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.
kms_generate_data_key(KeyId, EncryptionContext, NumberOfBytes, KeySpec, GrantTokens)
[required] 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
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.
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.
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 length of the data key. Use
A list of grant tokens.
For more information, see Grant Tokens in the AWS Key Management Service Developer Guide.
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
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
field of the response, and the encrypted copy of the data key in the
We recommend that you use the following pattern to encrypt data locally in your application:
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
Store the encrypted data key (returned in the
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
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.
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# 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 customer # master key (CMK). svc$generate_data_key( KeyId = "alias/ExampleAlias", KeySpec = "AES_256" )
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