AWS.KMS

AWS Key Management Service

AWS Key Management Service (KMS) is an encryption and key management web service. This guide describes the KMS actions that you can call programmatically. For general information about KMS, see the AWS Key Management Service Developer Guide

AWS provides SDKs that consist of libraries and sample code for various programming languages and platforms (Java, Ruby, .Net, iOS, Android, etc.). The SDKs provide a convenient way to create programmatic access to KMS and AWS. For example, the SDKs take care of tasks such as signing requests (see below), managing errors, and retrying requests automatically. For more information about the AWS SDKs, including how to download and install them, see Tools for Amazon Web Services.

We recommend that you use the AWS SDKs to make programmatic API calls to KMS.

Clients must support TLS (Transport Layer Security) 1.0. We recommend TLS 1.2. Clients must also support cipher suites with Perfect Forward Secrecy (PFS) such as Ephemeral Diffie-Hellman (DHE) or Elliptic Curve Ephemeral Diffie-Hellman (ECDHE). Most modern systems such as Java 7 and later support these modes.

Signing Requests

Requests must be signed by using an access key ID and a secret access key. We strongly recommend that you do not use your AWS account access key ID and secret key for everyday work with KMS. Instead, use the access key ID and secret access key for an IAM user, or you can use the AWS Security Token Service to generate temporary security credentials that you can use to sign requests.

All KMS operations require Signature Version 4.

Recording API Requests

KMS supports AWS CloudTrail, a service that records AWS API calls and related events for your AWS account and delivers them to an Amazon S3 bucket that you specify. By using the information collected by CloudTrail, you can determine what requests were made to KMS, who made the request, when it was made, and so on. To learn more about CloudTrail, including how to turn it on and find your log files, see the AWS CloudTrail User Guide

Additional Resources

For more information about credentials and request signing, see the following:

Commonly Used APIs

Of the APIs discussed in this guide, the following will prove the most useful for most applications. You will likely perform actions other than these, such as creating keys and assigning policies, by using the console.

Summary

create_alias(client, input, options \\ [])

Creates a display name for a customer master key. An alias can be used to identify a key and should be unique. The console enforces a one-to-one mapping between the alias and a key. An alias name can contain only alphanumeric characters, forward slashes (/), underscores (_), and dashes (-). An alias must start with the word "alias" followed by a forward slash (alias/). An alias that begins with "aws" after the forward slash (alias/aws...) is reserved by Amazon Web Services (AWS)

create_grant(client, input, options \\ []) Adds a grant to a key to specify who can access the key and under what conditions. Grants are alternate permission mechanisms to key policies. For more information about grants, see Grants in the developer guide. If a grant is absent, access to the key is evaluated based on IAM policies attached to the user.
  1. ListGrants
  2. RetireGrant
  3. RevokeGrant
create_key(client, input, options \\ [])

Creates a customer master key. Customer master keys can be used to encrypt small amounts of data (less than 4K) directly, but they are most commonly used to encrypt or envelope data keys that are then used to encrypt customer data. For more information about data keys, see GenerateDataKey and GenerateDataKeyWithoutPlaintext

decrypt(client, input, options \\ []) Decrypts ciphertext. Ciphertext is plaintext that has been previously encrypted by using any of the following functions:
  • GenerateDataKey
  • GenerateDataKeyWithoutPlaintext
  • Encrypt
delete_alias(client, input, options \\ [])

Deletes the specified alias. To associate an alias with a different key, call UpdateAlias

describe_key(client, input, options \\ [])

Provides detailed information about the specified customer master key

disable_key(client, input, options \\ [])

Marks a key as disabled, thereby preventing its use

disable_key_rotation(client, input, options \\ [])

Disables rotation of the specified key

enable_key(client, input, options \\ [])

Marks a key as enabled, thereby permitting its use. You can have up to 25 enabled keys at one time

enable_key_rotation(client, input, options \\ [])

Enables rotation of the specified customer master key

encrypt(client, input, options \\ []) Encrypts plaintext into ciphertext by using a customer master key. The Encrypt function has two primary use cases:
  • You can encrypt up to 4 KB of arbitrary data such as an RSA key, a database password, or other sensitive customer information.
  • If you are moving encrypted data from one region to another, you can use this API to encrypt in the new region the plaintext data key that was used to encrypt the data in the original region. This provides you with an encrypted copy of the data key that can be decrypted in the new region and used there to decrypt the encrypted data.
generate_data_key(client, input, options \\ [])

Generates a data key that you can use in your application to locally encrypt data. This call returns a plaintext version of the key in the Plaintext field of the response object and an encrypted copy of the key in the CiphertextBlob field. The key is encrypted by using the master key specified by the KeyId field. To decrypt the encrypted key, pass it to the Decrypt API

generate_data_key_without_plaintext(client, input, options \\ [])

Returns a data key encrypted by a customer master key without the plaintext copy of that key. Otherwise, this API functions exactly like GenerateDataKey. You can use this API to, for example, satisfy an audit requirement that an encrypted key be made available without exposing the plaintext copy of that key

generate_random(client, input, options \\ [])

Generates an unpredictable byte string

get_key_policy(client, input, options \\ [])

Retrieves a policy attached to the specified key

get_key_rotation_status(client, input, options \\ [])

Retrieves a Boolean value that indicates whether key rotation is enabled for the specified key

list_aliases(client, input, options \\ [])

Lists all of the key aliases in the account

list_grants(client, input, options \\ [])

List the grants for a specified key

list_key_policies(client, input, options \\ [])

Retrieves a list of policies attached to a key

list_keys(client, input, options \\ [])

Lists the customer master keys

put_key_policy(client, input, options \\ [])

Attaches a policy to the specified key

re_encrypt(client, input, options \\ [])

Encrypts data on the server side with a new customer master key without exposing the plaintext of the data on the client side. The data is first decrypted and then encrypted. This operation can also be used to change the encryption context of a ciphertext

retire_grant(client, input, options \\ []) Retires a grant. You can retire a grant when you're done using it to clean up. You should revoke a grant when you intend to actively deny operations that depend on it. The following are permitted to call this API:
  • The account that created the grant
  • The RetiringPrincipal, if present
  • The GranteePrincipal, if RetireGrant is a grantee operation

The grant to retire must be identified by its grant token or by a combination of the key ARN and the grant ID. A grant token is a unique variable-length base64-encoded string. A grant ID is a 64 character unique identifier of a grant. Both are returned by the CreateGrant function

revoke_grant(client, input, options \\ [])

Revokes a grant. You can revoke a grant to actively deny operations that depend on it

update_alias(client, input, options \\ [])

Updates an alias to associate it with a different key

update_key_description(client, input, options \\ [])

Updates the description of a key

Functions

create_alias(client, input, options \\ [])

Creates a display name for a customer master key. An alias can be used to identify a key and should be unique. The console enforces a one-to-one mapping between the alias and a key. An alias name can contain only alphanumeric characters, forward slashes (/), underscores (_), and dashes (-). An alias must start with the word "alias" followed by a forward slash (alias/). An alias that begins with "aws" after the forward slash (alias/aws...) is reserved by Amazon Web Services (AWS).

To associate an alias with a different key, call UpdateAlias.

Note that you cannot create or update an alias that represents a key in another account.

create_grant(client, input, options \\ [])
Adds a grant to a key to specify who can access the key and under what conditions. Grants are alternate permission mechanisms to key policies. For more information about grants, see Grants in the developer guide. If a grant is absent, access to the key is evaluated based on IAM policies attached to the user.
  1. ListGrants
  2. RetireGrant
  3. RevokeGrant
create_key(client, input, options \\ [])

Creates a customer master key. Customer master keys can be used to encrypt small amounts of data (less than 4K) directly, but they are most commonly used to encrypt or envelope data keys that are then used to encrypt customer data. For more information about data keys, see GenerateDataKey and GenerateDataKeyWithoutPlaintext.

decrypt(client, input, options \\ [])
Decrypts ciphertext. Ciphertext is plaintext that has been previously encrypted by using any of the following functions:
  • GenerateDataKey
  • GenerateDataKeyWithoutPlaintext
  • Encrypt

Note that if a caller has been granted access permissions to all keys (through, for example, IAM user policies that grant Decrypt permission on all resources), then ciphertext encrypted by using keys in other accounts where the key grants access to the caller can be decrypted. To remedy this, we recommend that you do not grant Decrypt access in an IAM user policy. Instead grant Decrypt access only in key policies. If you must grant Decrypt access in an IAM user policy, you should scope the resource to specific keys or to specific trusted accounts.

delete_alias(client, input, options \\ [])

Deletes the specified alias. To associate an alias with a different key, call UpdateAlias.

describe_key(client, input, options \\ [])

Provides detailed information about the specified customer master key.

disable_key(client, input, options \\ [])

Marks a key as disabled, thereby preventing its use.

disable_key_rotation(client, input, options \\ [])

Disables rotation of the specified key.

enable_key(client, input, options \\ [])

Marks a key as enabled, thereby permitting its use. You can have up to 25 enabled keys at one time.

enable_key_rotation(client, input, options \\ [])

Enables rotation of the specified customer master key.

encrypt(client, input, options \\ [])
Encrypts plaintext into ciphertext by using a customer master key. The Encrypt function has two primary use cases:
  • You can encrypt up to 4 KB of arbitrary data such as an RSA key, a database password, or other sensitive customer information.
  • If you are moving encrypted data from one region to another, you can use this API to encrypt in the new region the plaintext data key that was used to encrypt the data in the original region. This provides you with an encrypted copy of the data key that can be decrypted in the new region and used there to decrypt the encrypted data.

Unless you are moving encrypted data from one region to another, you don't use this function to encrypt a generated data key within a region. You retrieve data keys already encrypted by calling the GenerateDataKey or GenerateDataKeyWithoutPlaintext function. Data keys don't need to be encrypted again by calling Encrypt.

If you want to encrypt data locally in your application, you can use the GenerateDataKey function to return a plaintext data encryption key and a copy of the key encrypted under the customer master key (CMK) of your choosing.

generate_data_key(client, input, options \\ [])

Generates a data key that you can use in your application to locally encrypt data. This call returns a plaintext version of the key in the Plaintext field of the response object and an encrypted copy of the key in the CiphertextBlob field. The key is encrypted by using the master key specified by the KeyId field. To decrypt the encrypted key, pass it to the Decrypt API.

We recommend that you use the following pattern to locally encrypt data: call the GenerateDataKey API, use the key returned in the Plaintext response field to locally encrypt data, and then erase the plaintext data key from memory. Store the encrypted data key (contained in the CiphertextBlob field) alongside of the locally encrypted data.

You should not call the Encrypt function to re-encrypt your data keys within a region. GenerateDataKey always returns the data key encrypted and tied to the customer master key that will be used to decrypt it. There is no need to decrypt it twice.

If you decide to use the optional EncryptionContext parameter, you must also store the context in full or at least store enough information along with the encrypted data to be able to reconstruct the context when submitting the ciphertext to the Decrypt API. It is a good practice to choose a context that you can reconstruct on the fly to better secure the ciphertext. For more information about how this parameter is used, see Encryption Context.

To decrypt data, pass the encrypted data key to the Decrypt API. Decrypt uses the associated master key to decrypt the encrypted data key and returns it as plaintext. Use the plaintext data key to locally decrypt your data and then erase the key from memory. You must specify the encryption context, if any, that you specified when you generated the key. The encryption context is logged by CloudTrail, and you can use this log to help track the use of particular data.

generate_data_key_without_plaintext(client, input, options \\ [])

Returns a data key encrypted by a customer master key without the plaintext copy of that key. Otherwise, this API functions exactly like GenerateDataKey. You can use this API to, for example, satisfy an audit requirement that an encrypted key be made available without exposing the plaintext copy of that key.

generate_random(client, input, options \\ [])

Generates an unpredictable byte string.

get_key_policy(client, input, options \\ [])

Retrieves a policy attached to the specified key.

get_key_rotation_status(client, input, options \\ [])

Retrieves a Boolean value that indicates whether key rotation is enabled for the specified key.

list_aliases(client, input, options \\ [])

Lists all of the key aliases in the account.

list_grants(client, input, options \\ [])

List the grants for a specified key.

list_key_policies(client, input, options \\ [])

Retrieves a list of policies attached to a key.

list_keys(client, input, options \\ [])

Lists the customer master keys.

put_key_policy(client, input, options \\ [])

Attaches a policy to the specified key.

re_encrypt(client, input, options \\ [])

Encrypts data on the server side with a new customer master key without exposing the plaintext of the data on the client side. The data is first decrypted and then encrypted. This operation can also be used to change the encryption context of a ciphertext.

Unlike other actions, ReEncrypt is authorized twice - once as ReEncryptFrom on the source key and once as ReEncryptTo on the destination key. We therefore recommend that you include the "action":"kms:ReEncrypt*" statement in your key policies to permit re-encryption from or to the key. The statement is included automatically when you authorize use of the key through the console but must be included manually when you set a policy by using the PutKeyPolicy function.

retire_grant(client, input, options \\ [])
Retires a grant. You can retire a grant when you're done using it to clean up. You should revoke a grant when you intend to actively deny operations that depend on it. The following are permitted to call this API:
  • The account that created the grant
  • The RetiringPrincipal, if present
  • The GranteePrincipal, if RetireGrant is a grantee operation

The grant to retire must be identified by its grant token or by a combination of the key ARN and the grant ID. A grant token is a unique variable-length base64-encoded string. A grant ID is a 64 character unique identifier of a grant. Both are returned by the CreateGrant function.

revoke_grant(client, input, options \\ [])

Revokes a grant. You can revoke a grant to actively deny operations that depend on it.

update_alias(client, input, options \\ [])

Updates an alias to associate it with a different key.

An alias name can contain only alphanumeric characters, forward slashes (/), underscores (_), and dashes (-). An alias must start with the word "alias" followed by a forward slash (alias/). An alias that begins with "aws" after the forward slash (alias/aws...) is reserved by Amazon Web Services (AWS).

An alias is not a property of a key. Therefore, an alias can be associated with and disassociated from an existing key without changing the properties of the key.

Note that you cannot create or update an alias that represents a key in another account.

update_key_description(client, input, options \\ [])

Updates the description of a key.