4.1 Classic encryption techniquesEncryption was introduced for sending secret messages. With the development of cryptography, few techniques have been standardized. They are:Substitution cipherTransposition cipherProduct cipher4.1.1 Substitution cipherReplacing each plaintext element into another element is called substitution cipher.The most famous is the Ceaser cipher invented by Julius Caesar. Each letter is replaced by the letter three positions lower in the alphabet. (Lai, 2010)Plan text: cessar encryption techniqueAlphabet: abcdefghijklmnopqrstu vwxy zCipher albhabet: defghijklmnopqrstuvwx yzab cChiper text: fhdvhu flskhu whfkqltxhUsing Ceaser Cipher, it was easily predicted to have only a small portion of the ciphertext. So Caesar had to protect the ciphertext as well. It has been kept simple so anyone can quickly send a message in no time. By making ciphertext more difficult, the algorithm had to be carried with the messenger for decryption, so there was a big risk in missing a message which would cause all ciphertext to be decrypted by enemies. So Ceaser made his algorithm easy and simple. (Pfleeger & Pfleeger, 2007)4.1.2 Transposition Cipher Rearrangement of the order of elements in plaintext is known as transposition cipher. (Lai, 2010) Columnar transposition is a way of arranging plaintext characters into columns. Here is an example of pictorial text that has been placed in 4 columns. When creating 4 columns blank was created by blank. When reading, it was read by columns, so it is difficult to predict while the number of columns is unknown. Also, to make it more difficult, we have changed the way to read instead of reading from first to... middle of paper......0: Encryption with generated keysA user will select a text file to encrypt. To complete the user will need to select the key pair, the user's private key and the recipient's public key that will decode this message. Figures 21, 22 and 23 are evidence of the process. Figure 21: Encryption process Figure 22: Test text file used for encryption (recipient who will decrypt and sender's audience who encrypted the message). The encrypted message will also be located by the user. After providing a location to save the decrypted text, the process will create the file in that location with the name Decipher_text.txt as mentioned above. Figure 24: Decryption process Figure 25: Decrypted text file