1 files changed, 157 insertions, 0 deletions
diff --git a/tools/mcuboot/imgtool/keys/ecdsa.py b/tools/mcuboot/imgtool/keys/ecdsa.py
new file mode 100644
index 00000000..139d583d
--- /dev/null
+++ b/tools/mcuboot/imgtool/keys/ecdsa.py
@@ -0,0 +1,157 @@
+"""
+ECDSA key management
+"""
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives.hashes import SHA256
+
+from .general import KeyClass
+
+class ECDSAUsageError(Exception):
+    pass
+
+class ECDSA256P1Public(KeyClass):
+    def __init__(self, key):
+        self.key = key
+
+    def shortname(self):
+        return "ecdsa"
+
+    def _unsupported(self, name):
+        raise ECDSAUsageError("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 "ECDSA256_SHA256"
+
+    def sig_tlv(self):
+        return "ECDSA256"
+
+    def sig_len(self):
+        # Early versions of MCUboot (< v1.5.0) required ECDSA
+        # signatures to be padded to 72 bytes.  Because the DER
+        # encoding is done with signed integers, the size of the
+        # signature will vary depending on whether the high bit is set
+        # in each value.  This padding was done in a
+        # not-easily-reversible way (by just adding zeros).
+        #
+        # The signing code no longer requires this padding, and newer
+        # versions of MCUboot don't require it.  But, continue to
+        # return the total length so that the padding can be done if
+        # requested.
+        return 72
+
+    def verify(self, signature, payload):
+        # strip possible paddings added during sign
+        signature = signature[:signature[1] + 2]
+        k = self.key
+        if isinstance(self.key, ec.EllipticCurvePrivateKey):
+            k = self.key.public_key()
+        return k.verify(signature=signature, data=payload,
+                        signature_algorithm=ec.ECDSA(SHA256()))
+
+
+class ECDSA256P1(ECDSA256P1Public):
+    """
+    Wrapper around an ECDSA private key.
+    """
+
+    def __init__(self, key):
+        """key should be an instance of EllipticCurvePrivateKey"""
+        self.key = key
+        self.pad_sig = False
+
+    @staticmethod
+    def generate():
+        pk = ec.generate_private_key(
+            ec.SECP256R1(),
+            backend=default_backend())
+        return ECDSA256P1(pk)
+
+    def _get_public(self):
+        return self.key.public_key()
+
+    def _build_minimal_ecdsa_privkey(self, der):
+        '''
+        Builds a new DER that only includes the EC private key, removing the
+        public key that is added as an "optional" BITSTRING.
+        '''
+        offset_PUB = 68
+        EXCEPTION_TEXT = "Error parsing ecdsa key. Please submit an issue!"
+        if der[offset_PUB] != 0xa1:
+            raise ECDSAUsageError(EXCEPTION_TEXT)
+        len_PUB = der[offset_PUB + 1]
+        b = bytearray(der[:-offset_PUB])
+        offset_SEQ = 29
+        if b[offset_SEQ] != 0x30:
+            raise ECDSAUsageError(EXCEPTION_TEXT)
+        b[offset_SEQ + 1] -= len_PUB
+        offset_OCT_STR = 27
+        if b[offset_OCT_STR] != 0x04:
+            raise ECDSAUsageError(EXCEPTION_TEXT)
+        b[offset_OCT_STR + 1] -= len_PUB
+        if b[0] != 0x30 or b[1] != 0x81:
+            raise ECDSAUsageError(EXCEPTION_TEXT)
+        b[2] -= len_PUB
+        return b
+
+    def get_private_bytes(self, minimal):
+        priv = self.key.private_bytes(
+            encoding=serialization.Encoding.DER,
+            format=serialization.PrivateFormat.PKCS8,
+            encryption_algorithm=serialization.NoEncryption())
+        if minimal:
+            priv = self._build_minimal_ecdsa_privkey(priv)
+        return priv
+
+    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 raw_sign(self, payload):
+        """Return the actual signature"""
+        return self.key.sign(
+            data=payload,
+            signature_algorithm=ec.ECDSA(SHA256()))
+
+    def sign(self, payload):
+        sig = self.raw_sign(payload)
+        if self.pad_sig:
+            # To make fixed length, pad with one or two zeros.
+            sig += b'\000' * (self.sig_len() - len(sig))
+            return sig
+        else:
+            return sig