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AWS Key Management Service
API Reference (API Version 2014-11-01)

GenerateDataKey

Returns a data encryption key that you can use in your application to encrypt data locally.

You must specify the customer master key (CMK) under which to generate the data key. You must also specify the length of the data key using either the KeySpec or NumberOfBytes field. You must specify one field or the other, but not both. For common key lengths (128-bit and 256-bit symmetric keys), we recommend that you use KeySpec. To perform this operation on a CMK in a different AWS account, specify the key ARN or alias ARN in the value of the KeyId parameter.

This operation returns a plaintext copy of the data key in the Plaintext field of the response, and an encrypted copy of the data key in the CiphertextBlob field. The data key is encrypted under the CMK specified in the KeyId field of the request.

We recommend that you use the following pattern to encrypt data locally in your application:

  1. Use this operation (GenerateDataKey) to get a data encryption key.

  2. Use the plaintext data encryption key (returned in the Plaintext field of the response) to encrypt data locally, then erase the plaintext data key from memory.

  3. Store the encrypted data key (returned in the CiphertextBlob field of the response) alongside the locally encrypted data.

To decrypt data locally:

  1. Use the Decrypt operation to decrypt the encrypted data key into a plaintext copy of the data key.

  2. Use the plaintext data key to decrypt data locally, then erase the plaintext data key from memory.

To return only an encrypted copy of the data key, use GenerateDataKeyWithoutPlaintext. To return a random byte string that is cryptographically secure, use GenerateRandom.

If you use the optional EncryptionContext field, you must store at least enough information to be able to reconstruct the full encryption context when you later send the ciphertext to the Decrypt operation. It is a good practice to choose an encryption context that you can reconstruct on the fly to better secure the ciphertext. For more information, see Encryption Context in the AWS Key Management Service Developer Guide.

Request Syntax

{
   "EncryptionContext": { 
      "string" : "string" 
   },
   "GrantTokens": [ "string" ],
   "KeyId": "string",
   "KeySpec": "string",
   "NumberOfBytes": number
}

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

The identifier of the CMK under which to generate and encrypt the data encryption 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

EncryptionContext

A set of key-value pairs that represents additional authenticated data.

For more information, see Encryption Context in the AWS Key Management Service Developer Guide.

Type: String to string map

Required: No

GrantTokens

A list of grant tokens.

For more information, see Grant Tokens 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

KeySpec

The length of the data encryption key. Use AES_128 to generate a 128-bit symmetric key, or AES_256 to generate a 256-bit symmetric key.

Type: String

Valid Values: AES_256 | AES_128

Required: No

NumberOfBytes

The length of the data encryption key in bytes. For example, use the value 64 to generate a 512-bit data key (64 bytes is 512 bits). For common key lengths (128-bit and 256-bit symmetric keys), we recommend that you use the KeySpec field instead of this one.

Type: Integer

Valid Range: Minimum value of 1. Maximum value of 1024.

Required: No

Response Syntax

{
   "CiphertextBlob": blob,
   "KeyId": "string",
   "Plaintext": blob
}

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.

CiphertextBlob

The encrypted data encryption key. When you use the HTTP API or the AWS CLI, the value is Base64-encoded. Otherwise, it is not encoded.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 6144.

KeyId

The identifier of the CMK under which the data encryption key was generated and encrypted.

Type: String

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

Plaintext

The data encryption key. When you use the HTTP API or the AWS CLI, the value is Base64-encoded. Otherwise, it is not encoded. Use this data key for local encryption and decryption, then remove it from memory as soon as possible.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 4096.

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

InvalidGrantTokenException

The request was rejected because the specified grant token is not valid.

HTTP Status Code: 400

InvalidKeyUsageException

The request was rejected because the specified KeySpec value is not valid.

HTTP Status Code: 400

KeyUnavailableException

The request was rejected because the specified CMK was not available. The request can be retried.

HTTP Status Code: 500

KMSInternalException

The request was rejected because an internal exception occurred. The request can be retried.

HTTP Status Code: 400

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

Examples

The following examples are formatted for legibility.

Example Request

Copy
POST / HTTP/1.1 Host: kms.us-east-2.amazonaws.com Content-Length: 50 X-Amz-Target: TrentService.GenerateDataKey X-Amz-Date: 20161112T000940Z Content-Type: application/x-amz-json-1.1 Authorization: AWS4-HMAC-SHA256\ Credential=AKIAI44QH8DHBEXAMPLE/20161112/us-east-2/kms/aws4_request,\ SignedHeaders=content-type;host;x-amz-date;x-amz-target,\ Signature=815ac4ccbb5c53b8ca015f979704c7953bb0068bf53f4e0b7c6886ed5b0a8fe4 { "KeyId": "alias/ExampleAlias", "KeySpec": "AES_256" }

Example Response

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HTTP/1.1 200 OK Server: Server Date: Sat, 12 Nov 2016 00:09:40 GMT Content-Type: application/x-amz-json-1.1 Content-Length: 390 Connection: keep-alive x-amzn-RequestId: 4e6fc242-a86c-11e6-aff0-8333261e2fbd { "CiphertextBlob": "AQEDAHjRYf5WytIc0C857tFSnBaPn2F8DgfmThbJlGfR8P3WlwAAAH4wfAYJKoZIhvcNAQcGoG8wbQIBADBoBgkqhkiG9w0BBwEwHgYJYIZIAWUDBAEuMBEEDEFogLqPWZconQhwHAIBEIA7d9AC7GeJJM34njQvg4Wf1d5sw0NIo1MrBqZa+YdhV8MrkBQPeac0ReRVNDt9qleAt+SHgIRF8P0H+7U=", "KeyId": "arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab", "Plaintext": "VdzKNHGzUAzJeRBVY+uUmofUGGiDzyB3+i9fVkh3piw=" }

See Also

For more information about using this API in one of the language-specific AWS SDKs, see the following: