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Returns the public key of an asymmetric KMS key. Unlike the private key of a asymmetric
KMS key, which never leaves KMS unencrypted, callers with kms:GetPublicKey
permission can download the public key of an asymmetric KMS key. You can share the
public key to allow others to encrypt messages and verify signatures outside of KMS.
For information about asymmetric KMS keys, see Asymmetric
KMS keys in the Key Management Service Developer Guide.
You do not need to download the public key. Instead, you can use the public key within KMS by calling the Encrypt, ReEncrypt, or Verify operations with the identifier of an asymmetric KMS key. When you use the public key within KMS, you benefit from the authentication, authorization, and logging that are part of every KMS operation. You also reduce of risk of encrypting data that cannot be decrypted. These features are not effective outside of KMS.
To help you use the public key safely outside of KMS, GetPublicKey returns
important information about the public key in the response, including:
KeySpec:
The type of key material in the public key, such as RSA_4096 or ECC_NIST_P521.
KeyUsage: Whether the key is used for encryption or signing.
EncryptionAlgorithms or SigningAlgorithms: A list of the encryption algorithms or the signing algorithms for the key.
Although KMS cannot enforce these restrictions on external operations, it is crucial that you use this information to prevent the public key from being used improperly. For example, you can prevent a public signing key from being used encrypt data, or prevent a public key from being used with an encryption algorithm that is not supported by KMS. You can also avoid errors, such as using the wrong signing algorithm in a verification operation.
To verify a signature outside of KMS with an SM2 public key (China Regions only),
you must specify the distinguishing ID. By default, 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 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:GetPublicKey (key policy)
Related operations: CreateKey
Eventual consistency: The KMS API follows an eventual consistency model. For more information, see KMS eventual consistency.
For .NET Core this operation is only available in asynchronous form. Please refer to GetPublicKeyAsync.
Namespace: Amazon.KeyManagementService
Assembly: AWSSDK.KeyManagementService.dll
Version: 3.x.y.z
public virtual GetPublicKeyResponse GetPublicKey( GetPublicKeyRequest request )
Container for the necessary parameters to execute the GetPublicKey service method.
| Exception | Condition |
|---|---|
| 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. |
| InvalidArnException | The request was rejected because a specified ARN, or an ARN in a key policy, is not valid. |
| 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. |
| UnsupportedOperationException | The request was rejected because a specified parameter is not supported or a specified resource is not valid for this operation. |
This example gets the public key of an asymmetric RSA KMS key used for encryption and decryption. The operation returns the key spec, key usage, and encryption or signing algorithms to help you use the public key correctly outside of AWS KMS.
var client = new AmazonKeyManagementServiceClient();
var response = client.GetPublicKey(new GetPublicKeyRequest
{
KeyId = "arn:aws:kms:us-west-2:111122223333:key/0987dcba-09fe-87dc-65ba-ab0987654321" // The key ARN of the asymmetric KMS key.
});
string customerMasterKeySpec = response.CustomerMasterKeySpec; // The key spec of the asymmetric KMS key from which the public key was downloaded.
List<string> encryptionAlgorithms = response.EncryptionAlgorithms; // The encryption algorithms supported by the asymmetric KMS key that was downloaded.
string keyId = response.KeyId; // The key ARN of the asymmetric KMS key from which the public key was downloaded.
string keyUsage = response.KeyUsage; // The key usage of the asymmetric KMS key from which the public key was downloaded.
MemoryStream publicKey = response.PublicKey; // The public key (plaintext) of the asymmetric KMS key.
.NET Framework:
Supported in: 4.5, 4.0, 3.5