# Create an asymmetric KMS key
You can create [asymmetric KMS keys](symmetric-asymmetric.md) in the Amazon KMS console, by using the [CreateKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateKey.html) API, or by using the [AWS::KMS::Key Amazon CloudFormation template](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/aws-resource-kms-key.html). An asymmetric KMS key represents a public and private key pair that can be used for encryption, signing, or deriving shared secrets. The private key remains within Amazon KMS. To download the public key for use outside of Amazon KMS, see [Download public key](download-public-key.md).
When you create an asymmetric KMS key, you must select a key spec. Often the key spec that you select is determined by regulatory, security, or business requirements. It might also be influenced by the size of messages that you need to encrypt or sign. In general, longer encryption keys are more resistant to brute-force attacks. For a detailed description of all supported key specs, see [Key spec reference](symm-asymm-choose-key-spec.md).
Amazon services that integrate with Amazon KMS do not support asymmetric KMS keys. If you want to create a KMS key that encrypts data that you store or manage in an Amazon service, [create a symmetric encryption KMS key](create-symmetric-cmk.md).
For information about the permissions required to create KMS keys, see [Permissions for creating KMS keys](create-keys.md#create-key-permissions).
## Using the Amazon KMS console
You can use the Amazon Web Services Management Console to create asymmetric Amazon KMS keys (KMS keys). Each asymmetric KMS key represents a public and private key pair.
**Important**
Do not include confidential or sensitive information in the alias, description, or tags. These fields may appear in plain text in CloudTrail logs and other output.
1. Sign in to the Amazon Web Services Management Console and open the Amazon Key Management Service (Amazon KMS) console at [https://console.amazonaws.cn/kms](https://console.amazonaws.cn/kms).
1. To change the Amazon Web Services Region, use the Region selector in the upper-right corner of the page.
1. In the navigation pane, choose **Customer managed keys**.
1. Choose **Create key**.
1. To create an asymmetric KMS key, in **Key type,** choose **Asymmetric**.
1. To create an asymmetric KMS key for public key encryption, in **Key usage**, choose **Encrypt and decrypt**.
To create an asymmetric KMS key for signing messages and verifying signatures, in **Key usage**, choose **Sign and verify**.
To create an asymmetric KMS key for deriving shared secrets, in **Key usage**, choose **Key agreement**.
For help choosing a key usage value, see [Choosing what type of KMS key to create](create-keys.md#symm-asymm-choose).
1. Select a specification (**Key spec**) for your asymmetric KMS key.
1. Choose **Next**.
1. Type an [alias](kms-alias.md) for the KMS key. The alias name cannot begin with **aws/**. The **aws/** prefix is reserved by Amazon Web Services to represent Amazon managed keys in your account.
An *alias* is a friendly name that you can use to identify the KMS key in the console and in some Amazon KMS APIs. We recommend that you choose an alias that indicates the type of data you plan to protect or the application you plan to use with the KMS key.
Aliases are required when you create a KMS key in the Amazon Web Services Management Console. You cannot specify an alias when you use the [CreateKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateKey.html) operation, but you can use the console or the [CreateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateAlias.html) operation to create an alias for an existing KMS key. For details, see [Aliases in Amazon KMS](kms-alias.md).
1. (Optional) Type a description for the KMS key.
Enter a description that explains the type of data you plan to protect or the application you plan to use with the KMS key.
You can add a description now or update it any time unless the [key state](key-state.md) is `Pending Deletion` or `Pending Replica Deletion`. To add, change, or delete the description of an existing customer managed key, edit the description on the details page for the KMS key in the Amazon Web Services Management Console or use the [UpdateKeyDescription](https://docs.amazonaws.cn/kms/latest/APIReference/API_UpdateKeyDescription.html) operation.
1. (Optional) Type a tag key and an optional tag value. To add more than one tag to the KMS key, choose **Add tag**.
When you add tags to your Amazon resources, Amazon generates a cost allocation report with usage and costs aggregated by tags. Tags can also be used to control access to a KMS key. For information about tagging KMS keys, see [Tags in Amazon KMS](tagging-keys.md) and [ABAC for Amazon KMS](abac.md).
1. Choose **Next**.
1. Select the IAM users and roles that can administer the KMS key.
**Notes**
This key policy gives the Amazon Web Services account full control of this KMS key. It allows account administrators to use IAM policies to give other principals permission to manage the KMS key. For details, see [Default key policy](key-policy-default.md).
IAM best practices discourage the use of IAM users with long-term credentials. Whenever possible, use IAM roles, which provide temporary credentials. For details, see [Security best practices in IAM](https://docs.aws.amazon.com/IAM/latest/UserGuide/best-practices.html) in the *IAM User Guide*.
The Amazon KMS console adds key administrators to the key policy under the statement identifier `"Allow access for Key Administrators"`. Modifying this statement identifier might impact how the console displays updates that you make to the statement.
1. (Optional) To prevent the selected IAM users and roles from deleting this KMS key, in the **Key deletion** section at the bottom of the page, clear the **Allow key administrators to delete this key** check box.
1. Choose **Next**.
1. Select the IAM users and roles that can use the KMS key for [cryptographic operations](kms-cryptography.md#cryptographic-operations).
**Notes**
IAM best practices discourage the use of IAM users with long-term credentials. Whenever possible, use IAM roles, which provide temporary credentials. For details, see [Security best practices in IAM](https://docs.aws.amazon.com/IAM/latest/UserGuide/best-practices.html) in the *IAM User Guide*.
The Amazon KMS console adds key users to the key policy under the statement identifiers `"Allow use of the key"` and `"Allow attachment of persistent resources"`. Modifying these statement identifiers might impact how the console displays updates that you make to the statement.
1. (Optional) You can allow other Amazon Web Services accounts to use this KMS key for cryptographic operations. To do so, in the **Other Amazon Web Services accounts** section at the bottom of the page, choose **Add another Amazon Web Services account** and enter the Amazon Web Services account identification number of an external account. To add multiple external accounts, repeat this step.
**Note**
To allow principals in the external accounts to use the KMS key, administrators of the external account must create IAM policies that provide these permissions. For more information, see [Allowing users in other accounts to use a KMS key](key-policy-modifying-external-accounts.md).
1. Choose **Next**.
1. Review the key policy statements for the key. To make changes to the key policy, select **Edit**.
1. Choose **Next**.
1. Review the key settings that you chose. You can still go back and change all settings.
1. Choose **Finish** to create the KMS key.
## Using the Amazon KMS API
You can use the [CreateKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateKey.html) operation to create an asymmetric Amazon KMS key. These examples use the [Amazon Command Line Interface (Amazon CLI)](http://www.amazonaws.cn/cli/), but you can use any supported programming language.
When you create an asymmetric KMS key, you must specify the `KeySpec` parameter, which determines the type of keys you create. Also, you must specify a `KeyUsage` value of ENCRYPT\$1DECRYPT, SIGN\$1VERIFY, or KEY\$1AGREEMENT. You cannot change these properties after the KMS key is created.
The `CreateKey` operation doesn't let you specify an alias, but you can use the [CreateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateAlias.html) operation to create an alias for your new KMS key.
**Important**
Do not include confidential or sensitive information in the `Description` or `Tags` fields. These fields may appear in plain text in CloudTrail logs and other output.
**Create an asymmetric KMS key pair for public encryption**
The following example uses the `CreateKey` operation to create an asymmetric KMS key of 4096-bit RSA keys designed for public key encryption.
```
$ aws kms create-key --key-spec RSA_4096 --key-usage ENCRYPT_DECRYPT
{
"KeyMetadata": {
"KeyState": "Enabled",
"KeyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
"KeyManager": "CUSTOMER",
"Description": "",
"Arn": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab",
"CreationDate": 1569973196.214,
"MultiRegion": false,
"KeySpec": "RSA_4096",
"CustomerMasterKeySpec": "RSA_4096",
"KeyUsage": "ENCRYPT_DECRYPT",
"EncryptionAlgorithms": [
"RSAES_OAEP_SHA_1",
"RSAES_OAEP_SHA_256"
],
"AWSAccountId": "111122223333",
"Origin": "AWS_KMS",
"Enabled": true
}
}
```
**Create an asymmetric KMS key pair for signing and verification**
The following example command creates an asymmetric KMS key that represents a pair of ECC keys used for signing and verification. You cannot create an elliptic curve key pair for encryption and decryption.
```
$ aws kms create-key --key-spec ECC_NIST_P521 --key-usage SIGN_VERIFY
{
"KeyMetadata": {
"KeyState": "Enabled",
"KeyId": "0987dcba-09fe-87dc-65ba-ab0987654321",
"CreationDate": 1570824817.837,
"Origin": "AWS_KMS",
"SigningAlgorithms": [
"ECDSA_SHA_512"
],
"Arn": "arn:aws:kms:us-west-2:111122223333:key/0987dcba-09fe-87dc-65ba-ab0987654321",
"AWSAccountId": "111122223333",
"KeySpec": "ECC_NIST_P521",
"CustomerMasterKeySpec": "ECC_NIST_P521",
"KeyManager": "CUSTOMER",
"Description": "",
"Enabled": true,
"MultiRegion": false,
"KeyUsage": "SIGN_VERIFY"
}
}
```
**Create an asymmetric KMS key pair for deriving shared secrets**
The following example command creates an asymmetric KMS key that represents a pair of ECDH keys used for deriving shared secrets. You cannot create an elliptic curve key pair for encryption and decryption.
```
$ aws kms create-key --key-spec ECC_NIST_P256 --key-usage KEY_AGREEMENT
{
"KeyMetadata": {
"AWSAccountId": "111122223333",
"KeyId": "0987dcba-09fe-87dc-65ba-ab0987654321",
"Arn": "arn:aws:kms:us-west-2:111122223333:key/0987dcba-09fe-87dc-65ba-ab0987654321",
"CreationDate": "2023-12-27T19:10:15.063000+00:00",
"Enabled": true,
"Description": "",
"KeyUsage": "KEY_AGREEMENT",
"KeyState": "Enabled",
"Origin": "AWS_KMS",
"KeyManager": "CUSTOMER",
"CustomerMasterKeySpec": "ECC_NIST_P256",
"KeySpec": "ECC_NIST_P256",
"KeyAgreementAlgorithms": [
"ECDH"
],
"MultiRegion": false
}
}
```