[ aws . kms ]

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

You can use the HMAC that this operation generates with 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. 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 * .

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deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded.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

See also: AWS API Documentation

See ‘aws help’ for descriptions of global parameters.

Synopsis

  generate-mac
--message <value>
--key-id <value>
--mac-algorithm <value>
[--grant-tokens <value>]
[--cli-input-json | --cli-input-yaml]
[--generate-cli-skeleton <value>]

Options

--message (blob)

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.

--key-id (string)

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.

--mac-algorithm (string)

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 and Using a grant token in the Key Management Service Developer Guide .

(string)

Syntax:

"string" "string" ...

--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.

See ‘aws help’ for descriptions of global parameters.

Output

Mac -> (blob)

The hash-based message authentication code (HMAC) for the given message, key, and MAC algorithm.

MacAlgorithm -> (string)

The MAC algorithm that was used to generate the HMAC.

KeyId -> (string)

The HMAC KMS key used in the operation.