Project Omar Hesham Ahmed Ali A New Algorithm Combining Substitution Omar Nabil Youssef essam Transposition Cipher Techniques for Secure Karim Ahmed Communication Motivation The proposed Cipher Omar Hesham Techniques Ahmed Ali Encryption Omar Nabil Decryption Youssef essam Karim Ahmed Results Conclusions COMM1003:Information Theory Communications Engineering Department Information Engineering and Technology Faculty The German University in Cairo April 12th, 2018 1 / 24 Overview Project Omar Hesham Ahmed Ali 1 Motivation Omar Nabil Youssef essam Karim Ahmed 2 The proposed Cipher Techniques Motivation The proposed Cipher 3 Encryption Techniques Encryption 4 Decryption Decryption Results 5 Results Conclusions 6 Conclusions 2 / 24 Motivation Project Omar Hesham In today’s world of communication, the maintenance of the security, Ahmed Ali Omar Nabil confidentiality and integrity of the data is a big challenge. Youssef essam Cryptography is one such activity that ensures the secure transmission Karim Ahmed of data. Motivation It converts the data or message (plain text) into a non-readable form The proposed Cipher Techniques (cipher text) with the help of an algorithm and key which known to sender and receiver only. Encryption Decryption Results Conclusions 3 / 24 Motivation Project Omar Hesham The transmission of message or information is over an insecure channel as Ahmed Ali cryptography retain authentication, integrity and non repudiation Omar Nabil Youssef essam This message ‘Cipher Text’ is transmitted at receiver’s end where there the text is Karim Ahmed decrypted again to the original text using the same key and the decryption Motivation algorithm Also ‘Cipher Text’ is transmitted to the crypt analysts who decipher the text The proposed Cipher Techniques without any knowledge of key Encryption Therefore, the aim of cryptographers is to produce an intelligent cipher which is harder to depict and cracked by the cryptanalysts Decryption The algorithm must be efficient and easy enough to be understood by the parties Results involved in communication and can be used repeatedly using different key each Conclusions time 4 / 24 Motivation Project Related Works Omar Hesham Ahmed Ali Many such techniques have come into the picture till date such as: Ceaser cipher, Omar Nabil vernam cipher, vigenere cipher technique Youssef essam Karim Ahmed The use of modern avatar of Julius Caesar cipher technique to encrypt and decrypt the message into cipher text by choosing primitive root first and then using the Motivation encryption technique : 퐶푖 = (푀푖 + 퐾푖)푚표푑26 The proposed Cipher 푀푖 = (퐶푖 − 퐾푖)푚표푑26. Techniques And encryption technique : Bit level conversion of inconsistent block length characters for encryption Encryption A substitution technique which is being followed on block of characters with Decryption transposition Results Conclusions 5 / 24 Motivation Project The Aim Omar Hesham Ahmed Ali A new cipher technique which consists of three step process Omar Nabil Youssef essam which are substitution, transposition then substitution again. Karim Ahmed Using this technique, the plain text can be converted into the cipher text which is Motivation the combination of various symbols defined in a given table that in turn makes the plain text unpredictable. The proposed Cipher Techniques Encryption Decryption Results Conclusions 6 / 24 The proposed Cipher Techniques Project Omar Hesham Two cipher techniques were used in the paper Ahmed Ali Omar Nabil Substitution Cipher: A method in which units of the plain text are Youssef essam substituted or replaced by different characters Karim Ahmed Transposition Cipher: A method in which the position of characters of Motivation the plain text are shifted according to some format or algorithm The proposed Cipher Techniques Blending both techniques in a single algorithm have high chances of Encryption producing a secret encrypted message. Decryption Results Conclusions 7 / 24 The proposed Cipher Techniques Project Multiplication Cipher Omar Hesham Ahmed Ali Each character of a plain text is encrypted by multiplying it with a certain key Omar Nabil using the formula ((character*secret–key)mod26) Youssef essam Karim Ahmed The secret key is chosen carefully such that multiplying it with any character would yield a different character for each plaintext character. Motivation The key must not be 0 or 1. The proposed Cipher Techniques Decryption is done by multiplying each cipher text character by the inverse of the secret key to obtain the plain text character. Encryption As the integral value of ‘A’ is 0, it will always produce A in the cipher text. Decryption Results Conclusions 8 / 24 The proposed Cipher Techniques Project Multiplication Cipher Omar Hesham Ahmed Ali Some keys such as 3,5,7,9,11,19 are good keys for encryption because these keys Omar Nabil produce a distinct character for each alphabet Youssef essam Karim Ahmed The inverse of such keys are 9,21,15,3,19,11 respectively Motivation The proposed Cipher Techniques Encryption Decryption Results Conclusions 9 / 24 The proposed Cipher Techniques Project Rail Fence Cipher Omar Hesham Ahmed Ali Also known as the zigzag cipher due to the way in which it is encoded Omar Nabil Youssef essam The key is the number of lines used and the number of characters of the cipher Karim Ahmed text is the number of columns Motivation The plain text is first written downwards diagonally on successive rows, then moving up when one hits the bottom row. When one reaches the top row, the The proposed Cipher Techniques message is written downwards again until the whole plaintext is written. The message is then read off in rows Encryption Decryption Results Conclusions 10 / 24 Encryption Project Omar Hesham Our algorithm consists of three steps Ahmed Ali Omar Nabil Step 1: Substitution Youssef essam Karim Ahmed Step 2: Transposition Motivation Step 3: Substitution The proposed Cipher Lets take for example the following statement to illustrate our Techniques algorithm: “ ATTACK AT DAWN ” Encryption Decryption Results Conclusions 11 / 24 Encryption Project Step 1 Omar Hesham Ahmed Ali Each character is multiplied by a secret key depending to its position in Omar Nabil Youssef essam the text Karim Ahmed Motivation The proposed Cipher Techniques So now we will choose 5 and 11 as our keys Encryption Now each character is multiplied by either 5 or 11 depending on whether the position is even and odd respectively Decryption If position of character is even: Intermediate C.T. = [[character integral Results value*5] +1] mod (26) Conclusions If position of character is odd: Intermediate C.T. = [[character integral value*11] +1] mod (26) 12 / 24 Encryption Project Omar Hesham Applying all of this calculations on the following plain text: “ ATTACK Ahmed Ali Omar Nabil AT DAWN ” Youssef essam Karim Ahmed Motivation The proposed Cipher Techniques Encryption Decryption Results Conclusions 13 / 24 Encryption Project Step 2 Omar Hesham Ahmed Ali Here each character is written diagonally till 3 steps (rows) and then Omar Nabil Youssef essam read it in sequence of rows Karim Ahmed intermediate encrypted text (step one output): “BCSBLHBCQBHO” Motivation The proposed Cipher Techniques Encryption Decryption Now we will read it row wise so the output is: “BBBBCLCHSHQO ” Results Conclusions 14 / 24 Encryption Project Step 3 Omar Hesham Ahmed Ali each character is substituted with special symbols which provide it Omar Nabil Youssef essam double coat of substitution and hence make it more secure and Karim Ahmed encrypted Motivation The proposed Cipher Techniques Encryption Decryption Results Hence the text ”BBBBCLCHSHQO” is finally encrypted into “”””,(=(;/ Conclusions 15 / 24 Decryption Project Omar Hesham The decryption process is very similar to the encryption process Ahmed Ali Omar Nabil The difference is that all the steps is performed in reverse order Youssef essam Karim Ahmed Step 1 Motivation In this step, the encrypted text will be converted to the corresponding The proposed Cipher character value with the help of this table Techniques Encryption Decryption Results Conclusions Hence the corresponding intermediate decrypted text of the following encrypted text “”””,(=(;/ is ”BBBBCLCHSHQO” 16 / 24 Decryption Project Step 2 Omar Hesham Ahmed Ali In this step, the intermediate decrypted text obtained from step1 is Omar Nabil Youssef essam permuted in order to obtain the original position of the characters in the Karim Ahmed plain text Motivation Here, the text ”BBBBCLCHSHQO” is written in the sequence of rows The proposed Cipher and read in the sequence of diagonals Techniques Encryption Decryption Results Hence the corresponding intermediate decrypted text of the following Conclusions encrypted text ”BBBBCLCHSHQO” is ”BCSBLHBCQBHO” 17 / 24 Decryption Project Step 3 Omar Hesham Ahmed Ali It is the final step in decryption. Omar Nabil Youssef essam Here the intermediate text is decrypted into original Plain Text (P.T.) Karim Ahmed with the help of following formula: Motivation If position is even: P.T. = [[character integral value-1]*21] mod 26 The proposed Cipher Techniques If position is odd: P.T. = [[character integral value-1]*19] mod 26 Encryption Here, 21 and 19 are inverse of 5 and 11 respectively Decryption Results Conclusions 18 / 24 Decryption Project Step 3 Omar Hesham Ahmed Ali Applying this formula in the intermediate decrypted text Omar Nabil Youssef essam Karim Ahmed Motivation The proposed Cipher Techniques Encryption Decryption Results Conclusions Therefore, the original