// ## SSE-S3
//
// SSE-S3 can use either a master key or a KMS as root-of-trust.
// The en/decryption slightly depens upon which root-of-trust is used.
//
// ### SSE-S3 and single master key
//
// The master key is used to derive unique object- and key-encryption-keys.
// SSE-S3 with a single master key works as SSE-C where the master key is
// used as the client-provided key.
//
//  1. Encrypt: