SFTPGo stores sensitive data such as Cloud account credentials or passphrases to derive per-object encryption keys. These data are stored as ciphertext and only loaded to RAM in plaintext when needed.
## Supported Services for encryption and decryption
The `secrets` section of the `kms` configuration allows to configure how to encrypt and decrypt sensitive data. The following configuration parameters are available:
-`url` defines the URI to the KMS service
-`master_key_path` defines the absolute path to a file containing the master encryption key. This could be, for example, a docker secrets or a file protected with filesystem level permissions.
If the `url` is empty SFTPGo uses local encryption for keeping secrets. Internally, it uses the [NaCl secret box](https://pkg.go.dev/golang.org/x/crypto/nacl/secretbox) algorithm to perform encryption and authentication.
We first generate a random key, then the per-object encryption key is derived from this random key in the following way:
1. a master key is provided: the encryption key is derived using the HMAC-based Extract-and-Expand Key Derivation Function (HKDF) as defined in [RFC 5869](http://tools.ietf.org/html/rfc5869)
2. no master key is provided: the encryption key is derived as simple hash of the random key. This is the default configuration.
For compatibility with SFTPGo versions 1.2.x and before we also support encryption based on `AES-256-GCM`. The data encrypted with this algorithm will never use the master key to keep backward compatibility.
- If you set a master key you will be unable to decrypt the data without this key and the SFTPGo users that need the data as plain text will be unable to login.
- You can start using the local provider and then switch to an external one but you can't switch between external providers and still be able to decrypt the data encrypted using the previous provider.
