VerifyMac - Amazon Key Management Service
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VerifyMac

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 Amazon KMS uses conform to industry standards defined in RFC 2104.

This operation is part of Amazon KMS support for HMAC KMS keys. For details, see HMAC keys in Amazon KMS in the Amazon 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 Amazon KMS keys in the Amazon 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

Request Syntax

{ "GrantTokens": [ "string" ], "KeyId": "string", "Mac": blob, "MacAlgorithm": "string", "Message": blob }

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

The request accepts the following data in JSON format.

Note

In the following list, the required parameters are described first.

KeyId

The KMS key that will be used in the verification.

Enter a key ID of the KMS key that was used to generate the HMAC. If you identify a different KMS key, the VerifyMac operation fails.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

Required: Yes

Mac

The HMAC to verify. Enter the HMAC that was generated by the GenerateMac operation when you specified the same message, HMAC KMS key, and MAC algorithm as the values specified in this request.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 6144.

Required: Yes

MacAlgorithm

The MAC algorithm that will be used in the verification. Enter the same MAC algorithm that was used to compute the HMAC. This algorithm must be supported by the HMAC KMS key identified by the KeyId parameter.

Type: String

Valid Values: HMAC_SHA_224 | HMAC_SHA_256 | HMAC_SHA_384 | HMAC_SHA_512

Required: Yes

Message

The message that will be used in the verification. Enter the same message that was used to generate the HMAC.

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

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 4096.

Required: Yes

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 Amazon Key Management Service Developer Guide.

Type: Array of strings

Array Members: Minimum number of 0 items. Maximum number of 10 items.

Length Constraints: Minimum length of 1. Maximum length of 8192.

Required: No

Response Syntax

{ "KeyId": "string", "MacAlgorithm": "string", "MacValid": boolean }

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

KeyId

The HMAC KMS key used in the verification.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

MacAlgorithm

The MAC algorithm used in the verification.

Type: String

Valid Values: HMAC_SHA_224 | HMAC_SHA_256 | HMAC_SHA_384 | HMAC_SHA_512

MacValid

A Boolean value that indicates whether the HMAC was verified. A value of True indicates that the HMAC (Mac) was generated with the specified Message, HMAC KMS key (KeyID) and MacAlgorithm..

If the HMAC is not verified, the VerifyMac operation fails with a KMSInvalidMacException exception. This exception indicates that one or more of the inputs changed since the HMAC was computed.

Type: Boolean

Errors

For information about the errors that are common to all actions, see Common Errors.

DisabledException

The request was rejected because the specified KMS key is not enabled.

HTTP Status Code: 400

InvalidGrantTokenException

The request was rejected because the specified grant token is not valid.

HTTP Status Code: 400

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.

HTTP Status Code: 400

KeyUnavailableException

The request was rejected because the specified KMS key was not available. You can retry the request.

HTTP Status Code: 500

KMSInternalException

The request was rejected because an internal exception occurred. The request can be retried.

HTTP Status Code: 500

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.

HTTP Status Code: 400

KMSInvalidStateException

The request was rejected because the state of the specified resource is not valid for this request.

For more information about how key state affects the use of a KMS key, see Key states of Amazon KMS keys in the Amazon Key Management Service Developer Guide .

HTTP Status Code: 400

NotFoundException

The request was rejected because the specified entity or resource could not be found.

HTTP Status Code: 400

See Also

For more information about using this API in one of the language-specific Amazon SDKs, see the following: