text: # Original code taken from mcuboot project at:
  # https://github.com/mcu-tools/mcuboot
  # Git SHA of the original version: a8e12dae381080e898cea0c6f7408009b0163f9f
  #
  # 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.
  """
  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
  