Support for E2E encryption

[DeerMaximum]

This PR contains a proof of concept for E2E support.
For this, a session store must be created and the E2E room keys imported.
In order for the messages to be displayed as secure, the session must be verified by all recipients.

Related to #32

Note

The decision whether to activate encryption must be passed to the program at the first start.
Changing (de)activation of the encryption afterwards is not supported.

Breaking changes

• Login via access token is no longer possible.

Program modes

The program can be executed in two modes, run and verify. In run mode the program is executed as usual and a webhook is provided.
In verify mode, the session can be verified interactively via emojis to classify the messages as trustworthy.

Important

In verification mode, the matrix id must be specified completely, otherwise the verification will fail.
Eg: @test:matrix.org

New command-line parameters

--mode

This parameter is used to switch between verification and normal program.
It accepts two options run and verify.

Default: run

--storage

This parameter specifies the path where the session storage is located.

Default: ./storage

--key-password

This parameter contains the password for the E2E room keys.

--encryption

This parameter specifies whether encryption is enabled.

Folder structure of the session storage

├── session-storage
    ├── element-keys.txt
    ├── data.json

Files

In this folder, apart from the ones listed below, matrix-nio creates additional files that allow you to send encrypted messages.

element-keys.txt

This file contains the room keys exported by Matrix. Here a tutorial on how to export these keys.

data.json

This file contains the access token, the device ID and the status whether encryption has been enabled.