“ Add your company slogan ”

Playfair Cipher and Shift Cipher Kriptografi – 3rd Week

LOGO Aisyatul Karima, 2012 . Standar kompetensi . Pada akhir semester, mahasiswa menguasai pengetahuan, pengertian, & pemahaman tentang teknik-teknik kriptografi. Selain itu mahasiswa diharapkan mampu mengimplementasikan salah satu teknik kriptografi untuk mengamankan informasi yang akan dikirimkan melalui jaringan.

. Kompetensi dasar . Mahasiswa menguasai teknik playfair cipher . Mahasiswa menguasai teknik shift cipher Contents

1 Play fair Cipher Method

2 Shift Cipher Method Playfair Cipher Method

. Playfair cipher or Playfair square is symetric encryption technique that member of digraph substitution technique. . This technique encrypt digraph or pair of alphabet . Based on the reason, this technique hard to encode compare with the simple substitution technique. Playfair Cipher Method

. This technique found by Charles Wheatstone on physics he is founder of wheatstone bridge on 1854. Charles Wheatstone . But, popularized by Lord Playfair.

Lord Playfair Playfair Cipher Method

. The process of playfair cipher : . The key composed by 25 letters that arranged in a square 5x5 by removing the letter J from alphabet.

S T A N D E R C H B K F G I L M O P Q U V W X Y Z ?????

. contoh kunci yang digunakan . Jumlah kemungkinan kunci dari sistem ini adalah : 25!=15.511.210.043.330.985.984.000.000 Playfair Cipher Method

. The keys on square expanded by adding the 6th column and the 6th row.

6th column = 1st column

S T A N D S E R C H B E K F G I L K M O P Q U M V W X Y Z V S T A N D 6th row = 1st row Playfair Cipher Method

. The plaintext that hidden must be arranged before encryption process :

• Change letter J with the letter I • Write the plaintext on pair of letters • There must be no same pair of letters, if there is the same pair of letter, insert Z in the middle. • If the amount of letter is odd, add the letter Z at the end Playfair Cipher Method

. Example : . plaintext GOOD BROOMS SWEEP CLEAN

. There is no letter J, so write the plaintext on letter pairs. GO OD BR OZ OM SZ SW EZ EP CL EA NZ

. Ciphertext = … ??? Playfair Cipher Method . The encryption algorithm :

. If there are two letters on the same key rows, then each letter changed by the letter on the right side.

. If there are two letters on the same key column, then each letter changed by the letter on the bottom side.

. If there are no two letter on the same row or the same column, then the 1st letter changed by the letter on row intersected by the 1st letter with the 2nd letter. The 2nd letter changed by the letter on the 4th vertex of rectangle that built from 3 letters that used so far. . plainteks GOOD BROOMS SWEEP CLEAN

. Cipherteks: FP UT EC UW PO DV TV BV CM BG CS DY Playfair Cipher Method . plaintext

UNIVERSITAS DIAN NUSWANTORO

FAKULTAS ILMU KOMPUTER

DUMUNING INGSUN ANGRAKSO NEGORO

SEMARANG JAWA TENGAH

TEKNIK INFORMATIKA

LAWANG SEWU KERAMAT Shift Cipher Method

. Based on history, the shift cipher was ever been used at the time of ancient roman on Julius Caesar period. . The method was very simple by moving each letters of plaintext. Shift Cipher Method

. For the example, if X is the plaintext on the form of number : . K is Key with 0 ≤ K ≤ 25 and . Y is ciphertext on the form of number . The encryption process given by function : eK(x) = (x + K) mod 26 . The decryption process given by function : dK(y) = (y – K) mod 26. Shift Cipher Method

. For the key K = 3, shift cipher often called by Caesar Cipher, . For the Key K = 13 often called by Rot-13 cipher. . Example : . Define the ciphertext of plaintext “saya” using K = 3 “…..” ??? Shift Cipher Method

. Contoh: . Shift Cipher with 13 movement :

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z M N O P Q R S T U V W X Y Z A B C D E F G H I J K L

. Plaintext :

MERWAN MINTA MAAF PADA MARWAN

. Ciphertext = …. ??? “ Add your company slogan ”

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