In transposition the positions of letters or words are changed based on the probabilities using 26 letters and 10 numbers. In transposition method both parties have to know the transposition formula like transposing forward three letters by making “A” to “D”, “B” to “E” and so on. As the name suggests the substation method is the replacement of a letter or a group of letters with another letter or group of letters, like reversing the alphabet, so the “A” becomes “Z”, “B” becomes “Y” and so on. Transposition is a change in the position of letters or words. Substitution is the replacement of a letter or group of letters with another letter or group of letters.