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/** @mainpage SafeChat

    SafeChat runs on:
    https://safechat.ch

    SafeChat development is on:
    https://dev.marc.waeckerlin.org/redmine/projects/safechat

    Implementation Details: @ref security, @ref api, @ref protocol,
    @ref database

    SafeChat is a chat program designed to protect your privacy. It is
    designed to be:
    
    -# extremely easy to use
       -# zero installation
       -# simple registration, within seconds
       -# web 2.0 - works in any modern browser
       -# user does not have to care about keys, security, encryption
    -# all cool features
       -# pseudonym accounts, no phone number, no email,nothing required
       -# send images and other attachments
       -# build groups
       -# no need to be online, receive messages on next login
       -# central user directory
    -# absolutely secure
       -# tap-proof
       -# no metadata available
         -# all messages are sent to all users, only the authorized users can decrypt it
       -# server can be untrusted
         -# thin server, rich client
           -# all encryption is done in the client
           -# server only stores minimal user data (name, public key) and encrypted messages
           -# no access to plain data, not even through server confiscation
       -# double secured internet transport
         -# messages are encrypted for the recipents only
         -# server connection is SSL secured in addition
       -# private data fully in the user's hand
         -# password is stored in the user's brain only
         -# private key is password encrypted
         -# private key is stored in the user's local machine only
       -# two factor security, access needs two tokens
         -# the password in the user's brain
         -# the private key in the user's browser memory
    -# fully open source

    @section why Why I Created SafeChat

    The Swiss parliament has decided to increase the power of police
    (BÜPF: Bundesgesetz zur Überwachung des Post- und
    Fernmeldeverkehrs) and secret service (NDG:
    Nachrichtendienstgesetz). This increases global enforced data
    preservation without any suspicion. This even allows the police to
    run a trojan in computers of suspicious persons.

    That was the point, when I started to think about secure
    communication that defeats these attacks against our
    privacy. Noone should be able to read what's not for his eyes,
    even if he controls the server. There should be no metadata,
    i.e. no one should know, who is communicating to each other.

    There are secure means of communication, i.e. Jabber/OTR and
    PGP-Mail (but with unprotected metadata). But these are too
    complicated for the avarage user. He has to take care about keys
    and their distribution. In some chat programs, there is no offline
    message store, so you can only send a message, if the receiver is
    online. Some chat programs require to identify you, they ask your
    phone number and some even steal your address book
    (i.e. WhatsApp). Not here! Use any pseudonym. No special knowledge
    needed. User is guided as much as possible, the interface is as
    simple as possible. Data is only collected, if it is necessary.

    So I present here the safe chat program for dummies

    @page security Password and Secrets Concept

    Neither the password nor the private key are sent to the
    server. They remain under the user's control and in the user's
    property. Only the user name and the public key are sent to the
    server.

     - The password is only kept in the browser's transient memory.
     - The private key is kept in encrypted form in the browser's
       persistent local storage.
     - The public key is stored on server, so that other users can
       lookup for a user's public key.

    There are two secret security tokens: The password, that is in the
    user's mind and the private key, which is in the user's device, in
    the local storage of his browser. Messages can only be sent or
    read with access to both security tokens.

    @page protocol SafeChat Protocol

    @tableofcontents

    @section newuser Create New User

    If no credentials exist in the browser's local storage, the
    browser asks the user for a user name and a password and creates a
    private key that is encrypted with the password.

    In the login(), the browser sends the user's name and public key
    to the server. The server creates a new user, if the user does not
    exist yet. Then the server returns, whether user name and public
    key match to what he has in his table.

    @msc
    user, browser, server;
    user -> browser [label="https://safechat.ch"];
    browser -> server [label="index.html"];
    browser <- server [label="safechat.js",URL="\ref safechat.js"];
    user <- browser [label="register new user"];
    user -> browser [label="username / password"];
    browser -> browser [label="create openpgp-public/private keys"];
    browser -> server [label="login.php(username, public-key)"];
    server -> server [label="if user name does not exist:\nstore username/public-key"];
    server -> browser [label="success"];
    @endmsc

*/