<a id="cli-aws-kms-generate-mac"></a>

# generate-mac

## Description

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](https://datatracker.ietf.org/doc/html/rfc2104) .

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](https://docs.aws.amazon.com/kms/latest/developerguide/hmac.html) in the \* *Key Management Service Developer Guide* \* .

#### NOTE
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deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded.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](https://docs.aws.amazon.com/kms/latest/developerguide/key-state.html) 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](https://docs.aws.amazon.com/kms/latest/developerguide/kms-api-permissions-reference.html) (key policy)

> **Related operations** :  VerifyMac

> **Eventual consistency** : The KMS API follows an eventual consistency model. For more information, see [KMS eventual consistency](https://docs.aws.amazon.com/kms/latest/developerguide/accessing-kms.html#programming-eventual-consistency) .

See also: [AWS API Documentation](https://docs.aws.amazon.com/goto/WebAPI/kms-2014-11-01/GenerateMac)

## Synopsis

```
  generate-mac
--message <value>
--key-id <value>
--mac-algorithm <value>
[--grant-tokens <value>]
[--dry-run | --no-dry-run]
[--cli-input-json | --cli-input-yaml]
[--generate-cli-skeleton <value>]
[--debug]
[--endpoint-url <value>]
[--no-verify-ssl]
[--no-paginate]
[--output <value>]
[--query <value>]
[--profile <value>]
[--region <value>]
[--version <value>]
[--color <value>]
[--no-sign-request]
[--ca-bundle <value>]
[--cli-read-timeout <value>]
[--cli-connect-timeout <value>]
[--cli-binary-format <value>]
[--no-cli-pager]
[--cli-auto-prompt]
[--no-cli-auto-prompt]
[--cli-error-format <value>]
```

## Options

`--message` (blob) [required]

> 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.

> Constraints:

> * min: `1`
> * max: `4096`

`--key-id` (string) [required]

> 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](https://datatracker.ietf.org/doc/html/rfc2104) .

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

> Constraints:

> * min: `1`
> * max: `2048`

`--mac-algorithm` (string) [required]

> 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.

> Possible values:

> * `HMAC_SHA_224`
> * `HMAC_SHA_256`
> * `HMAC_SHA_384`
> * `HMAC_SHA_512`

`--grant-tokens` (list)

> 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](https://docs.aws.amazon.com/kms/latest/developerguide/grants.html#grant_token) and [Using a grant token](https://docs.aws.amazon.com/kms/latest/developerguide/using-grant-token.html) in the *Key Management Service Developer Guide* .

> Constraints:

> * min: `0`
> * max: `10`

> (string)

> > Constraints:

> > * min: `1`
> > * max: `8192`

Syntax:

```
"string" "string" ...
```

`--dry-run` | `--no-dry-run` (boolean)

> Checks if your request will succeed. `DryRun` is an optional parameter.

> To learn more about how to use this parameter, see [Testing your permissions](https://docs.aws.amazon.com/kms/latest/developerguide/testing-permissions.html) in the *Key Management Service Developer Guide* .

`--cli-input-json` | `--cli-input-yaml` (string)
Reads arguments from the JSON string provided. The JSON string follows the format provided by `--generate-cli-skeleton`. If other arguments are provided on the command line, those values will override the JSON-provided values. It is not possible to pass arbitrary binary values using a JSON-provided value as the string will be taken literally. This may not be specified along with `--cli-input-yaml`.

`--generate-cli-skeleton` (string)
Prints a JSON skeleton to standard output without sending an API request. If provided with no value or the value `input`, prints a sample input JSON that can be used as an argument for `--cli-input-json`. Similarly, if provided `yaml-input` it will print a sample input YAML that can be used with `--cli-input-yaml`. If provided with the value `output`, it validates the command inputs and returns a sample output JSON for that command. The generated JSON skeleton is not stable between versions of the AWS CLI and there are no backwards compatibility guarantees in the JSON skeleton generated.

## Global Options

`--debug` (boolean)

Turn on debug logging.

`--endpoint-url` (string)

Override command’s default URL with the given URL.

`--no-verify-ssl` (boolean)

By default, the AWS CLI uses SSL when communicating with AWS services. For each SSL connection, the AWS CLI will verify SSL certificates. This option overrides the default behavior of verifying SSL certificates.

`--no-paginate` (boolean)

Disable automatic pagination. If automatic pagination is disabled, the AWS CLI will only make one call, for the first page of results.

`--output` (string)

The formatting style for command output.

* json
* text
* table
* yaml
* yaml-stream
* off

`--query` (string)

A JMESPath query to use in filtering the response data.

`--profile` (string)

Use a specific profile from your credential file.

`--region` (string)

The region to use. Overrides config/env settings.

`--version` (string)

Display the version of this tool.

`--color` (string)

Turn on/off color output.

* on
* off
* auto

`--no-sign-request` (boolean)

Do not sign requests. Credentials will not be loaded if this argument is provided.

`--ca-bundle` (string)

The CA certificate bundle to use when verifying SSL certificates. Overrides config/env settings.

`--cli-read-timeout` (int)

The maximum socket read time in seconds. If the value is set to 0, the socket read will be blocking and not timeout. The default value is 60 seconds.

`--cli-connect-timeout` (int)

The maximum socket connect time in seconds. If the value is set to 0, the socket connect will be blocking and not timeout. The default value is 60 seconds.

`--cli-binary-format` (string)

The formatting style to be used for binary blobs. The default format is base64. The base64 format expects binary blobs to be provided as a base64 encoded string. The raw-in-base64-out format preserves compatibility with AWS CLI V1 behavior and binary values must be passed literally. When providing contents from a file that map to a binary blob `fileb://` will always be treated as binary and use the file contents directly regardless of the `cli-binary-format` setting. When using `file://` the file contents will need to properly formatted for the configured `cli-binary-format`.

* base64
* raw-in-base64-out

`--no-cli-pager` (boolean)

Disable cli pager for output.

`--cli-auto-prompt` (boolean)

Automatically prompt for CLI input parameters.

`--no-cli-auto-prompt` (boolean)

Disable automatically prompt for CLI input parameters.

`--cli-error-format` (string)

The formatting style for error output. By default, errors are displayed in enhanced format.

* legacy
* json
* yaml
* text
* table
* enhanced

## Examples

#### NOTE
To use the following examples, you must have the AWS CLI installed and configured. See the [Getting started guide](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html) in the *AWS CLI User Guide* for more information.

Unless otherwise stated, all examples have unix-like quotation rules. These examples will need to be adapted to your terminal’s quoting rules. See [Using quotation marks with strings](https://docs.aws.amazon.com/cli/latest/userguide/cli-usage-parameters-quoting-strings.html) in the *AWS CLI User Guide* .

**Example 1: To generate an HMAC for a message**

The following `generate-mac` 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.

In AWS CLI v2, the value of the `message` parameter must be Base64-encoded. Or, you can save the message in a file and use the `fileb://` prefix, which tells the AWS CLI to read binary data from the file.

Before running this command, replace the example key ID with a valid key ID from your AWS account. The key ID must represent a HMAC KMS key with a key usage of `GENERATE_VERIFY_MAC`.

```
msg=(echo 'Hello World' | base64)

aws kms generate-mac \
    --key-id a1b2c3d4-5678-90ab-cdef-EXAMPLE11111 \
    --message fileb://Message \
    --mac-algorithm HMAC_SHA_384
```

Output:

```json
{
    "KeyId": "arn:aws:kms:us-west-2:123456789012:key/a1b2c3d4-5678-90ab-cdef-EXAMPLE11111",
    "Mac": "<HMAC_TAG>",
    "MacAlgorithm": "HMAC_SHA_384"
}
```

For more information about using HMAC KMS keys in AWS KMS, see [HMAC keys in AWS KMS](https://docs.aws.amazon.com/kms/latest/developerguide/hmac.html) in the *AWS Key Management Service Developer Guide*.

**Example 2: To save an HMAC in a file (Linux and macOs)**

The following `generate-mac` example generates an HMAC for a short message stored in a local file. The command also gets the `Mac` property from the response, Base64-decodes it and saves it in the ExampleMac file. You can use the MAC file in a `verify-mac` command that verifies the MAC.

The `generate-mac` command requires a Base64-encoded message and a MAC algorithm that your HMAC KMS key supports. To get the MAC algorithms that your KMS key supports, use the `describe-key` command.

Before running this command, replace the example key ID with a valid key ID from your AWS account. The key ID must represent an asymmetric KMS key with a key usage of GENERATE_VERIFY_MAC.

First, Base64-encode the message and save it in the `EncodedMessage` file.

```
echo 'hello world' | base64 > EncodedMessage
```

Then, generate the HMAC for the encoded message.

```bash
aws kms generate-mac \
    --key-id a1b2c3d4-5678-90ab-cdef-EXAMPLE11111 \
    --message fileb://EncodedMessage \
    --mac-algorithm HMAC_SHA_384 \
    --output text \
    --query Mac | base64 --decode > ExampleMac
```

This command produces no output. This example extracts the `Mac` property of the output and saves it in a file.

For more information about using HMAC KMS keys in AWS KMS, see [HMAC keys in AWS KMS](https://docs.aws.amazon.com/kms/latest/developerguide/hmac.html) in the *AWS Key Management Service Developer Guide*.

## Output

Mac -> (blob)

> The hash-based message authentication code (HMAC) that was generated for the specified message, HMAC KMS key, and MAC algorithm.

> This is the standard, raw HMAC defined in [RFC 2104](https://datatracker.ietf.org/doc/html/rfc2104) .

> Constraints:

> * min: `1`
> * max: `6144`

MacAlgorithm -> (string)

> The MAC algorithm that was used to generate the HMAC.

> Possible values:

> * `HMAC_SHA_224`
> * `HMAC_SHA_256`
> * `HMAC_SHA_384`
> * `HMAC_SHA_512`

KeyId -> (string)

> The HMAC KMS key used in the operation.

> Constraints:

> * min: `1`
> * max: `2048`