Request Syntax Request Parameters Response Syntax Response Elements Errors See Also

Verify

Verifies a digital signature that was generated by the Sign operation.

Verification confirms that an authorized user signed the message with the specified KMS key and signing algorithm, and the message hasn't changed since it was signed. If the signature is verified, the value of the SignatureValid field in the response is True. If the signature verification fails, the Verify operation fails with an KMSInvalidSignatureException exception.

A digital signature is generated by using the private key in an asymmetric KMS key. The signature is verified by using the public key in the same asymmetric KMS key. For information about asymmetric KMS keys, see Asymmetric KMS keys in the AWS Key Management Service Developer Guide.

To use the Verify operation, specify the same asymmetric KMS key, message, and signing algorithm that were used to produce the signature. The message type does not need to be the same as the one used for signing, but it must indicate whether the value of the Message parameter should be hashed as part of the verification process.

You can also verify the digital signature by using the public key of the KMS key outside of AWS KMS. Use the GetPublicKey operation to download the public key in the asymmetric KMS key and then use the public key to verify the signature outside of AWS KMS. The advantage of using the Verify operation is that it is performed within AWS KMS. As a result, it's easy to call, the operation is performed within the FIPS boundary, it is logged in AWS CloudTrail, and you can use key policy and IAM policy to determine who is authorized to use the KMS key to verify signatures.

To verify a signature outside of AWS KMS with an SM2 public key (China Regions only), you must specify the distinguishing ID. By default, AWS KMS uses 1234567812345678 as the distinguishing ID. For more information, see Offline verification with SM2 key pairs.

The KMS key that you use for this operation must be in a compatible key state. For details, see Key states of AWS KMS keys in the AWS Key Management Service Developer Guide.

Cross-account use: Yes. To perform this operation with a KMS key in a different AWS account, specify the key ARN or alias ARN in the value of the KeyId parameter.

Required permissions: kms:Verify (key policy)

Related operations: Sign

Request Syntax


{
   "GrantTokens": [ "string" ],
   "KeyId": "string",
   "Message": blob,
   "MessageType": "string",
   "Signature": blob,
   "SigningAlgorithm": "string"
}

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

Identifies the asymmetric KMS key that will be used to verify the signature. This must be the same KMS key that was used to generate the signature. If you specify a different KMS key, the signature verification fails.

To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a KMS key in a different AWS account, you must use the key ARN or alias ARN.

For example:

Key ID: 1234abcd-12ab-34cd-56ef-1234567890ab
Key ARN: arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
Alias name: alias/ExampleAlias
Alias ARN: arn:aws:kms:us-east-2:111122223333:alias/ExampleAlias

To get the key ID and key ARN for a KMS key, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.

Type: String

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

Required: Yes

Message

Specifies the message that was signed. You can submit a raw message of up to 4096 bytes, or a hash digest of the message. If you submit a digest, use the MessageType parameter with a value of DIGEST.

If the message specified here is different from the message that was signed, the signature verification fails. A message and its hash digest are considered to be the same message.

Type: Base64-encoded binary data object

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

Required: Yes

Signature

The signature that the Sign operation generated.

Type: Base64-encoded binary data object

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

Required: Yes

SigningAlgorithm

The signing algorithm that was used to sign the message. If you submit a different algorithm, the signature verification fails.

Type: String

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 AWS 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

MessageType

Tells AWS KMS whether the value of the Message parameter should be hashed as part of the signing algorithm. Use RAW for unhashed messages; use DIGEST for message digests, which are already hashed.

When the value of MessageType is RAW, AWS KMS uses the standard signing algorithm, which begins with a hash function. When the value is DIGEST, AWS KMS skips the hashing step in the signing algorithm.

Important

Use the DIGEST value only when the value of the Message parameter is a message digest. If you use the DIGEST value with an unhashed message, the security of the verification operation can be compromised.

When the value of MessageTypeis DIGEST, the length of the Message value must match the length of hashed messages for the specified signing algorithm.

You can submit a message digest and omit the MessageType or specify RAW so the digest is hashed again while signing. However, if the signed message is hashed once while signing, but twice while verifying, verification fails, even when the message hasn't changed.

The hashing algorithm in that Verify uses is based on the SigningAlgorithm value.

Signing algorithms that end in SHA_256 use the SHA_256 hashing algorithm.
Signing algorithms that end in SHA_384 use the SHA_384 hashing algorithm.
Signing algorithms that end in SHA_512 use the SHA_512 hashing algorithm.
SM2DSA uses the SM3 hashing algorithm. For details, see Offline verification with SM2 key pairs.

Type: String

Valid Values: RAW | DIGEST

Required: No

Response Syntax


{
   "KeyId": "string",
   "SignatureValid": boolean,
   "SigningAlgorithm": "string"
}

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 Amazon Resource Name (key ARN) of the asymmetric KMS key that was used to verify the signature.

Type: String

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

SignatureValid

A Boolean value that indicates whether the signature was verified. A value of True indicates that the Signature was produced by signing the Message with the specified KeyID and SigningAlgorithm. If the signature is not verified, the Verify operation fails with a KMSInvalidSignatureException exception.

Type: Boolean

SigningAlgorithm

The signing algorithm that was used to verify the signature.

Type: String

Errors

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

DependencyTimeoutException

The system timed out while trying to fulfill the request. You can retry the request.

HTTP Status Code: 500

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

KMSInvalidSignatureException

The request was rejected because the signature verification failed. Signature verification fails when it cannot confirm that signature was produced by signing the specified message with the specified KMS key and signing algorithm.

HTTP Status Code: 400

KMSInvalidStateException

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

This exceptions means one of the following:

The key state of the KMS key is not compatible with the operation.

To find the key state, use the DescribeKey operation. For more information about which key states are compatible with each AWS KMS operation, see Key states of AWS KMS keys in the AWS Key Management Service Developer Guide .
For cryptographic operations on KMS keys in custom key stores, this exception represents a general failure with many possible causes. To identify the cause, see the error message that accompanies the exception.

HTTP Status Code: 400

NotFoundException

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

HTTP Status Code: 400