verify method

Future<VerifyResponse> verify({
  1. required String keyId,
  2. required Uint8List message,
  3. required Uint8List signature,
  4. required SigningAlgorithmSpec signingAlgorithm,
  5. bool? dryRun,
  6. List<String>? grantTokens,
  7. 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 KMS key 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 KMS key. The signature is verified by using the public key in the same asymmetric KMS key. For information about asymmetric KMS keys, see Asymmetric KMS keys in the Key Management Service Developer Guide.

To use the Verify operation, specify the same asymmetric KMS key, message, and signing algorithm that were used to produce the signature. The message type does not need to be the same as the one used for signing, but it must indicate whether the value of the Message parameter should be hashed as part of the verification process.

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

To verify a signature outside of KMS with an SM2 public key (China Regions only), you must specify the distinguishing ID. By default, KMS uses 1234567812345678 as the distinguishing ID. For more information, see Offline verification with SM2 key pairs.

The KMS key that you use for this operation must be in a compatible key state. For details, see Key states of KMS keys in the Key Management Service Developer Guide.

Cross-account use: Yes. To perform this operation with a KMS key in a different Amazon Web Services account, specify the key ARN or alias ARN in the value of the KeyId parameter.

Required permissions: kms:Verify (key policy)

Related operations: Sign

Eventual consistency: The KMS API follows an eventual consistency model. For more information, see KMS eventual consistency.

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

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

To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a KMS key in a different Amazon Web Services 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 KMS key, 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 dryRun : Checks if your request will succeed. DryRun is an optional parameter.

To learn more about how to use this parameter, see Testing your permissions in the Key Management Service Developer Guide.

Parameter grantTokens : A list of grant tokens.

Use a grant token when your permission to call this operation comes from a new grant that has not yet achieved eventual consistency. For more information, see Grant token and Using a grant token in the Key Management Service Developer Guide.

Parameter messageType : Tells KMS whether the value of the Message parameter should be hashed as part of the signing algorithm. Use RAW for unhashed messages; use DIGEST for message digests, which are already hashed; use EXTERNAL_MU for 64-byte representative μ used in ML-DSA signing as defined in NIST FIPS 204 Section 6.2.

When the value of MessageType is RAW, KMS uses the standard signing algorithm, which begins with a hash function. When the value is DIGEST, KMS skips the hashing step in the signing algorithm. When the value is EXTERNAL_MU KMS skips the concatenated hashing of the public key hash and the message done in the ML-DSA signing algorithm. When using ECC_NIST_EDWARDS25519 KMS keys:

  • ED25519_SHA_512 signing algorithm requires KMS MessageType:RAW
  • ED25519_PH_SHA_512 signing algorithm requires KMS MessageType:DIGEST
When the value of MessageType is DIGEST, the length of the Message value must match the length of hashed messages for the specified signing algorithm.

When the value of MessageType is EXTERNAL_MU the length of the Message value must be 64 bytes.

You can submit a message digest and omit the MessageType or specify RAW so the digest is hashed again while signing. However, if the signed message is hashed once while signing, but twice while verifying, verification fails, even when the message hasn't changed.

The hashing algorithm that Verify uses is based on the SigningAlgorithm value.

  • Signing algorithms that end in SHA_256 use the SHA_256 hashing algorithm.
  • Signing algorithms that end in SHA_384 use the SHA_384 hashing algorithm.
  • Signing algorithms that end in SHA_512 use the SHA_512 hashing algorithm.
  • Signing algorithms that end in SHAKE_256 use the SHAKE_256 hashing algorithm.
  • SM2DSA uses the SM3 hashing algorithm. For details, see Offline verification with SM2 key pairs.

Implementation

Future<VerifyResponse> verify({
  required String keyId,
  required Uint8List message,
  required Uint8List signature,
  required SigningAlgorithmSpec signingAlgorithm,
  bool? dryRun,
  List<String>? grantTokens,
  MessageType? messageType,
}) async {
  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.value,
      if (dryRun != null) 'DryRun': dryRun,
      if (grantTokens != null) 'GrantTokens': grantTokens,
      if (messageType != null) 'MessageType': messageType.value,
    },
  );

  return VerifyResponse.fromJson(jsonResponse.body);
}