Requests submitted to a computer system are evaluated for compliance with policy to ensure data security. Plaintext and associated data are used as inputs into a cipher to produce ciphertext. Whether a result of decrypting the ciphertext can be provided in response to a request is determined based at least in part on evaluation of a policy that itself is based at least in part on the associated data. Other policies include automatic rotation of keys to prevent keys from being used in enough operations to enable cryptographic attacks intended to determine the keys.