# 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 basic encryption and decryption of a value already in memory."""

import aws_encryption_sdk

def cycle_string(key_arn, source_plaintext, botocore_session=None):

"""Encrypts and then decrypts a string under a KMS customer master key (CMK).

:param str key_arn: Amazon Resource Name (ARN) of the KMS CMK

:param bytes source_plaintext: Data to encrypt

:param botocore_session: existing botocore session instance

:type botocore_session: botocore.session.Session

"""

# Create a KMS master key provider

kms_kwargs = dict(key_ids=[key_arn])

if botocore_session is not None:

kms_kwargs["botocore_session"] = botocore_session

master_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(**kms_kwargs)

# Encrypt the plaintext source data

ciphertext, encryptor_header = aws_encryption_sdk.encrypt(source=source_plaintext, key_provider=master_key_provider)

# Decrypt the ciphertext

cycled_plaintext, decrypted_header = aws_encryption_sdk.decrypt(source=ciphertext, key_provider=master_key_provider)

# Verify that the "cycled" (encrypted, then decrypted) plaintext is identical to the source plaintext

assert cycled_plaintext == source_plaintext

# Verify that the encryption context used in the decrypt operation includes all key pairs from

# the encrypt operation. (The SDK can add pairs, so don't require an exact match.)

#

# In production, always use a meaningful encryption context. In this sample, we omit the

# encryption context (no key pairs).

assert all(

pair in decrypted_header.encryption_context.items() for pair in encryptor_header.encryption_context.items()

)