reEncrypt method

Future<ReEncryptResponse> reEncrypt({
  1. required Uint8List ciphertextBlob,
  2. required String destinationKeyId,
  3. EncryptionAlgorithmSpec? destinationEncryptionAlgorithm,
  4. Map<String, String>? destinationEncryptionContext,
  5. List<String>? grantTokens,
  6. EncryptionAlgorithmSpec? sourceEncryptionAlgorithm,
  7. Map<String, String>? sourceEncryptionContext,
  8. String? sourceKeyId,
})

Decrypts ciphertext and then reencrypts it entirely within AWS KMS. You can use this operation to change the customer master key (CMK) under which data is encrypted, such as when you manually rotate a CMK or change the CMK that protects a ciphertext. You can also use it to reencrypt ciphertext under the same CMK, such as to change the encryption context of a ciphertext.

The ReEncrypt operation can decrypt ciphertext that was encrypted by using an AWS KMS CMK in an AWS KMS operation, such as Encrypt or GenerateDataKey. It can also decrypt ciphertext that was encrypted by using the public key of an asymmetric CMK outside of AWS KMS. However, it cannot decrypt ciphertext produced by other libraries, such as the AWS Encryption SDK or Amazon S3 client-side encryption. These libraries return a ciphertext format that is incompatible with AWS KMS.

When you use the ReEncrypt operation, you need to provide information for the decrypt operation and the subsequent encrypt operation.

  • If your ciphertext was encrypted under an asymmetric CMK, you must use the SourceKeyId parameter to identify the CMK that encrypted the ciphertext. You must also supply the encryption algorithm that was used. This information is required to decrypt the data.
  • If your ciphertext was encrypted under a symmetric CMK, the SourceKeyId parameter is optional. AWS KMS can get this information from metadata that it adds to the symmetric ciphertext blob. This feature adds durability to your implementation by ensuring that authorized users can decrypt ciphertext decades after it was encrypted, even if they've lost track of the CMK ID. However, specifying the source CMK is always recommended as a best practice. When you use the SourceKeyId parameter to specify a CMK, AWS KMS uses only the CMK you specify. If the ciphertext was encrypted under a different CMK, the ReEncrypt operation fails. This practice ensures that you use the CMK that you intend.
  • To reencrypt the data, you must use the DestinationKeyId parameter specify the CMK that re-encrypts the data after it is decrypted. You can select a symmetric or asymmetric CMK. If the destination CMK is an asymmetric CMK, you must also provide the encryption algorithm. The algorithm that you choose must be compatible with the CMK.

The CMK that you use for this operation must be in a compatible key state. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide.

Cross-account use: Yes. The source CMK and destination CMK can be in different AWS accounts. Either or both CMKs can be in a different account than the caller.

Required permissions:

To permit reencryption from or to a CMK, include the "kms:ReEncrypt*" permission in your key policy. This permission is automatically included in the key policy when you use the console to create a CMK. But you must include it manually when you create a CMK programmatically or when you use the PutKeyPolicy operation to set a key policy.

Related operations:

May throw NotFoundException. May throw DisabledException. May throw InvalidCiphertextException. May throw KeyUnavailableException. May throw IncorrectKeyException. May throw DependencyTimeoutException. May throw InvalidKeyUsageException. May throw InvalidGrantTokenException. May throw KMSInternalException. May throw KMSInvalidStateException.

Parameter ciphertextBlob : Ciphertext of the data to reencrypt.

Parameter destinationKeyId : A unique identifier for the CMK that is used to reencrypt the data. Specify a symmetric or asymmetric CMK with a KeyUsage value of ENCRYPT_DECRYPT. To find the KeyUsage value of a CMK, use the DescribeKey operation.

To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a CMK in a different AWS account, you must use the key ARN or alias ARN.

For example:

  • Key ID: 1234abcd-12ab-34cd-56ef-1234567890ab
  • Key ARN: arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
  • Alias name: alias/ExampleAlias
  • Alias ARN: arn:aws:kms:us-east-2:111122223333:alias/ExampleAlias
To get the key ID and key ARN for a CMK, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.

Parameter destinationEncryptionAlgorithm : Specifies the encryption algorithm that AWS KMS will use to reecrypt the data after it has decrypted it. The default value, SYMMETRIC_DEFAULT, represents the encryption algorithm used for symmetric CMKs.

This parameter is required only when the destination CMK is an asymmetric CMK.

Parameter destinationEncryptionContext : Specifies that encryption context to use when the reencrypting the data.

A destination encryption context is valid only when the destination CMK is a symmetric CMK. The standard ciphertext format for asymmetric CMKs does not include fields for metadata.

An encryption context is a collection of non-secret key-value pairs that represents additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is optional when encrypting with a symmetric CMK, but it is highly recommended.

For more information, see Encryption Context in the AWS Key Management Service Developer Guide.

Parameter grantTokens : A list of grant tokens.

For more information, see Grant Tokens in the AWS Key Management Service Developer Guide.

Parameter sourceEncryptionAlgorithm : Specifies the encryption algorithm that AWS KMS will use to decrypt the ciphertext before it is reencrypted. The default value, SYMMETRIC_DEFAULT, represents the algorithm used for symmetric CMKs.

Specify the same algorithm that was used to encrypt the ciphertext. If you specify a different algorithm, the decrypt attempt fails.

This parameter is required only when the ciphertext was encrypted under an asymmetric CMK.

Parameter sourceEncryptionContext : Specifies the encryption context to use to decrypt the ciphertext. Enter the same encryption context that was used to encrypt the ciphertext.

An encryption context is a collection of non-secret key-value pairs that represents additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is optional when encrypting with a symmetric CMK, but it is highly recommended.

For more information, see Encryption Context in the AWS Key Management Service Developer Guide.

Parameter sourceKeyId : Specifies the customer master key (CMK) that AWS KMS will use to decrypt the ciphertext before it is re-encrypted. Enter a key ID of the CMK that was used to encrypt the ciphertext.

This parameter is required only when the ciphertext was encrypted under an asymmetric CMK. If you used a symmetric CMK, AWS KMS can get the CMK from metadata that it adds to the symmetric ciphertext blob. However, it is always recommended as a best practice. This practice ensures that you use the CMK that you intend.

To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a CMK in a different AWS account, you must use the key ARN or alias ARN.

For example:

  • Key ID: 1234abcd-12ab-34cd-56ef-1234567890ab
  • Key ARN: arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
  • Alias name: alias/ExampleAlias
  • Alias ARN: arn:aws:kms:us-east-2:111122223333:alias/ExampleAlias
To get the key ID and key ARN for a CMK, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.

Implementation

Future<ReEncryptResponse> reEncrypt({
  required Uint8List ciphertextBlob,
  required String destinationKeyId,
  EncryptionAlgorithmSpec? destinationEncryptionAlgorithm,
  Map<String, String>? destinationEncryptionContext,
  List<String>? grantTokens,
  EncryptionAlgorithmSpec? sourceEncryptionAlgorithm,
  Map<String, String>? sourceEncryptionContext,
  String? sourceKeyId,
}) async {
  ArgumentError.checkNotNull(ciphertextBlob, 'ciphertextBlob');
  ArgumentError.checkNotNull(destinationKeyId, 'destinationKeyId');
  _s.validateStringLength(
    'destinationKeyId',
    destinationKeyId,
    1,
    2048,
    isRequired: true,
  );
  _s.validateStringLength(
    'sourceKeyId',
    sourceKeyId,
    1,
    2048,
  );
  final headers = <String, String>{
    'Content-Type': 'application/x-amz-json-1.1',
    'X-Amz-Target': 'TrentService.ReEncrypt'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'CiphertextBlob': base64Encode(ciphertextBlob),
      'DestinationKeyId': destinationKeyId,
      if (destinationEncryptionAlgorithm != null)
        'DestinationEncryptionAlgorithm':
            destinationEncryptionAlgorithm.toValue(),
      if (destinationEncryptionContext != null)
        'DestinationEncryptionContext': destinationEncryptionContext,
      if (grantTokens != null) 'GrantTokens': grantTokens,
      if (sourceEncryptionAlgorithm != null)
        'SourceEncryptionAlgorithm': sourceEncryptionAlgorithm.toValue(),
      if (sourceEncryptionContext != null)
        'SourceEncryptionContext': sourceEncryptionContext,
      if (sourceKeyId != null) 'SourceKeyId': sourceKeyId,
    },
  );

  return ReEncryptResponse.fromJson(jsonResponse.body);
}