Merge pull request #3 from ARMmbed/feature/convert-ecdsa-pubkey

Add a public key conversion function

ec_key_to_mbedtls_points.py

@@ -0,0 +1,52 @@
+#!/usr/bin/python3
+# -*- coding: utf-8 -*-
+# ----------------------------------------------------------------------------
+# Copyright 2018 ARM Limited or its affiliates
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ----------------------------------------------------------------------------
+'''
+Converts a ECDSA PEM public key to the format needed by libcose + mbedtls
+
+Invoke with: 'ec_key_to_mbedtls_points.py pubkey.pem'
+'''
+import sys
+import binascii
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives.serialization import load_pem_public_key
+
+MBEDTLS_ECP_MAX_BYTES = 66
+HEX_VALUES_PER_LINE = 12
+
+keystr = None
+with open(sys.argv[1], 'rb') as fd:
+    keystr = fd.read()
+
+key = load_pem_public_key(keystr, backend=default_backend())
+
+xa = ['0x%02x'% x for x in binascii.a2b_hex(('%%0%dx'%(2*MBEDTLS_ECP_MAX_BYTES))%key.public_numbers().x)]
+ya = ['0x%02x'% x for x in binascii.a2b_hex(('%%0%dx'%(2*MBEDTLS_ECP_MAX_BYTES))%key.public_numbers().y)]
+
+print('const unsigned char mbedtls_ec_public_key_x [MBEDTLS_ECP_MAX_BYTES] = {')
+while xa:
+    print('    ' + ', '.join(xa[:HEX_VALUES_PER_LINE]) + ',')
+    xa = xa[HEX_VALUES_PER_LINE:]
+print('};')
+
+print('const unsigned char mbedtls_ec_public_key_y [MBEDTLS_ECP_MAX_BYTES] = {')
+while ya:
+    print('    ' + ', '.join(ya[:HEX_VALUES_PER_LINE]) + ',')
+    ya = ya[HEX_VALUES_PER_LINE:]
+print('};')