sign method

Future<SignResponse> sign({ required String keyId, required Uint8List message, required SigningAlgorithmSpec signingAlgorithm, List<String>? grantTokens, MessageType? messageType, })

Creates a digital signature for a message or message digest by using the private key in an asymmetric CMK. To verify the signature, use the Verify operation, or use the public key in the same asymmetric CMK outside of AWS KMS. For information about symmetric and asymmetric CMKs, see Using Symmetric and Asymmetric CMKs in the AWS Key Management Service Developer Guide.

Digital signatures are generated and verified by using asymmetric key pair, such as an RSA or ECC pair that is represented by an asymmetric customer master key (CMK). The key owner (or an authorized user) uses their private key to sign a message. Anyone with the public key can verify that the message was signed with that particular private key and that the message hasn't changed since it was signed.

To use the Sign operation, provide the following information:

• Use the KeyId parameter to identify an asymmetric CMK with a KeyUsage value of SIGN_VERIFY. To get the KeyUsage value of a CMK, use the DescribeKey operation. The caller must have kms:Sign permission on the CMK.
• Use the Message parameter to specify the message or message digest to sign. You can submit messages of up to 4096 bytes. To sign a larger message, generate a hash digest of the message, and then provide the hash digest in the Message parameter. To indicate whether the message is a full message or a digest, use the MessageType parameter.
• Choose a signing algorithm that is compatible with the CMK.

To verify the signature that this operation generates, use the Verify operation. Or use the GetPublicKey operation to download the public key and then use the public key to verify the signature outside of AWS KMS.

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:Sign (key policy)

Related operations: Verify

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 : Identifies an asymmetric CMK. AWS KMS uses the private key in the asymmetric CMK to sign the message. The KeyUsage type of the CMK must be SIGN_VERIFY. To find the KeyUsage 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 message : Specifies the message or message digest to sign. Messages can be 0-4096 bytes. To sign a larger message, provide the message digest.

If you provide a message, AWS KMS generates a hash digest of the message and then signs it.

Parameter signingAlgorithm : Specifies the signing algorithm to use when signing the message.

Choose an algorithm that is compatible with the type and size of the specified asymmetric CMK.

Parameter grantTokens : A list of grant tokens.

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

Parameter messageType : Tells AWS KMS whether the value of the Message parameter is a message or message digest. The default value, RAW, indicates a message. To indicate a message digest, enter DIGEST.

Implementation

Future<SignResponse> sign({
  required String keyId,
  required Uint8List message,
  required SigningAlgorithmSpec signingAlgorithm,
  List<String>? grantTokens,
  MessageType? messageType,
}) async {
  ArgumentError.checkNotNull(keyId, 'keyId');
  _s.validateStringLength(
    'keyId',
    keyId,
    1,
    2048,
    isRequired: true,
  );
  ArgumentError.checkNotNull(message, 'message');
  ArgumentError.checkNotNull(signingAlgorithm, 'signingAlgorithm');
  final headers = <String, String>{
    'Content-Type': 'application/x-amz-json-1.1',
    'X-Amz-Target': 'TrentService.Sign'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'KeyId': keyId,
      'Message': base64Encode(message),
      'SigningAlgorithm': signingAlgorithm.toValue(),
      if (grantTokens != null) 'GrantTokens': grantTokens,
      if (messageType != null) 'MessageType': messageType.toValue(),
    },
  );

  return SignResponse.fromJson(jsonResponse.body);
}