KMS

Rationale

AWS KMS  (Key Management Service) is the service we use for storing and using cryptographic keys. It allows us to have non-readable symmetric and asymmetric private keys hosted in the cloud .

The main reasons why we chose it over other alternatives are the following:

• It integrates  with other AWS  services like DynamoDB , EKS , S3 , EBS , among others.
• It uses a state-of-the-art approach for both encryption and decryption in which keys are never exposed. It accomplishes this by making users send the data they want to encrypt/decrypt and then returning it encrypted/decrypted. By doing so, keys never leave KMS . This approach greatly reduces the chances of key leakage, as plaintext keys can only be obtained via brute-force attacks .
• It complies with several  certifications from ISO  and CSA . Many of these certifications are focused on ensuring that the entity follows best practices regarding secure cloud-based environments and information security.
• It uses hardware security modules  validated under FIPS 140-2  so that no one can retrieve the existing keys. Such keys are never written to disk and only exist within volatile memory for the time needed to process requests.
• It provides a centralized key vault with complete API support  where you can store both AWS and customer-managed keys , rotate them , log and monitor them , set deletion waiting periods , etc.
• It supports a fully granular  authentication and access control model, where each key has a policy that specifies what actions users can execute. Additionally, when combined with AWS IAM , it allows us to specify permissions over general actions like creating keys.
• Keys and permissions can be written as code  using Terraform .
• It integrates with Sops , allowing us to use its keys for encrypting our versioned secrets.

Alternatives

• Google Cloud Key Management : It did not exist at the time we migrated to the cloud. It does not integrate with other AWS services, meaning that an entire platform migration would be required.
• Azure Key Vault : It did not exist at the time we migrated to the cloud. It does not integrate with other AWS services, meaning that an entire platform migration would be required.

Usage

We use AWS KMS  for

• DynamoDB encryption at rest ;
• S3 server-side encryption ;
• encrypting and decrypting  our Sops  secrets;
• encrypting and decrypting  our Kubernetes  workers EBS  disks;
• encrypting and decrypting our ERP  data EBS disk;
• encrypting and decrypting our Okta RADIUS  Agent EBS disk.

We do not use AWS KMS for

• Redshift  (the database is not encrypted at rest; this implementation is pending);
• CI Bastion  (it does not use EBS encrypted disks, since only the base operating system  and other minor dependencies are stored there);
• CI workers  (they do not use EBS encrypted disks, since only the base operating system is stored there);
• Batch workers  (they do not use EBS encrypted disks, since only the base operating system is stored there).