Data Encryption Standard Simplified-DES Details of DES DES in - - PowerPoint PPT Presentation

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Data Encryption Standard Simplified-DES Details of DES DES in - - PowerPoint PPT Presentation

Oct 06, 2022 276 likes •602 views

Cryptography Data Encryption Standard Overview of the Data Encryption Standard (DES) Data Encryption Standard Simplified-DES Details of DES DES in OpenSSL Cryptography DES in Python School of Engineering and Technology CQUniversity

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Data Encryption Standard

Cryptography

School of Engineering and Technology CQUniversity Australia

Prepared by Steven Gordon on 19 Feb 2020, des.tex, r1788

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Cryptography Data Encryption Standard Overview of the Data Encryption Standard (DES) Simplified-DES Details of DES DES in OpenSSL DES in Python

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Contents

Overview of the Data Encryption Standard (DES) Simplified-DES Details of DES DES in OpenSSL DES in Python

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Data Encryption Standard

◮ Symmetric block cipher ◮ 56-bit key, 64-bit input block, 64-bit output block ◮ Developed in 1977 by NIST; designed by IBM (Lucifer) with input from NSA ◮ Principles used in other ciphers, e.g. 3DES, IDEA

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Contents

Overview of the Data Encryption Standard (DES) Simplified-DES Details of DES DES in OpenSSL DES in Python

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Simplified DES

◮ Input (plaintext) block: 8-bits ◮ Output (ciphertext) block: 8-bits ◮ Key: 10-bits ◮ Rounds: 2 ◮ Round keys generated using permutations and left shifts ◮ Encryption: initial permutation, round function, switch halves ◮ Decryption: Same as encryption, except round keys used in opposite order

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S-DES Algorithm

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S-DES Permutations (definition)

Permutations used in S-DES: P10 (permutate) Input : 1 2 3 4 5 6 7 8 9 10 Output: 3 5 2 7 4 10 1 9 8 6 P8 (select and permutate) Input : 1 2 3 4 5 6 7 8 9 10 Output: 6 3 7 4 8 5 10 9 P4 (permutate) Input : 1 2 3 4 Output: 2 4 3 1 EP (expand and permutate) Input : 1 2 3 4 Output: 4 1 2 3 2 3 4 1 IP (initial permutation) Input : 1 2 3 4 5 6 7 8 Output: 2 6 3 1 4 8 5 7

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Other Operations in S-DES

◮ LS-1: left shift by 1 position ◮ LS-2: left shift by 2 positions ◮ IP−1: inverse of IP, such that X = IP−1(IP(X)) ◮ SW: swap the halves ◮ fK: a round function using round key K ◮ F: internal function in each round ◮ Angled lines through arrows with a number next to them indicate the number of bits passing between the blocks

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S-DES Key Generation

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S-DES Encryption

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S-DES S-Boxes (definition)

S-Box considered as a matrix: input used to select row/column; selected element is output 4-bit input: bit1, bit2, bit3, bit4 bit1bit4 specifies row (0, 1, 2 or 3 in decimal) bit2bit3 specifies column S0 =     01 00 11 10 11 10 01 00 00 10 01 11 11 01 11 10     S1 =     00 01 10 11 10 00 01 11 11 00 01 00 10 01 00 11    

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Encrypt with S-DES (exercise)

Show that when the plaintext 01110010 is encrypted using S-DES with key 1010000010 that the ciphertext obtained is 01110111.

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S-DES Summary

◮ Educational encryption algorithm ◮ S-DES expressed as functions: ciphertext = IP−1 (fK2 (SW (fK1 (IP (plaintext))))) plaintext = IP−1 (fK1 (SW (fK2 (IP (ciphertext))))) ◮ Brute force attack on S-DES is easy since only 10-bit key ◮ If know plaintext and corresponding ciphertext, can we determine key? Very hard

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S-DES Compared to Real DES

◮ S-DES vs DES ◮ Block size: 8 bits vs 64 bits ◮ Rounds: 2 vs 16 ◮ IP: 8 bits vs 64 bits ◮ F: 4 bits vs 32 bits ◮ S-Boxes: 2 vs 8 ◮ Round key: 8 bits vs 48 bits

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Contents

Overview of the Data Encryption Standard (DES) Simplified-DES Details of DES DES in OpenSSL DES in Python

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General DES Encryption Algorithm

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Permutation Tables for DES

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Permutation Tables for DES

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Single Round of DES Algorithm

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Calculation of F(R,K)

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Definition of DES S-Boxes

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Definition of DES S-Boxes

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DES Key Schedule Calculation

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Contents

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DES Key Generation (exercise)

Generate a shared secret key to be used with DES and share it with another person.

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DES Encryption (exercise)

Create a message in a plain text file and after using DES, send the ciphertext to the person you shared the key with.

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DES Decryption (exercise)

Decrypt the ciphertext you received.

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Contents

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AES in Python Cryptography Library

◮ cryptography.io/en/latest/hazmat/primitives/symmetric- encryption/