# Aliases in Amazon KMS
An *alias* is a friendly name for a Amazon KMS key. For example, an alias lets you refer to a KMS key as `test-key` instead of `1234abcd-12ab-34cd-56ef-1234567890ab`.
You can use an alias to identify a KMS key in the Amazon KMS console, in the [DescribeKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_DescribeKey.html) operation, and in [cryptographic operations](kms-cryptography.md#cryptographic-operations), such as [Encrypt](https://docs.amazonaws.cn/kms/latest/APIReference/API_Encrypt.html) and [GenerateDataKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_GenerateDataKey.html). Aliases also make it easy to recognize an [Amazon managed key](concepts.md#aws-managed-key). Aliases for these KMS keys always have the form `aws/`. For example, the alias for the Amazon managed key for Amazon DynamoDB is `aws/dynamodb`. You can establish similar alias standards for your projects, such as prefacing your aliases with the name of a project or category.
You can also allow and deny access to KMS keys based on their aliases without editing policies or managing grants. This feature is part of Amazon KMS support for [attribute-based access control](abac.md) (ABAC). For details, see [Use aliases to control access to KMS keys](alias-authorization.md).
Much of the power of aliases come from your ability to change the KMS key associated with an alias at any time. Aliases can make your code easier to write and maintain. For example, suppose you use an alias to refer to a particular KMS key and you want to change the KMS key. In that case, just associate the alias with a different KMS key. You don't need to change your code.
Aliases also make it easier to reuse the same code in different Amazon Web Services Regions. Create aliases with the same name in multiple Regions and associate each alias with a KMS key in its Region. When the code runs in each Region, the alias refers to the associated KMS key in that Region. For an example, see [Learn how to use aliases in your applications](alias-using.md).
You can create an alias for a KMS key in the Amazon KMS console, by using the [CreateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateAlias.html) API, or by using the [AWS::KMS::Alias Amazon CloudFormation template](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/aws-resource-kms-alias.html).
The Amazon KMS API provides full control of aliases in each account and Region. The API includes operations to create an alias ([CreateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateAlias.html)), view alias names and alias ARNs ([ListAliases](https://docs.amazonaws.cn/kms/latest/APIReference/API_ListAliases.html)), change the KMS key associated with an alias ([UpdateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_UpdateAlias.html)), and delete an alias ([DeleteAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_DeleteAlias.html)).
## How aliases work
Learn how aliases work in Amazon KMS.
**An alias is an independent Amazon resource**
An alias is not a property of a KMS key. The actions that you take on the alias don't affect its associated KMS key. You can create an alias for a KMS key and then update the alias so it's associated with a different KMS key. You can even delete the alias without any effect on the associated KMS key. However, if you delete a KMS key, all aliases associated with that KMS key are deleted.
If you specify an alias as the resource in an IAM policy, the policy refers to the alias, not to the associated KMS key.
**Each alias has two formats**
When you create an alias, you specify the alias name. Amazon KMS creates the alias ARN for you.
+ An [alias ARN](concepts.md#key-id-alias-ARN) is an Amazon Resource Name (ARN) that uniquely identifies the alias.
```
# Alias ARN
arn:aws:kms:us-west-2:111122223333:alias/
```
+ An [alias name](concepts.md#key-id-alias-name) that is unique in the account and Region. In the Amazon KMS API, the alias name is always prefixed by `alias/`. That prefix is omitted in the Amazon KMS console.
```
# Alias name
alias/
```
**Aliases are not secret**
Aliases may be displayed in plaintext in CloudTrail logs and other output. Do not include confidential or sensitive information in the alias name.
**Each alias is associated with one KMS key at a time**
The alias and its KMS key must be in the same account and Region.
You can associate an alias with any [customer managed key](concepts.md#customer-mgn-key) in the same Amazon Web Services account and Region. However, you do not have permission to associate an alias with an [Amazon managed key](concepts.md#aws-managed-key).
For example, this [ListAliases](https://docs.amazonaws.cn/kms/latest/APIReference/API_ListAliases.html) output shows that the `test-key` alias is associated with exactly one target KMS key, which is represented by the `TargetKeyId` property.
```
{
"AliasName": "alias/test-key",
"AliasArn": "arn:aws:kms:us-west-2:111122223333:alias/test-key",
"TargetKeyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
"CreationDate": 1593622000.191,
"LastUpdatedDate": 1593622000.191
}
```
**Multiple aliases can be associated with the same KMS key**
For example, you can associate the `test-key` and `project-key` aliases with the same KMS key.
```
{
"AliasName": "alias/test-key",
"AliasArn": "arn:aws:kms:us-west-2:111122223333:alias/test-key",
"TargetKeyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
"CreationDate": 1593622000.191,
"LastUpdatedDate": 1593622000.191
},
{
"AliasName": "alias/project-key",
"AliasArn": "arn:aws:kms:us-west-2:111122223333:alias/project-key",
"TargetKeyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
"CreationDate": 1516435200.399,
"LastUpdatedDate": 1516435200.399
}
```
**An alias must be unique in an account and Region**
For example, you can have only one `test-key` alias in each account and Region. Aliases are case-sensitive, but aliases that differ only in their capitalization are very prone to error. You cannot change an alias name. However, you can delete the alias and create a new alias with the desired name.
**You can create an alias with the same name in different Regions**
For example, you can have a `finance-key` alias in US East (N. Virginia) and a `finance-key` alias in Europe (Frankfurt). Each alias would be associated with a KMS key in its Region. If your code refers to an alias name like `alias/finance-key`, you can run it in multiple Regions. In each Region, it uses a different KMS key. For details, see [Learn how to use aliases in your applications](alias-using.md).
**You can change the KMS key associated with an alias**
You can use the [UpdateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_UpdateAlias.html) operation to associate an alias with a different KMS key. For example, if the `finance-key` alias is associated with the `1234abcd-12ab-34cd-56ef-1234567890ab` KMS key, you can update it so it is associated with the `0987dcba-09fe-87dc-65ba-ab0987654321` KMS key.
However, the current and new KMS key must be the same type (both symmetric or both asymmetric or both HMAC), and they must have the same [key usage](create-keys.md#key-usage) (ENCRYPT\$1DECRYPT or SIGN\$1VERIFY or GENERATE\$1VERIFY\$1MAC). This restriction prevents errors in code that uses aliases. If you must associate an alias with a different type of key, and you have mitigated the risks, you can delete and recreate the alias.
**Some KMS keys don't have aliases**
When you create a KMS key in the Amazon KMS console, you must give it a new alias. But an alias is not required when you use the [CreateKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_CreateKey.html) operation to create a KMS key. Also, you can use the [UpdateAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_UpdateAlias.html) operation to change the KMS key associated with an alias and the [DeleteAlias](https://docs.amazonaws.cn/kms/latest/APIReference/API_DeleteAlias.html) operation to delete an alias. As a result, some KMS keys might have several aliases, and some might have none.
**Amazon creates aliases in your account**
Amazon creates aliases in your account for [Amazon managed keys](concepts.md#aws-managed-key). These aliases have names of the form `alias/aws/`, such as `alias/aws/s3`.
Some Amazon aliases have no KMS key. These predefined aliases are usually associated with an Amazon managed key when you start using the service.
**Use aliases to identify KMS keys**
You can use an [alias name](concepts.md#key-id-alias-name) or [alias ARN](concepts.md#key-id-alias-ARN) to identify a KMS key in [cryptographic operations](kms-cryptography.md#cryptographic-operations), [DescribeKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_DescribeKey.html), and [GetPublicKey](https://docs.amazonaws.cn/kms/latest/APIReference/API_GetPublicKey.html). (If the [KMS key is in a different Amazon Web Services account](key-policy-modifying-external-accounts.md), you must use its [key ARN](concepts.md#key-id-key-ARN) or alias ARN.) Aliases are not valid identifiers for KMS keys in other Amazon KMS operations. For information about the valid [key identifiers](concepts.md#key-id) for each Amazon KMS API operation, see the descriptions of the `KeyId` parameters in the *Amazon Key Management Service API Reference*.
You cannot use an alias name or alias ARN to [identify a KMS key in an IAM policy](cmks-in-iam-policies.md). To control access to a KMS key based on its aliases, use the [kms:RequestAlias](conditions-kms.md#conditions-kms-request-alias) or [kms:ResourceAliases](conditions-kms.md#conditions-kms-resource-aliases) condition keys. For details, see [ABAC for Amazon KMS](abac.md).