Request Syntax Request Parameters Response Syntax Response Elements Errors See Also

GetPublicKey

Returns the public key of an asymmetric KMS key. Unlike the private key of a asymmetric KMS key, which never leaves AWS 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 AWS KMS. For information about asymmetric KMS keys, see Asymmetric KMS keys in the AWS Key Management Service Developer Guide.

You do not need to download the public key. Instead, you can use the public key within AWS KMS by calling the Encrypt, ReEncrypt, or Verify operations with the identifier of an asymmetric KMS key. When you use the public key within AWS KMS, you benefit from the authentication, authorization, and logging that are part of every AWS KMS operation. You also reduce of risk of encrypting data that cannot be decrypted. These features are not effective outside of AWS KMS.

To help you use the public key safely outside of AWS 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, signing, or deriving a shared secret.
EncryptionAlgorithms, KeyAgreementAlgorithms, or SigningAlgorithms: A list of the encryption algorithms, key agreement algorithms, or signing algorithms for the key.

Although AWS 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 AWS KMS. You can also avoid errors, such as using the wrong signing algorithm in a verification operation.

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:GetPublicKey (key policy)

Related operations: CreateKey

Eventual consistency: The AWS KMS API follows an eventual consistency model. For more information, see AWS KMS eventual consistency.

Request Syntax


{
   "GrantTokens": [ "string" ],
   "KeyId": "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 includes the public key.

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

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

Response Syntax


{
   "CustomerMasterKeySpec": "string",
   "EncryptionAlgorithms": [ "string" ],
   "KeyAgreementAlgorithms": [ "string" ],
   "KeyId": "string",
   "KeySpec": "string",
   "KeyUsage": "string",
   "PublicKey": blob,
   "SigningAlgorithms": [ "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.

CustomerMasterKeySpec

This parameter has been deprecated.

Instead, use the KeySpec field in the GetPublicKey response.

The KeySpec and CustomerMasterKeySpec fields have the same value. We recommend that you use the KeySpec field in your code. However, to avoid breaking changes, AWS KMS supports both fields.

Type: String

EncryptionAlgorithms

The encryption algorithms that AWS KMS supports for this key.

This information is critical. If a public key encrypts data outside of AWS KMS by using an unsupported encryption algorithm, the ciphertext cannot be decrypted.

This field appears in the response only when the KeyUsage of the public key is ENCRYPT_DECRYPT.

Type: Array of strings

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256 | SM2PKE

KeyAgreementAlgorithms

The key agreement algorithm used to derive a shared secret. This field is present only when the KMS key has a KeyUsage value of KEY_AGREEMENT.

Type: Array of strings

Valid Values: ECDH

KeyId

The Amazon Resource Name (key ARN) of the asymmetric KMS key from which the public key was downloaded.

Type: String

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

KeySpec

The type of the of the public key that was downloaded.

Type: String

KeyUsage

The permitted use of the public key. Valid values for asymmetric key pairs are ENCRYPT_DECRYPT, SIGN_VERIFY, and KEY_AGREEMENT.

This information is critical. For example, if a public key with SIGN_VERIFY key usage encrypts data outside of AWS KMS, the ciphertext cannot be decrypted.

Type: String

Valid Values: SIGN_VERIFY | ENCRYPT_DECRYPT | GENERATE_VERIFY_MAC | KEY_AGREEMENT

PublicKey

The exported public key.

The value is a DER-encoded X.509 public key, also known as SubjectPublicKeyInfo (SPKI), as defined in RFC 5280. When you use the HTTP API or the AWS CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 8192.

SigningAlgorithms

The signing algorithms that AWS KMS supports for this key.

This field appears in the response only when the KeyUsage of the public key is SIGN_VERIFY.

Type: Array of strings

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

InvalidArnException

The request was rejected because a specified ARN, or an ARN in a key policy, is not valid.

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. For deriving key agreement secrets, the KeyUsage must be KEY_AGREEMENT. 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

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

UnsupportedOperationException

The request was rejected because a specified parameter is not supported or a specified resource is not valid for this operation.

HTTP Status Code: 400