AWS SDK Version 3 for .NET
API Reference

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Generates a hash-based message authentication code (HMAC) for a message using an HMAC KMS key and a MAC algorithm that the key supports. HMAC KMS keys and the HMAC algorithms that KMS uses conform to industry standards defined in RFC 2104.

You can use value that GenerateMac returns in the VerifyMac operation to demonstrate that the original message has not changed. Also, because a secret key is used to create the hash, you can verify that the party that generated the hash has the required secret key. You can also use the raw result to implement HMAC-based algorithms such as key derivation functions. 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.

Best practices recommend that you limit the time during which any signing mechanism, including an HMAC, is effective. This deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded. HMAC tags do not include a timestamp, but you can include a timestamp in the token or message to help you detect when its time to refresh the HMAC.

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:GenerateMac (key policy)

Related operations: VerifyMac


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

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


public virtual GenerateMacResponse GenerateMac(
         GenerateMacRequest request
Type: Amazon.KeyManagementService.Model.GenerateMacRequest

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

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


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.
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.


This example generates an HMAC for a message, an HMAC KMS key, and a MAC algorithm. The algorithm must be supported by the specified HMAC KMS key.

To generate an HMAC for a message

var client = new AmazonKeyManagementServiceClient();
var response = client.GenerateMac(new GenerateMacRequest 
    KeyId = "1234abcd-12ab-34cd-56ef-1234567890ab", // The HMAC KMS key input to the HMAC algorithm.
    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 KMS key used in the operation.
MemoryStream mac = response.Mac; // The HMAC tag that results from this operation.
string macAlgorithm = response.MacAlgorithm; // The HMAC algorithm used in the operation.


Version Information

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

See Also