How Amazon File Cache uses AWS KMS - Amazon File Cache
Amazon File Cache key policies for AWS KMS

How Amazon File Cache uses AWS KMS

Amazon File Cache integrates with AWS Key Management Service (AWS KMS) for key management for encrypting data at rest. File Cache uses AWS KMS keys to encrypt your cache in the following way:

  • Encrypting data at rest – Amazon File Cache encrypts data automatically before it is written to the cache, and automatically decrypts data as it is read. Data is encrypted using an XTS-AES-256 block cipher. You choose the KMS key that's used to encrypt and decrypt data, either the AWS managed key for Amazon File Cache, aws/fsx, or a customer managed key. You can enable, disable, or revoke grants on this KMS key. This KMS key can be one of the two following types:

    • AWS managed key for Amazon File Cache – This is the default KMS key, aws/fsx. You're not charged to create and store a KMS key, but there are usage charges. For more information, see AWS Key Management Service pricing.

    • Customer managed key – This is the most flexible KMS key to use, because you can configure its key policies and grants for multiple users or services. For more information on creating customer managed keys, see Creating keys in the AWS Key Management Service Developer Guide.

      If you use a customer managed key as your KMS key for file data encryption and decryption, you can enable key rotation. When you enable key rotation, AWS KMS automatically rotates your key once per year. Additionally, with a customer managed key, you can choose when to disable, re-enable, delete, or revoke access to your customer managed key at any time.

Important

Amazon File Cache accepts only symmetric encryption KMS keys. You can't use asymmetric KMS keys with Amazon File Cache.

Amazon File Cache key policies for AWS KMS

Key policies are the primary way to control access to KMS keys. For more information on key policies, see Using key policies in AWS KMS in the AWS Key Management Service Developer Guide. The following list describes all the AWS KMS–related permissions supported by Amazon File Cache for encrypted at rest caches:

  • kms:Encrypt – (Optional) Encrypts plaintext into ciphertext. This permission is included in the default key policy.

  • kms:Decrypt – (Required) Decrypts ciphertext. Ciphertext is plaintext that has been previously encrypted. This permission is included in the default key policy.

  • kms:ReEncrypt – (Optional) Encrypts data on the server side with a new KMS key, without exposing the plaintext of the data on the client side. The data is first decrypted and then re-encrypted. This permission is included in the default key policy.

  • kms:GenerateDataKeyWithoutPlaintext – (Required) Returns a data encryption key encrypted under a KMS key. This permission is included in the default key policy under kms:GenerateDataKey*.

  • kms:CreateGrant – (Required) Adds a grant to a key to specify who can use the key and under what conditions. Grants are alternate permission mechanisms to key policies. For more information on grants, see Using grants in the AWS Key Management Service Developer Guide. This permission is included in the default key policy.

  • kms:DescribeKey – (Required) Provides detailed information about the specified KMS key. This permission is included in the default key policy.

  • kms:ListAliases – (Optional) Lists all of the key aliases in the account. When you use the console to create an encrypted cache, this permission populates the list to select the KMS key. We recommend using this permission to provide the best user experience. This permission is included in the default key policy.