basic_file_encryption_with_raw_key_provider.py

# Copyright 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file 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.
"""Example showing creation and use of a RawMasterKeyProvider."""
import filecmp
import os

import aws_encryption_sdk
from aws_encryption_sdk.identifiers import Algorithm, CommitmentPolicy, EncryptionKeyType, WrappingAlgorithm
from aws_encryption_sdk.internal.crypto.wrapping_keys import WrappingKey
from aws_encryption_sdk.key_providers.raw import RawMasterKeyProvider


class StaticRandomMasterKeyProvider(RawMasterKeyProvider):
    """Randomly generates 256-bit keys for each unique key ID."""

    provider_id = "static-random"

    def __init__(self, **kwargs):  # pylint: disable=unused-argument
        """Initialize empty map of keys."""
        self._static_keys = {}

    def _get_raw_key(self, key_id):
        """Returns a static, randomly-generated symmetric key for the specified key ID.

        :param str key_id: Key ID
        :returns: Wrapping key that contains the specified static key
        :rtype: :class:`aws_encryption_sdk.internal.crypto.WrappingKey`
        """
        try:
            static_key = self._static_keys[key_id]
        except KeyError:
            static_key = os.urandom(32)
            self._static_keys[key_id] = static_key
        return WrappingKey(
            wrapping_algorithm=WrappingAlgorithm.AES_256_GCM_IV12_TAG16_NO_PADDING,
            wrapping_key=static_key,
            wrapping_key_type=EncryptionKeyType.SYMMETRIC,
        )


def cycle_file(source_plaintext_filename):
    """Encrypts and then decrypts a file under a custom static master key provider.

    :param str source_plaintext_filename: Filename of file to encrypt
    """
    # Set up an encryption client with an explicit commitment policy. Note that if you do not explicitly choose a
    # commitment policy, REQUIRE_ENCRYPT_REQUIRE_DECRYPT is used by default.
    client = aws_encryption_sdk.EncryptionSDKClient(commitment_policy=CommitmentPolicy.REQUIRE_ENCRYPT_REQUIRE_DECRYPT)

    # Create a static random master key provider
    key_id = os.urandom(8)
    master_key_provider = StaticRandomMasterKeyProvider()
    master_key_provider.add_master_key(key_id)

    ciphertext_filename = source_plaintext_filename + ".encrypted"
    cycled_plaintext_filename = source_plaintext_filename + ".decrypted"

    # Encrypt the plaintext source data
    # We can use an unsigning algorithm suite here under the assumption that the contexts that encrypt
    # and decrypt are equally trusted.
    with open(source_plaintext_filename, "rb") as plaintext, open(ciphertext_filename, "wb") as ciphertext:
        with client.stream(
            algorithm=Algorithm.AES_256_GCM_HKDF_SHA512_COMMIT_KEY,
            mode="e",
            source=plaintext,
            key_provider=master_key_provider,
        ) as encryptor:
            for chunk in encryptor:
                ciphertext.write(chunk)

    # Decrypt the ciphertext
    # We can use the recommended "decrypt-unsigned" streaming mode since we encrypted with an unsigned algorithm suite.
    with open(ciphertext_filename, "rb") as ciphertext, open(cycled_plaintext_filename, "wb") as plaintext:
        with client.stream(mode="decrypt-unsigned", source=ciphertext, key_provider=master_key_provider) as decryptor:
            for chunk in decryptor:
                plaintext.write(chunk)

    # Verify that the "cycled" (encrypted, then decrypted) plaintext is identical to the source
    # plaintext
    assert filecmp.cmp(source_plaintext_filename, cycled_plaintext_filename)

    # Verify that the encryption context used in the decrypt operation includes all key pairs from
    # the encrypt operation
    #
    # In production, always use a meaningful encryption context. In this sample, we omit the
    # encryption context (no key pairs).
    assert all(
        pair in decryptor.header.encryption_context.items() for pair in encryptor.header.encryption_context.items()
    )
    return ciphertext_filename, cycled_plaintext_filename