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

GenerateDataKey

Generates a unique symmetric data key. This operation returns a plaintext copy of the data key and a copy that is encrypted under a customer master key (CMK) that you specify. You can use the plaintext key to encrypt your data outside of AWS KMS and store the encrypted data key with the encrypted data.

GenerateDataKey returns a unique data key for each request. The bytes in the key are not related to the caller or CMK that is used to encrypt the data key.

To generate a data key, specify the symmetric CMK that will be used to encrypt the data key. You cannot use an asymmetric CMK to generate data keys.

You must also specify the length of the data key. Use either the KeySpec or NumberOfBytes parameters (but not both). For 128-bit and 256-bit data keys, use the KeySpec parameter.

If the operation succeeds, the plaintext copy of the data key is in the Plaintext field of the response, and the encrypted copy of the data key in the CiphertextBlob field.

To get only an encrypted copy of the data key, use GenerateDataKeyWithoutPlaintext. To generate an asymmetric data key pair, use the GenerateDataKeyPair or GenerateDataKeyPairWithoutPlaintext operation. To get a cryptographically secure random byte string, use GenerateRandom.

You can use the optional encryption context to add additional security to the encryption operation. If you specify an EncryptionContext, you must specify the same encryption context (a case-sensitive exact match) when decrypting the encrypted data key. Otherwise, the request to decrypt fails with an InvalidCiphertextException. For more information, see Encryption Context in the AWS Key Management Service Developer Guide.

The CMK that you use for this operation must be in a compatible key state. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide.

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

  1. Use the GenerateDataKey operation to get a data encryption key.

  2. Use the plaintext data 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. The operation returns 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.

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

Identifies the symmetric CMK that encrypts the data 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

Specifies the encryption context that will be used when encrypting the data key.

An encryption context is a collection of non-secret key-value pairs that represents additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is optional when encrypting with a symmetric CMK, but it is highly recommended.

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

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

You must specify either the KeySpec or the NumberOfBytes parameter (but not both) in every GenerateDataKey request.

Type: String

Valid Values: AES_256 | AES_128

Required: No

NumberOfBytes

Specifies the length of the data key in bytes. For example, use the value 64 to generate a 512-bit data key (64 bytes is 512 bits). For 128-bit (16-byte) and 256-bit (32-byte) data keys, use the KeySpec parameter.

You must specify either the KeySpec or the NumberOfBytes parameter (but not both) in every GenerateDataKey request.

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 copy of the data key. 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 6144.

KeyId

The identifier of the CMK that encrypted the data key.

Type: String

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

Plaintext

The plaintext data key. When you use the HTTP API or the AWS CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded. Use this data key to encrypt your data outside of KMS. 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 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 be ENCRYPT_DECRYPT. For signing and verifying, the KeyUsage must be SIGN_VERIFY. To find the KeyUsage 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

Examples

The following examples are formatted for legibility.

Example Request

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

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: