96 lines
2.9 KiB
Python
96 lines
2.9 KiB
Python
"""
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RSA 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 rsa
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from cryptography.hazmat.primitives.asymmetric.padding import PSS, MGF1
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from cryptography.hazmat.primitives.hashes import SHA256
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from .general import KeyClass
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class RSAUsageError(Exception):
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pass
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class RSA2048Public(KeyClass):
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"""The public key can only do a few operations"""
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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 "rsa"
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def _unsupported(self, name):
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raise RSAUsageError("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 embedded into MCUboot is in PKCS1 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.PKCS1)
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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 "PKCS1_PSS_RSA2048_SHA256"
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def sig_tlv(self):
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return "RSA2048"
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def sig_len(self):
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return 256
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class RSA2048(RSA2048Public):
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"""
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Wrapper around an 2048-bit RSA key, with imgtool support.
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"""
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def __init__(self, key):
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"""The key should be a private key from cryptography"""
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self.key = key
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@staticmethod
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def generate():
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pk = rsa.generate_private_key(
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public_exponent=65537,
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key_size=2048,
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backend=default_backend())
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return RSA2048(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 sign(self, payload):
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# The verification code only allows the salt length to be the
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# same as the hash length, 32.
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return self.key.sign(
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data=payload,
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padding=PSS(mgf=MGF1(SHA256()), salt_length=32),
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algorithm=SHA256())
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