1 files changed, 107 insertions, 0 deletions
diff --git a/tools/mcuboot/imgtool/keys/x25519.py b/tools/mcuboot/imgtool/keys/x25519.py
new file mode 100644
index 00000000..63c0b5a7
--- /dev/null
+++ b/tools/mcuboot/imgtool/keys/x25519.py
@@ -0,0 +1,107 @@
+"""
+X25519 key management
+"""
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import x25519
+
+from .general import KeyClass
+
+
+class X25519UsageError(Exception):
+    pass
+
+
+class X25519Public(KeyClass):
+    def __init__(self, key):
+        self.key = key
+
+    def shortname(self):
+        return "x25519"
+
+    def _unsupported(self, name):
+        raise X25519UsageError("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 "X25519"
+
+    def sig_tlv(self):
+        return "X25519"
+
+    def sig_len(self):
+        return 32
+
+
+class X25519(X25519Public):
+    """
+    Wrapper around an X25519 private key.
+    """
+
+    def __init__(self, key):
+        """key should be an instance of EllipticCurvePrivateKey"""
+        self.key = key
+
+    @staticmethod
+    def generate():
+        pk = x25519.X25519PrivateKey.generate()
+        return X25519(pk)
+
+    def _get_public(self):
+        return self.key.public_key()
+
+    def get_private_bytes(self, minimal):
+        return self.key.private_bytes(
+            encoding=serialization.Encoding.DER,
+            format=serialization.PrivateFormat.PKCS8,
+            encryption_algorithm=serialization.NoEncryption())
+
+    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_digest(self, digest):
+        """Return the actual signature"""
+        return self.key.sign(data=digest)
+
+    def verify_digest(self, signature, digest):
+        """Verify that signature is valid for given digest"""
+        k = self.key
+        if isinstance(self.key, x25519.X25519PrivateKey):
+            k = self.key.public_key()
+        return k.verify(signature=signature, data=digest)