Modification Application of Key Metrics 13x13 Cryptographic Algorithm Playfair Cipher and Combination with Linear Feedback Shift Register (LFSR) on Data Security Based on Mobile Android

Playfair cipher is a classic encryption method that is difficult to manually manipulate but apart from the advantages found in plyafair cipher there are also many shortcomings, can be solved by using the information frequency of occurrence bigram, can not enter lowercase letters, numbers and special characters when encrypting This research modifies the key matrix of playfair cryptography algorithms and combines with the Linear Feedback Shift Register (LFSR) algorithm, by changing the size of the 13x13 key matrix the playfair cipher is able to insert characters as many as 196 characters consisting of capital letters, lowercase letters. The result of calculation with avalanche effect method got average value 43,59% at playfair cipher done by modification of matrix key 13x13 and combined with LFSR generator, 2,15% at playfair cipher 10x10 matrix key without merged with LFSR and 34,41% at playfair classic 5x5. That the playfair cipher that has been modified and combined with the LFSR generator is stronger than the previous playfair cipher. The result of time complexity testing has fast encryption and decryption.