AWS SDK Version 3 for .NET
API Reference

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Creates a digital signature for a message or message digest by using the private key in an asymmetric signing KMS key. To verify the signature, use the Verify operation, or use the public key in the same asymmetric KMS key outside of KMS. For information about asymmetric KMS keys, see Asymmetric KMS keys in the Key Management Service Developer Guide.

Digital signatures are generated and verified by using asymmetric key pair, such as an RSA or ECC pair that is represented by an asymmetric KMS key. The key owner (or an authorized user) uses their private key to sign a message. Anyone with the public key can verify that the message was signed with that particular private key and that the message hasn't changed since it was signed.

To use the Sign operation, provide the following information:

When signing a message, be sure to record the KMS key and the signing algorithm. This information is required to verify the signature.

Best practices recommend that you limit the time during which any signature is effective. This deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded. Signatures do not include a timestamp, but you can include a timestamp in the signed message to help you detect when its time to refresh the signature.

To verify the signature that this operation generates, use the Verify operation. Or use the GetPublicKey operation to download the public key and then use the public key to verify the signature outside of KMS.

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:Sign (key policy)

Related operations: Verify


This is an asynchronous operation using the standard naming convention for .NET 4.5 or higher. For .NET 3.5 the operation is implemented as a pair of methods using the standard naming convention of BeginSign and EndSign.

Namespace: Amazon.KeyManagementService
Assembly: AWSSDK.KeyManagementService.dll
Version: 3.x.y.z


public virtual Task<SignResponse> SignAsync(
         SignRequest request,
         CancellationToken cancellationToken
Type: Amazon.KeyManagementService.Model.SignRequest

Container for the necessary parameters to execute the Sign service method.

Type: System.Threading.CancellationToken

A cancellation token that can be used by other objects or threads to receive notice of cancellation.

Return Value
The response from the Sign service method, as returned by KeyManagementService.


DependencyTimeoutException The system timed out while trying to fulfill the request. You can retry the request.
DisabledException The request was rejected because the specified KMS key is not enabled.
InvalidGrantTokenException The request was rejected because the specified grant token is not valid.
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.
KeyUnavailableException The request was rejected because the specified KMS key was not available. You can retry the request.
KMSInternalException The request was rejected because an internal exception occurred. The request can be retried.
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 KMS operation, see Key states of KMS keys in the 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.
NotFoundException The request was rejected because the specified entity or resource could not be found.

Version Information

.NET Core App:
Supported in: 3.1

.NET Standard:
Supported in: 2.0

.NET Framework:
Supported in: 4.5

See Also