GetPublicKey
Returns the public key of an asymmetric CMK. Unlike the private key of a asymmetric
CMK,
which never leaves AWS KMS unencrypted, callers with kms:GetPublicKey
permission
can download the public key of an asymmetric CMK. You can share the public key to
allow others
to encrypt messages and verify signatures outside of AWS KMS. For information about
symmetric and asymmetric CMKs, see Using Symmetric and Asymmetric CMKs 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 CMK. 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. For details, see Special Considerations for Downloading Public Keys.
To help you use the public key safely outside of AWS KMS, GetPublicKey
returns
important information about the public key in the response, including:
-
CustomerMasterKeySpec: The type of key material in the public key, such as
RSA_4096
orECC_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 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.
The CMK that you use for this operation must be in a compatible key state. For details, see Key state: Effect on your CMK in the AWS Key Management Service Developer Guide.
Cross-account use: Yes. To perform this operation with a CMK 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
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.
In the following list, the required parameters are described first.
- KeyId
-
Identifies the asymmetric CMK that includes the public key.
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
-
- 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" ],
"KeyId": "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
-
The type of the of the public key that was downloaded.
Type: String
Valid Values:
RSA_2048 | RSA_3072 | RSA_4096 | ECC_NIST_P256 | ECC_NIST_P384 | ECC_NIST_P521 | ECC_SECG_P256K1 | SYMMETRIC_DEFAULT
- 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 isENCRYPT_DECRYPT
.Type: Array of strings
Valid Values:
SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256
- KeyId
-
The Amazon Resource Name (key ARN) of the asymmetric CMK from which the public key was downloaded.
Type: String
Length Constraints: Minimum length of 1. Maximum length of 2048.
- KeyUsage
-
The permitted use of the public key. Valid values are
ENCRYPT_DECRYPT
orSIGN_VERIFY
.This information is critical. 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
- 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 isSIGN_VERIFY
.Type: Array of strings
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
- 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 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 beENCRYPT_DECRYPT
. For signing and verifying, theKeyUsage
must beSIGN_VERIFY
. To find theKeyUsage
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
- 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
- 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
See Also
For more information about using this API in one of the language-specific AWS SDKs, see the following: