verify method

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

Verifies a digital signature that was generated by the Sign operation.

Verification confirms that an authorized user signed the message with the specified CMK and signing algorithm, and the message hasn't changed since it was signed. If the signature is verified, the value of the SignatureValid field in the response is True. If the signature verification fails, the Verify operation fails with an KMSInvalidSignatureException exception.

A digital signature is generated by using the private key in an asymmetric CMK. The signature is verified by using the public key in the same asymmetric CMK. For information about symmetric and asymmetric CMKs, see Using Symmetric and Asymmetric CMKs in the AWS Key Management Service Developer Guide.

To verify a digital signature, you can use the Verify operation. Specify the same asymmetric CMK, message, and signing algorithm that were used to produce the signature.

You can also verify the digital signature by using the public key of the CMK outside of AWS KMS. Use the GetPublicKey operation to download the public key in the asymmetric CMK and then use the public key to verify the signature outside of AWS KMS. The advantage of using the Verify operation is that it is performed within AWS KMS. As a result, it's easy to call, the operation is performed within the FIPS boundary, it is logged in AWS CloudTrail, and you can use key policy and IAM policy to determine who is authorized to use the CMK to verify signatures.

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:Verify (key policy)

Related operations: Sign

May throw NotFoundException. May throw DisabledException. May throw KeyUnavailableException. May throw DependencyTimeoutException. May throw InvalidKeyUsageException. May throw InvalidGrantTokenException. May throw KMSInternalException. May throw KMSInvalidStateException. May throw KMSInvalidSignatureException.

Parameter keyId : Identifies the asymmetric CMK that will be used to verify the signature. This must be the same CMK that was used to generate the signature. If you specify a different CMK, the signature verification fails.

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 that was signed. You can submit a raw message of up to 4096 bytes, or a hash digest of the message. If you submit a digest, use the MessageType parameter with a value of DIGEST.

If the message specified here is different from the message that was signed, the signature verification fails. A message and its hash digest are considered to be the same message.

Parameter signature : The signature that the Sign operation generated.

Parameter signingAlgorithm : The signing algorithm that was used to sign the message. If you submit a different algorithm, the signature verification fails.

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<VerifyResponse> verify({
  required String keyId,
  required Uint8List message,
  required Uint8List signature,
  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(signature, 'signature');
  ArgumentError.checkNotNull(signingAlgorithm, 'signingAlgorithm');
  final headers = <String, String>{
    'Content-Type': 'application/x-amz-json-1.1',
    'X-Amz-Target': 'TrentService.Verify'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'KeyId': keyId,
      'Message': base64Encode(message),
      'Signature': base64Encode(signature),
      'SigningAlgorithm': signingAlgorithm.toValue(),
      if (grantTokens != null) 'GrantTokens': grantTokens,
      if (messageType != null) 'MessageType': messageType.toValue(),
    },
  );

  return VerifyResponse.fromJson(jsonResponse.body);
}