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[ aws . kms ]

generate-data-key

Description

Generates a unique 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 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, you need to specify the customer master key (CMK) that will be used to encrypt the data key. You must also specify the length of the data key using either the KeySpec or NumberOfBytes field (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.

You will find the plaintext copy of the data key in the Plaintext field of the response, and the encrypted copy of the data key in the CiphertextBlob field.

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

  • Use the GenerateDataKey operation to get a data encryption key.
  • 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.
  • Store the encrypted data key (returned in the CiphertextBlob field of the response) alongside the locally encrypted data.

To decrypt data locally:

  • Use the Decrypt operation to decrypt the encrypted data key. The operation returns a plaintext copy of the data key.
  • Use the plaintext data key to decrypt data locally, then erase the plaintext data key from memory.

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

You can use the optional encryption context to add additional security to your encryption operation. When you specify an EncryptionContext in the GenerateDataKey operation, you must specify the same encryption context (a case-sensitive exact match) in your request to Decrypt the 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 result of this operation varies with the key state of the CMK. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide .

See also: AWS API Documentation

See 'aws help' for descriptions of global parameters.

Synopsis

  generate-data-key
--key-id <value>
[--encryption-context <value>]
[--number-of-bytes <value>]
[--key-spec <value>]
[--grant-tokens <value>]
[--cli-input-json <value>]
[--generate-cli-skeleton <value>]

Options

--key-id (string)

An identifier for the 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 .

--encryption-context (map)

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 .

Shorthand Syntax:

KeyName1=string,KeyName2=string

JSON Syntax:

{"string": "string"
  ...}

--number-of-bytes (integer)

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 common key lengths (128-bit and 256-bit symmetric keys), we recommend that you use the KeySpec field instead of this one.

--key-spec (string)

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.

Possible values:

  • AES_256
  • AES_128

--grant-tokens (list)

A list of grant tokens.

For more information, see Grant Tokens in the AWS Key Management Service Developer Guide .

Syntax:

"string" "string" ...

--cli-input-json (string) Performs service operation based on the JSON string provided. The JSON string follows the format provided by --generate-cli-skeleton. If other arguments are provided on the command line, the CLI values will override the JSON-provided values. It is not possible to pass arbitrary binary values using a JSON-provided value as the string will be taken literally.

--generate-cli-skeleton (string) Prints a JSON skeleton to standard output without sending an API request. If provided with no value or the value input, prints a sample input JSON that can be used as an argument for --cli-input-json. If provided with the value output, it validates the command inputs and returns a sample output JSON for that command.

See 'aws help' for descriptions of global parameters.

Output

CiphertextBlob -> (blob)

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 encoded.

Plaintext -> (blob)

The plaintext data 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 to encrypt your data outside of KMS. Then, remove it from memory as soon as possible.

KeyId -> (string)

The identifier of the CMK that encrypted the data key.