Verify - AWS Key Management Service

Verify

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

Verification confirms that an authorized user signed the message with the specified CMK 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 CMK. The signature is verified by using the public key in the same asymmetric CMK. For information about symmetric and asymmetric CMKs, see Using Symmetric and Asymmetric CMKs in the AWS Key Management Service Developer Guide.

To verify a digital signature, you can use the Verify operation. Specify the same asymmetric CMK, message, and signing algorithm that were used to produce the signature.

You can also verify the digital signature by using the public key of the CMK outside of AWS KMS. Use the GetPublicKey operation to download the public key in the asymmetric CMK 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 CMK to verify signatures.

The CMK that you use for this operation must be in a compatible key state. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide.

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

To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a CMK 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 CMK, 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

Valid Values: RSASSA_PSS_SHA_256 | RSASSA_PSS_SHA_384 | RSASSA_PSS_SHA_512 | RSASSA_PKCS1_V1_5_SHA_256 | RSASSA_PKCS1_V1_5_SHA_384 | RSASSA_PKCS1_V1_5_SHA_512 | ECDSA_SHA_256 | ECDSA_SHA_384 | ECDSA_SHA_512

Required: Yes

GrantTokens

A list of grant tokens.

For more information, see Grant Tokens 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 is a message or message digest. The default value, RAW, indicates a message. To indicate a message digest, enter DIGEST.

Important

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

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 CMK 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

Valid Values: RSASSA_PSS_SHA_256 | RSASSA_PSS_SHA_384 | RSASSA_PSS_SHA_512 | RSASSA_PKCS1_V1_5_SHA_256 | RSASSA_PKCS1_V1_5_SHA_384 | RSASSA_PKCS1_V1_5_SHA_512 | ECDSA_SHA_256 | ECDSA_SHA_384 | ECDSA_SHA_512

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. The request can be retried.

HTTP Status Code: 500

DisabledException

The request was rejected because the specified CMK 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 CMK 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 CMK (CustomerMasterKeySpec).

For encrypting, decrypting, re-encrypting, and generating data keys, the KeyUsage must be ENCRYPT_DECRYPT. For signing and verifying, the KeyUsage must be SIGN_VERIFY. To find the KeyUsage of a CMK, use the DescribeKey operation.

To find the encryption or signing algorithms supported for a particular CMK, use the DescribeKey operation.

HTTP Status Code: 400

KeyUnavailableException

The request was rejected because the specified CMK 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 CMK 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.

For more information about how key state affects the use of a CMK, see How Key State Affects Use of a Customer Master Key in the AWS 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 AWS SDKs, see the following: