:doc:`KMS <../../kms>` / Client / generate_data_key

*****************
generate_data_key
*****************



.. py:method:: KMS.Client.generate_data_key(**kwargs)

  

  Returns a unique symmetric data key for use outside of KMS. This operation returns a plaintext copy of the data key and a copy that is encrypted under a symmetric encryption KMS key that you specify. The bytes in the plaintext key are random; they are not related to the caller or the KMS key. You can use the plaintext key to encrypt your data outside of KMS and store the encrypted data key with the encrypted data.

   

  To generate a data key, specify the symmetric encryption KMS key that will be used to encrypt the data key. You cannot use an asymmetric KMS key to encrypt data keys. To get the type of your KMS key, use the  DescribeKey operation.

   

  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.

   

  To generate a 128-bit SM4 data key (China Regions only), specify a ``KeySpec`` value of ``AES_128`` or a ``NumberOfBytes`` value of ``16``. The symmetric encryption key used in China Regions to encrypt your data key is an SM4 encryption key.

   

  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 an 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 <https://docs.aws.amazon.com/kms/latest/developerguide/encrypt_context.html>`__ in the *Key Management Service Developer Guide*.

   

  ``GenerateDataKey`` also supports `Amazon Web Services Nitro Enclaves <https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/nitro-enclave.html>`__, which provide an isolated compute environment in Amazon EC2. To call ``GenerateDataKey`` for an Amazon Web Services Nitro enclave or NitroTPM, use the `Amazon Web Services Nitro Enclaves SDK <https://docs.aws.amazon.com/enclaves/latest/user/developing-applications.html#sdk>`__ or any Amazon Web Services SDK. Use the ``Recipient`` parameter to provide the attestation document for the attested environment. ``GenerateDataKey`` returns a copy of the data key encrypted under the specified KMS key, as usual. But instead of a plaintext copy of the data key, the response includes a copy of the data key encrypted under the public key from the attestation document ( ``CiphertextForRecipient``). For information about the interaction between KMS and Amazon Web Services Nitro Enclaves or Amazon Web Services NitroTPM, see `Cryptographic attestation support in KMS <https://docs.aws.amazon.com/kms/latest/developerguide/cryptographic-attestation.html>`__ in the *Key Management Service Developer Guide*.

   

  The KMS key that you use for this operation must be in a compatible key state. For details, see `Key states of KMS keys <https://docs.aws.amazon.com/kms/latest/developerguide/key-state.html>`__ in the *Key Management Service Developer Guide*.

   

  **How to use your data key**

   

  We recommend that you use the following pattern to encrypt data locally in your application. You can write your own code or use a client-side encryption library, such as the `Amazon Web Services Encryption SDK <https://docs.aws.amazon.com/encryption-sdk/latest/developer-guide/>`__, the `Amazon DynamoDB Encryption Client <https://docs.aws.amazon.com/dynamodb-encryption-client/latest/devguide/>`__, or `Amazon S3 client-side encryption <https://docs.aws.amazon.com/AmazonS3/latest/dev/UsingClientSideEncryption.html>`__ to do these tasks for you.

   

  To encrypt data outside of KMS:

   

   
  * Use the ``GenerateDataKey`` operation to get a data key.
   
  * Use the plaintext data key (in the ``Plaintext`` field of the response) to encrypt your data outside of KMS. Then erase the plaintext data key from memory.
   
  * Store the encrypted data key (in the ``CiphertextBlob`` field of the response) with the encrypted data.
   

   

  To decrypt data outside of KMS:

   

   
  * 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 outside of KMS, then erase the plaintext data key from memory.
   

   

  **Cross-account use**: Yes. To perform this operation with a KMS key in a different Amazon Web Services account, specify the key ARN or alias ARN in the value of the ``KeyId`` parameter.

   

  **Required permissions**: `kms\:GenerateDataKey <https://docs.aws.amazon.com/kms/latest/developerguide/kms-api-permissions-reference.html>`__ (key policy)

   

  **Related operations:**

   

  
  *  Decrypt
   
  *  Encrypt
   
  *  GenerateDataKeyPair
   
  *  GenerateDataKeyPairWithoutPlaintext
   
  *  GenerateDataKeyWithoutPlaintext
  

   

  **Eventual consistency**: The KMS API follows an eventual consistency model. For more information, see `KMS eventual consistency <https://docs.aws.amazon.com/kms/latest/developerguide/accessing-kms.html#programming-eventual-consistency>`__.

  

  See also: `AWS API Documentation <https://docs.aws.amazon.com/goto/WebAPI/kms-2014-11-01/GenerateDataKey>`_  


  **Request Syntax**
  ::

    response = client.generate_data_key(
        KeyId='string',
        EncryptionContext={
            'string': 'string'
        },
        NumberOfBytes=123,
        KeySpec='AES_256'|'AES_128',
        GrantTokens=[
            'string',
        ],
        Recipient={
            'KeyEncryptionAlgorithm': 'RSAES_OAEP_SHA_256',
            'AttestationDocument': b'bytes'
        },
        DryRun=True|False
    )
    
  :type KeyId: string
  :param KeyId: **[REQUIRED]** 

    Specifies the symmetric encryption KMS key that encrypts the data key. You cannot specify an asymmetric KMS key or a KMS key in a custom key store. To get the type and origin of your KMS key, use the  DescribeKey operation.

     

    To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with ``"alias/"``. To specify a KMS key in a different Amazon Web Services 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 KMS key, use  ListKeys or  DescribeKey. To get the alias name and alias ARN, use  ListAliases.

    

  
  :type EncryptionContext: dict
  :param EncryptionContext: 

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

     

    .. warning::

       

      Do not include confidential or sensitive information in this field. This field may be displayed in plaintext in CloudTrail logs and other output.

       

     

    An *encryption context* is a collection of non-secret key-value pairs that represent 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 supported only on operations with symmetric encryption KMS keys. On operations with symmetric encryption KMS keys, an encryption context is optional, but it is strongly recommended.

     

    For more information, see `Encryption context <https://docs.aws.amazon.com/kms/latest/developerguide/encrypt_context.html>`__ in the *Key Management Service Developer Guide*.

    

  
    - *(string) --* 

    
      - *(string) --* 

      


  :type NumberOfBytes: integer
  :param 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 KeySpec: string
  :param 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 GrantTokens: list
  :param GrantTokens: 

    A list of grant tokens.

     

    Use a grant token when your permission to call this operation comes from a new grant that has not yet achieved *eventual consistency*. For more information, see `Grant token <https://docs.aws.amazon.com/kms/latest/developerguide/grants.html#grant_token>`__ and `Using a grant token <https://docs.aws.amazon.com/kms/latest/developerguide/using-grant-token.html>`__ in the *Key Management Service Developer Guide*.

    

  
    - *(string) --* 

    

  :type Recipient: dict
  :param Recipient: 

    A signed `attestation document <https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/nitro-enclave-how.html#term-attestdoc>`__ from an Amazon Web Services Nitro enclave or NitroTPM, and the encryption algorithm to use with the public key in the attestation document. The only valid encryption algorithm is ``RSAES_OAEP_SHA_256``.

     

    This parameter supports the `Amazon Web Services Nitro Enclaves SDK <https://docs.aws.amazon.com/enclaves/latest/user/developing-applications.html#sdk>`__ or any Amazon Web Services SDK for Amazon Web Services Nitro Enclaves. It supports any Amazon Web Services SDK for Amazon Web Services NitroTPM.

     

    When you use this parameter, instead of returning the plaintext data key, KMS encrypts the plaintext data key under the public key in the attestation document, and returns the resulting ciphertext in the ``CiphertextForRecipient`` field in the response. This ciphertext can be decrypted only with the private key in the enclave. The ``CiphertextBlob`` field in the response contains a copy of the data key encrypted under the KMS key specified by the ``KeyId`` parameter. The ``Plaintext`` field in the response is null or empty.

     

    For information about the interaction between KMS and Amazon Web Services Nitro Enclaves or Amazon Web Services NitroTPM, see `Cryptographic attestation support in KMS <https://docs.aws.amazon.com/kms/latest/developerguide/cryptographic-attestation.html>`__ in the *Key Management Service Developer Guide*.

    

  
    - **KeyEncryptionAlgorithm** *(string) --* 

      The encryption algorithm that KMS should use with the public key for an Amazon Web Services Nitro Enclave or NitroTPM to encrypt plaintext values for the response. The only valid value is ``RSAES_OAEP_SHA_256``.

      

    
    - **AttestationDocument** *(bytes) --* 

      The attestation document for an Amazon Web Services Nitro Enclave or a NitroTPM. This document includes the enclave's public key.

      

    
  
  :type DryRun: boolean
  :param DryRun: 

    Checks if your request will succeed. ``DryRun`` is an optional parameter.

     

    To learn more about how to use this parameter, see `Testing your permissions <https://docs.aws.amazon.com/kms/latest/developerguide/testing-permissions.html>`__ in the *Key Management Service Developer Guide*.

    

  
  
  :rtype: dict
  :returns: 
    
    **Response Syntax**

    
    ::

      {
          'CiphertextBlob': b'bytes',
          'Plaintext': b'bytes',
          'KeyId': 'string',
          'CiphertextForRecipient': b'bytes',
          'KeyMaterialId': 'string'
      }
      
    **Response Structure**

    

    - *(dict) --* 
      

      - **CiphertextBlob** *(bytes) --* 

        The encrypted copy of the data key. When you use the HTTP API or the Amazon Web Services CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.

        
      

      - **Plaintext** *(bytes) --* 

        The plaintext data key. When you use the HTTP API or the Amazon Web Services 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.

         

        If the response includes the ``CiphertextForRecipient`` field, the ``Plaintext`` field is null or empty.

        
      

      - **KeyId** *(string) --* 

        The Amazon Resource Name ( `key ARN <https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#key-id-key-ARN>`__) of the KMS key that encrypted the data key.

        
      

      - **CiphertextForRecipient** *(bytes) --* 

        The plaintext data key encrypted with the public key from the attestation document. This ciphertext can be decrypted only by using a private key from the attested environment.

         

        This field is included in the response only when the ``Recipient`` parameter in the request includes a valid attestation document from an Amazon Web Services Nitro enclave or NitroTPM. For information about the interaction between KMS and Amazon Web Services Nitro Enclaves or Amazon Web Services NitroTPM, see `Cryptographic attestation support in KMS <https://docs.aws.amazon.com/kms/latest/developerguide/cryptographic-attestation.html>`__ in the *Key Management Service Developer Guide*.

        
      

      - **KeyMaterialId** *(string) --* 

        The identifier of the key material used to encrypt the data key. This field is omitted if the request includes the ``Recipient`` parameter.

        
  
  **Exceptions**
  
  *   :py:class:`KMS.Client.exceptions.NotFoundException`

  
  *   :py:class:`KMS.Client.exceptions.DisabledException`

  
  *   :py:class:`KMS.Client.exceptions.KeyUnavailableException`

  
  *   :py:class:`KMS.Client.exceptions.DependencyTimeoutException`

  
  *   :py:class:`KMS.Client.exceptions.InvalidKeyUsageException`

  
  *   :py:class:`KMS.Client.exceptions.InvalidGrantTokenException`

  
  *   :py:class:`KMS.Client.exceptions.KMSInternalException`

  
  *   :py:class:`KMS.Client.exceptions.KMSInvalidStateException`

  
  *   :py:class:`KMS.Client.exceptions.DryRunOperationException`

  

  **Examples**

  The following example generates a 256-bit symmetric data encryption key (data key) in two formats. One is the unencrypted (plainext) data key, and the other is the data key encrypted with the specified KMS key.
  ::

    response = client.generate_data_key(
        # The identifier of the KMS key to use to encrypt the data key. You can use the key ID or Amazon Resource Name (ARN) of the KMS key, or the name or ARN of an alias that refers to the KMS key.
        KeyId='alias/ExampleAlias',
        # Specifies the type of data key to return.
        KeySpec='AES_256',
    )
    
    print(response)

  
  Expected Output:
  ::

    {
        # The encrypted data key.
        'CiphertextBlob': '<binary data>',
        # The ARN of the KMS key that was used to encrypt the data key.
        'KeyId': 'arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab',
        # The unencrypted (plaintext) data key.
        'Plaintext': '<binary data>',
        'ResponseMetadata': {
            '...': '...',
        },
    }

  