Use this option if you can securely distribute the AES key to each client.\
It is somewhat similar to [SSL](./SSL.md) mode with a self-signed certificate.

Xpra's AES [encryption](./Encryption.md) layer uses the [python cryptography](https://pypi.python.org/pypi/cryptography) library to encrypt the network packets with [AES-256 - Advanced Encryption Standard](http://en.wikipedia.org/wiki/Advanced_Encryption_Standard) in [CBC - Cipher Block Chaining](http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher-block_chaining_.28CBC.29), [GCM - Galois/Counter Mode](https://en.wikipedia.org/wiki/Galois/Counter_Mode), [CTR - Counter Mode](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Counter_(CTR)) or [CFB - Cipher_feedback](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher_feedback_(CFB)).

The encryption key can be stored in a keyfile or specified using the `keydata` socket option. If neither is present and an authentication module was used, the password will be used as key data.\
The key data is stretched using [PBKDF2](http://en.wikipedia.org/wiki/PBKDF2)(Password-Based Key Derivation Function 2).\
The salts used are generated using Python's [os.urandom()](https://docs.python.org/3/library/os.html#os.urandom) which is _suitable for cryptographic use_

Caveats:
* it is also possible to run in `AES-128` or `AES-192` mode but this is not recommended
* the HTML5 client currently does not support GCM mode: https://github.com/Xpra-org/xpra-html5/issues/94

For step by step instructions on setting up AES, expand:
<details>
  <summary>AES Usage Example</summary>

generate a key:
```
uuidgen > ./key.txt
```
start a server:
```
xpra start --start=xterm \
     --bind-tcp=0.0.0.0:10000,encryption=AES,keyfile=key.txt
```
* client:
```
xpra attach "tcp://localhost:10000/?encryption=AES&keyfile=./key.txt"
```

## Modes
AES encryption supports 3 different [modes of operation](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation): `CBC`, `GCM` ,`CFB` and `CTR`.

The client can specify the exact mode using: `encryption=AES-GCM`.

</details>

<details>
  <summary>Specifying the key data</summary>

## keydata
Instead of storing the encryption key in a file, it is also possible to inline the `keydata` value in the bind and attach strings:
* `keydata=0x...` for hexadecimal encoded keys
* `keydata=base64:...` for base64 encoded keys
* `keydata=...` for plain text keys

One major disadvantage is that the key data may be leaked in the process list.\
However, it may be easier in some cases to generate commands that do not require extra files to run.
This can also be used with `.xpra` session files, and those do not leak the data.
</details>

<details>
  <summary>Debugging</summary>

To verify that your client connection is using AES, look for `cipher=AES`:
```
xpra info | grep cipher=
```

To enable debugging, use the `-d crypto` [debug logging](../Usage/Logging.md) option.
</details>
