.PKCS8,
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'openssl': serialization.PrivateFormat.TraditionalOpenSSL
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}
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_DEFAULT_FORMAT = 'pkcs8'
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def get_private_bytes(self, minimal, format):
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format, priv = self._get_private_bytes(minimal,
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format, ECDSAUsageError)
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if minimal:
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priv = self._build_minimal_ecdsa_privkey(
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priv, self._VALID_FORMATS[format])
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return priv
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def export_private(self, path, passwd=None):
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"""Write the private key to the given file, protecting it with '
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'the optional password."""
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if passwd is None:
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enc = serialization.NoEncryption()
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else:
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enc = serialization.BestAvailableEncryption(passwd)
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pem = self.key.private_bytes(
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encoding=serialization.Encoding.PEM,
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format=serialization.PrivateFormat.PKCS8,
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encryption_algorithm=enc)
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with open(path, 'wb') as f:
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f.write(pem)
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class ECDSA256P1Public(ECDSAPublicKey):
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"""
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Wrapper around an ECDSA (p256) public key.
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"""
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def __init__(self, key):
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super().__init__(key)
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self.key = key
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def shortname(self):
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return "ecdsa"
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def sig_type(self):
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return "ECDSA256_SHA256"
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def sig_tlv(self):
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return "ECDSASIG"
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def sig_len(self):
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# Early versions of MCUboot (< v1.5.0) required ECDSA
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# signatures to be padded to 72 bytes. Because the DER
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# encoding is done with signed integers, the size of the
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# signature will vary depending on whether the high bit is set
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# in each value. This padding was done in a
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# not-easily-reversible way (by just adding zeros).
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#
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# The signing code no longer requires this padding, and newer
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# versions of MCUboot don't require it. But, continue to
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# return the total length so that the padding can be done if
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# requested.
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return 72
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def verify(self, signature, payload):
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# strip possible paddings added during sign
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signature = signature[:signature[1] + 2]
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k = self.key
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if isinstance(self.key, ec.EllipticCurvePrivateKey):
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k = self.key.public_key()
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return k.verify(signature=signature, data=payload,
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signature_algorithm=ec.ECDSA(SHA256()))
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class ECDSA256P1(ECDSAPrivateKey, ECDSA256P1Public):
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"""
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Wrapper around an ECDSA (p256) private key.
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"""
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def __init__(self, key):
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super().__init__(key)
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self.key = key
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self.pad_sig = False
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@staticmethod
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def generate():
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pk = ec.generate_private_key(
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ec.SECP256R1(),
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backend=default_backend())
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return ECDSA256P1(pk)
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def raw_sign(self, payload):
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"""Return the actual signature"""
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return self.key.sign(
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data=payload,
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signature_algorithm=ec.ECDSA(SHA256()))
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def sign(self, payload):
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sig = self.raw_sign(payload)
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if self.pad_sig:
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# To make fixed length, pad with one or two zeros.
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sig += b'\000' * (self.sig_len() - len(sig))
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return sig
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else:
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return sig
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class ECDSA384P1Public(ECDSAPublicKey):
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"""
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Wrapper around an ECDSA (p384) public key.
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"""
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def __init__(self, key):
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super().__init__(key)
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self.key = key
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def shortname(self):
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return "ecdsap384"
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def sig_type(self):
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return "ECDSA384_SHA384"
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def sig_tlv(self):
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return "ECDSASIG"
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def sig_len(self):
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# Early versions of MCUboot (< v1.5.0) required ECDSA
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# signatures to be padded to a fixed length. Because the DER
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# encoding is done with signed integers, the size of the
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# signature will vary depending on whether the high bit is set
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# in each value. This padding was done in a
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# not-easily-reversible way (by just adding zeros).
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#
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# The signing code no longer requires this padding, and newer
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# versions of MCUboot don't require it. But, continue to
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# return the total length so that the padding can be done if
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# requested.
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return 103
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def verify(self, signature, payload):
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# strip possible paddings added during sign
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signature = signature[:signature[1] + 2]
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k = self.key
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if isinstance(self.key, ec.EllipticCurvePrivateKey):
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k = self.key.public_key()
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return k.verify(signature=signature, data=payload,
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signature_algorithm=ec.ECDSA(SHA384()))
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class ECDSA384P1(ECDSAPrivateKey, ECDSA384P1Public):
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"""
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Wrapper around an ECDSA (p384) private key.
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"""
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def __init__(self, key):
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"""key should be an instance of EllipticCurvePrivateKey"""
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super().__init__(key)
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self.key = key
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self.pad_sig = False
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@staticmethod
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def generate():
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pk = ec.generate_private_key(
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ec.SECP384R1(),
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backend=default_backend())
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return ECDSA384P1(pk)
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def raw_sign(self, payload):
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"""Return the actual signature"""
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return self.key.sign(
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data=payload,
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signature_algorithm=ec.ECDSA(SHA384()))
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def sign(self, payload):
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sig = self.raw_sign(payload)
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if self.pad_sig:
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# To make fixed length, pad with one or two zeros.
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sig += b'\000' * (self.sig_len() - len(sig))
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return sig
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else:
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return sig
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