Nowadays, there is a trend of securing all the communication through the public internet network by means of an encryption. However, there are plenty of cases where this automatic encryption is not available or its use is not desirable for many different reasons. This article is focused on the authentication passwords’ protection being sent through the public network of the internet without any other securing elements. An algorithm presented makes the secure authentication for applications communicating with a server possible. An algorithm’s principle is based on the similar way of securing passwords as it is the securing user passwords in databases. A main innovation and a condition of the protection consist in the server’s ability to identify already used salts and to require their uniqueness in incoming messages. Thanks to its unique salts, the server either completely excludes sending passwords or their simply hashes, however, herewith excludes receiving kinds of “man in the middle” messages counterfeited by an attacker, namely including options of repeated sending messages and demand captured by him before. A programmer implementation of the mentioned procedure is very easy and in addition to it can be applied on a multiple platform. A first-rate user password being used, it is going to provide an authenticationsafe enough for a client’s application of the communication with the server, even when no other securing technologies are used. At the same time, a communication deceleration of every particular connection due this principle is reasonably low.

authentication, communication, salt, hash, man in the middle.