generateDataKeyWithoutPlaintext method
Generates a unique symmetric data key. This operation returns a data key that is encrypted under a customer master key (CMK) that you specify. To request an asymmetric data key pair, use the GenerateDataKeyPair or GenerateDataKeyPairWithoutPlaintext operations.
GenerateDataKeyWithoutPlaintext is identical to the
GenerateDataKey operation except that returns only the encrypted
copy of the data key. This operation is useful for systems that need to
encrypt data at some point, but not immediately. When you need to encrypt
the data, you call the Decrypt operation on the encrypted copy of
the key.
It's also useful in distributed systems with different levels of trust. For example, you might store encrypted data in containers. One component of your system creates new containers and stores an encrypted data key with each container. Then, a different component puts the data into the containers. That component first decrypts the data key, uses the plaintext data key to encrypt data, puts the encrypted data into the container, and then destroys the plaintext data key. In this system, the component that creates the containers never sees the plaintext data key.
GenerateDataKeyWithoutPlaintext returns a unique data key for
each request. The bytes in the keys are not related to the caller or CMK
that is used to encrypt the private key.
To generate a data key, you must specify the symmetric customer master key (CMK) that is used to encrypt the data key. You cannot use an asymmetric CMK to generate a data key. To get the type of your CMK, use the DescribeKey operation.
If the operation succeeds, you will find the encrypted copy of the data
key in the CiphertextBlob field.
You can use the optional encryption context to add additional security to
the encryption operation. If you specify an
EncryptionContext, you must specify the same encryption
context (a case-sensitive exact match) when decrypting the encrypted data
key. Otherwise, the request to decrypt fails with an
InvalidCiphertextException. For more information, see Encryption
Context in the AWS Key Management Service Developer Guide.
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. To perform this operation with a CMK in a
different AWS account, specify the key ARN or alias ARN in the value of
the KeyId parameter.
Required permissions: kms:GenerateDataKeyWithoutPlaintext (key policy)
Related operations:
May throw NotFoundException. May throw DisabledException. May throw KeyUnavailableException. May throw DependencyTimeoutException. May throw InvalidKeyUsageException. May throw InvalidGrantTokenException. May throw KMSInternalException. May throw KMSInvalidStateException.
Parameter keyId :
The identifier of the symmetric customer master key (CMK) that encrypts
the data key.
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
Parameter encryptionContext :
Specifies the encryption context that will be used when encrypting the
data key.
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 keySpec :
The length of the data key. Use AES_128 to generate a 128-bit
symmetric key, or AES_256 to generate a 256-bit symmetric
key.
Parameter numberOfBytes :
The length of the data key in bytes. For example, use the value 64 to
generate a 512-bit data key (64 bytes is 512 bits). For common key lengths
(128-bit and 256-bit symmetric keys), we recommend that you use the
KeySpec field instead of this one.
Implementation
Future<GenerateDataKeyWithoutPlaintextResponse>
generateDataKeyWithoutPlaintext({
required String keyId,
Map<String, String>? encryptionContext,
List<String>? grantTokens,
DataKeySpec? keySpec,
int? numberOfBytes,
}) async {
ArgumentError.checkNotNull(keyId, 'keyId');
_s.validateStringLength(
'keyId',
keyId,
1,
2048,
isRequired: true,
);
_s.validateNumRange(
'numberOfBytes',
numberOfBytes,
1,
1024,
);
final headers = <String, String>{
'Content-Type': 'application/x-amz-json-1.1',
'X-Amz-Target': 'TrentService.GenerateDataKeyWithoutPlaintext'
};
final jsonResponse = await _protocol.send(
method: 'POST',
requestUri: '/',
exceptionFnMap: _exceptionFns,
// TODO queryParams
headers: headers,
payload: {
'KeyId': keyId,
if (encryptionContext != null) 'EncryptionContext': encryptionContext,
if (grantTokens != null) 'GrantTokens': grantTokens,
if (keySpec != null) 'KeySpec': keySpec.toValue(),
if (numberOfBytes != null) 'NumberOfBytes': numberOfBytes,
},
);
return GenerateDataKeyWithoutPlaintextResponse.fromJson(jsonResponse.body);
}