[Add] First commit

scripts/imgtool/imglib/keys/rsa.py

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+"""
+RSA Key management
+"""
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.primitives.asymmetric.padding import PSS, MGF1
+from cryptography.hazmat.primitives.hashes import SHA256
+
+from .general import KeyClass
+
+class RSAUsageError(Exception):
+    pass
+
+class RSA2048Public(KeyClass):
+    """The public key can only do a few operations"""
+    def __init__(self, key):
+        self.key = key
+
+    def shortname(self):
+        return "rsa"
+
+    def _unsupported(self, name):
+        raise RSAUsageError("Operation {} requires private key".format(name))
+
+    def _get_public(self):
+        return self.key
+
+    def get_public_bytes(self):
+        # The key embedded into MCUboot is in PKCS1 format.
+        return self._get_public().public_bytes(
+                encoding=serialization.Encoding.DER,
+                format=serialization.PublicFormat.PKCS1)
+
+    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 "PKCS1_PSS_RSA2048_SHA256"
+
+    def sig_tlv(self):
+        return "RSA2048"
+
+    def sig_len(self):
+        return 256
+
+class RSA2048(RSA2048Public):
+    """
+    Wrapper around an 2048-bit RSA key, with imgtool support.
+    """
+
+    def __init__(self, key):
+        """The key should be a private key from cryptography"""
+        self.key = key
+
+    @staticmethod
+    def generate():
+        pk = rsa.generate_private_key(
+                public_exponent=65537,
+                key_size=2048,
+                backend=default_backend())
+        return RSA2048(pk)
+
+    def _get_public(self):
+        return self.key.public_key()
+
+    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 sign(self, payload):
+        # The verification code only allows the salt length to be the
+        # same as the hash length, 32.
+        return self.key.sign(
+                data=payload,
+                padding=PSS(mgf=MGF1(SHA256()), salt_length=32),
+                algorithm=SHA256())