From the 26-letter alphabet of the English language the letters x and z are dropped and replaced by the combination ks and cs. The remaining 24 letters are taken in some order as elements of the symmetric group $S_4$. An algorithm is described for changing the clear words (of a plain text) into the hidden ones. To make such a cipher only one letter as a key needs to be memorized (the group $S_4$ being automatically constructed starting with $S_1$). The encryption and decryption of this cipher is described and the measure of security of the cipher is given. A worked out example is also given.