103 lines
3.2 KiB
Python
103 lines
3.2 KiB
Python
"""
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ECDSA key management
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"""
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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
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from .general import KeyClass
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class ECDSAUsageError(Exception):
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pass
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class ECDSA256P1Public(KeyClass):
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def __init__(self, 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 _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 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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def sig_type(self):
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return "ECDSA256_SHA256"
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def sig_tlv(self):
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return "ECDSA256"
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def sig_len(self):
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# The DER encoding depends on the high bit, and can be
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# anywhere from 70 to 72 bytes. Because we have to fill in
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# the length field before computing the signature, however,
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# we'll give the largest, and the sig checking code will allow
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# for it to be up to two bytes larger than the actual
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# signature.
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return 72
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class ECDSA256P1(ECDSA256P1Public):
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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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"""key should be an instance of EllipticCurvePrivateKey"""
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self.key = key
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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 _get_public(self):
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return self.key.public_key()
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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 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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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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# To make fixed length, pad with one or two zeros.
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sig = self.raw_sign(payload)
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sig += b'\000' * (self.sig_len() - len(sig))
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return sig
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