Secret key agreement based on noisy channel connecting parties and on public discussion has been considered in 1-4 for asymptotic case. Extension of the information-theoretically secure key sharing concept to non- asymptotic case was given in [5]. In the last paper several channel transform protocols (corresponding to different algorithms of public discussion) were presented. Unfortunately the efficiency of these protocols was very low in comparison with asymptotic key capacity found in [1]. The reason of this was that these protocols do not use a redundancy efficiently. One of the considered protocols (the socalled advantage to the main channel primitive) exploits a repetition of binary symbols only. It may be much better to use linear error detecting codes, that is just a subject of consideration in the current paper. We regain the main formulas to compute Renyi entropy which is necessary to bound the information about the final key leaking to an eavesdropper after execution of such modificated protocol. The use of this protocol causes an increase in the key-rate by several times, that is very important in practical implementations of key sharing procedures.