The earliest  frequently known use of a substitution
technique is one in which each letter of plaintext is
replaced with the letter standing three places further down
the alphabet. When we use the alphabet ${\cal P} =
\{\sqcup,a,b,c,\dots, w,x,y,z,\}$, and apply this method of
ciphering to the plaintext

\centerline{\bf what kama sutra did suggested...}
\vskip0.25cm
\noindent we get the title of this article...  In these few pages
we would like to introduce a very attractive branch of
mathematics as well as of computer science called cryptology.
Our aim is to introduce to a freshman in the field some basic ideas
leading to the three methods of ciphering: classical, block and asymmetric
ciphers.

