verify_mac

verify_mac(**kwargs)

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 KMS uses conform to industry standards defined in RFC 2104.

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 .

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:VerifyMac (key policy)

Related operations : GenerateMac

See also: AWS API Documentation

Request Syntax

response = client.verify_mac(
    Message=b'bytes',
    KeyId='string',
    MacAlgorithm='HMAC_SHA_224'|'HMAC_SHA_256'|'HMAC_SHA_384'|'HMAC_SHA_512',
    Mac=b'bytes',
    GrantTokens=[
        'string',
    ]
)

Parameters

• Message (bytes) --

  [REQUIRED]

  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.

• KeyId (string) --

  [REQUIRED]

  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.

• MacAlgorithm (string) --

  [REQUIRED]

  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.

• Mac (bytes) --

  [REQUIRED]

  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.

• GrantTokens (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) --

Return type

dict

Returns

Response Syntax

{
    'KeyId': 'string',
    'MacValid': True|False,
    'MacAlgorithm': 'HMAC_SHA_224'|'HMAC_SHA_256'|'HMAC_SHA_384'|'HMAC_SHA_512'
}

Response Structure

• (dict) --

  • KeyId (string) --

    The HMAC KMS key used in the verification.

  • MacValid (boolean) --

    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.

  • MacAlgorithm (string) --

    The MAC algorithm used in the verification.

Exceptions

• KMS.Client.exceptions.NotFoundException
• KMS.Client.exceptions.DisabledException
• KMS.Client.exceptions.KeyUnavailableException
• KMS.Client.exceptions.InvalidKeyUsageException
• KMS.Client.exceptions.InvalidGrantTokenException
• KMS.Client.exceptions.KMSInternalException
• KMS.Client.exceptions.KMSInvalidMacException
• KMS.Client.exceptions.KMSInvalidStateException

Examples

This example verifies an HMAC for a particular message, HMAC KMS keys, and MAC algorithm. A value of 'true' in the MacValid value in the response indicates that the HMAC is valid.

response = client.verify_mac(
    # The HMAC KMS key input to the HMAC algorithm.
    KeyId='1234abcd-12ab-34cd-56ef-1234567890ab',
    # The HMAC to be verified.
    Mac='<HMAC_TAG>',
    # The HMAC algorithm requested for the operation.
    MacAlgorithm='HMAC_SHA_384',
    # The message input to the HMAC algorithm.
    Message='Hello World',
)

print(response)

Expected Output:

{
    # The key ARN of the HMAC key used in the operation.
    'KeyId': 'arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab',
    # The HMAC algorithm used in the operation.
    'MacAlgorithm': 'HMAC_SHA_384',
    # A value of 'true' indicates that verification succeeded. If verification fails, the call to VerifyMac fails.
    'MacValid': True,
    'ResponseMetadata': {
        '...': '...',
    },
}