AWS SDK Version 3 for .NET
API Reference

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Verifies the hash-based message authentication code (HMAC) for a specified message, HMAC KMS key, and MAC algorithm. To verify the HMAC, VerifyMac computes an HMAC using the message, HMAC KMS key, and MAC algorithm that you specify, and compares the computed HMAC to the HMAC that you specify. If the HMACs are identical, the verification succeeds; otherwise, it fails. Verification indicates that the message hasn't changed since the HMAC was calculated, and the specified key was used to generate and verify the HMAC.

HMAC KMS keys and the HMAC algorithms that KMS uses conform to industry standards defined in RFC 2104.

This operation is part of KMS support for HMAC KMS keys. For details, see HMAC keys in KMS in the Key Management Service Developer Guide.

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:VerifyMac (key policy)

Related operations: GenerateMac

Note:

For .NET Core this operation is only available in asynchronous form. Please refer to VerifyMacAsync.

Namespace: Amazon.KeyManagementService
Assembly: AWSSDK.KeyManagementService.dll
Version: 3.x.y.z

Syntax

C#
public virtual VerifyMacResponse VerifyMac(
         VerifyMacRequest request
)
Parameters
request
Type: Amazon.KeyManagementService.Model.VerifyMacRequest

Container for the necessary parameters to execute the VerifyMac service method.

Return Value
The response from the VerifyMac service method, as returned by KeyManagementService.

Exceptions

ExceptionCondition
DisabledException The request was rejected because the specified KMS key is not enabled.
InvalidGrantTokenException The request was rejected because the specified grant token is not valid.
InvalidKeyUsageException The request was rejected for one of the following reasons: The KeyUsage value of the KMS key is incompatible with the API operation. The encryption algorithm or signing algorithm specified for the operation is incompatible with the type of key material in the KMS key (KeySpec). For encrypting, decrypting, re-encrypting, and generating data keys, the KeyUsage must be ENCRYPT_DECRYPT. For signing and verifying messages, the KeyUsage must be SIGN_VERIFY. For generating and verifying message authentication codes (MACs), the KeyUsage must be GENERATE_VERIFY_MAC. To find the KeyUsage of a KMS key, use the DescribeKey operation. To find the encryption or signing algorithms supported for a particular KMS key, use the DescribeKey operation.
KeyUnavailableException The request was rejected because the specified KMS key was not available. You can retry the request.
KMSInternalException The request was rejected because an internal exception occurred. The request can be retried.
KMSInvalidMacException The request was rejected because the HMAC verification failed. HMAC verification fails when the HMAC computed by using the specified message, HMAC KMS key, and MAC algorithm does not match the HMAC specified in the request.
KMSInvalidStateException The request was rejected because the state of the specified resource is not valid for this request. This exceptions means one of the following: The key state of the KMS key is not compatible with the operation. To find the key state, use the DescribeKey operation. For more information about which key states are compatible with each KMS operation, see Key states of KMS keys in the Key Management Service Developer Guide. For cryptographic operations on KMS keys in custom key stores, this exception represents a general failure with many possible causes. To identify the cause, see the error message that accompanies the exception.
NotFoundException The request was rejected because the specified entity or resource could not be found.

Examples

This example verifies an HMAC for a particular message, HMAC KMS keys, and MAC algorithm. A value of 'true' in the MacValid value in the response indicates that the HMAC is valid.

To verify an HMAC


var client = new AmazonKeyManagementServiceClient();
var response = client.VerifyMac(new VerifyMacRequest 
{
    KeyId = "1234abcd-12ab-34cd-56ef-1234567890ab", // The HMAC KMS key input to the HMAC algorithm.
    Mac = new MemoryStream(<HMAC_TAG>), // The HMAC to be verified.
    MacAlgorithm = "HMAC_SHA_384", // The HMAC algorithm requested for the operation.
    Message = new MemoryStream(Hello World) // The message input to the HMAC algorithm.
});

string keyId = response.KeyId; // The key ARN of the HMAC key used in the operation.
string macAlgorithm = response.MacAlgorithm; // The HMAC algorithm used in the operation.
bool macValid = response.MacValid; // A value of 'true' indicates that verification succeeded. If verification fails, the call to VerifyMac fails.

            

Version Information

.NET Framework:
Supported in: 4.5, 4.0, 3.5

See Also