AWS SDK Version 3 for .NET
API Reference

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Container for the parameters to the GenerateMac operation. 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deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded.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

Inheritance Hierarchy


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


public class GenerateMacRequest : AmazonKeyManagementServiceRequest

The GenerateMacRequest type exposes the following members


Public Method GenerateMacRequest()


Public Property GrantTokens System.Collections.Generic.List<System.String>

Gets and sets the property 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.

Public Property KeyId System.String

Gets and sets the property KeyId.

The HMAC KMS key to use in the operation. The MAC algorithm computes the HMAC for the message and the key as described in RFC 2104.

To identify an HMAC KMS key, use the DescribeKey operation and see the KeySpec field in the response.

Public Property MacAlgorithm Amazon.KeyManagementService.MacAlgorithmSpec

Gets and sets the property MacAlgorithm.

The MAC algorithm used in the operation.

The algorithm must be compatible with the HMAC KMS key that you specify. To find the MAC algorithms that your HMAC KMS key supports, use the DescribeKey operation and see the MacAlgorithms field in the DescribeKey response.

Public Property Message System.IO.MemoryStream

Gets and sets the property Message.

The message to be hashed. Specify a message of up to 4,096 bytes.

GenerateMac and VerifyMac do not provide special handling for message digests. If you generate an HMAC for a hash digest of a message, you must verify the HMAC of the same hash digest.


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 Core App:
Supported in: 3.1

.NET Standard:
Supported in: 2.0

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