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Uploaded byAhmed Mohamed Mahmoud
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Trible data encryption standard (3DES)

This document provides an overview of the Triple Data Encryption Standard (3DES). It first briefly describes the original Data Encryption Standard (DES) and its key components including the initial and final permutations, substitution boxes, and key schedule. It then explains that 3DES applies DES three times with three different keys to strengthen security by effectively doubling the key size to 112 bits. Simulations are included showing encryption and decryption using 3DES with equal and different keys.

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Trible Data Encryption Standard (3DES) Prepared by: Ahmed Mohamed Ahmedmohamed.eece@gmail.com
Contents: Introduction: a short history of DES  Basic Terminology  DES  3DES  Simulations
Introduction: • The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST). • DES was developed as a standard for communications and data protection by an IBM research team, in response to a public request for proposals by the NBS - the National Bureau of Standards (which is now known as NIST).
Basic Terminology • plaintext - the original message • ciphertext - the coded message • cipher - algorithm for transforming plaintext to ciphertext • key - info used in cipher known only to sender/receiver • encipher (encrypt) - converting plaintext to ciphertext • decipher (decrypt) - recovering ciphertext from plaintext • Permutation !
Permutation: ……. …….. 1 2 3 4 32 22 6 13 32 3 Input: Output 0 0 1 0 1 1 0 1 1 1 1 bit
DES Key: 64 bit quantity=8-bit parity+56-bit key Every 8th bit is a parity bit. 64 bit input, 64 bit output.
DES STRUCTURE
Initial and Final Permutations
Continue
Example: • Find the output of the initial permutation box when the input is given in hexadecimal as: • Solution: Only bit 25 and bit 63 are 1s; the other bits are 0s. In the final permutation, bit 25 becomes bit 64 and bit 63 becomes bit 15. The result is
Initial Permutations VHDL Code
Note
DES top view Permutation Permutation Swap Round 1 Round 2 Round 16 Generate keys Initial Permutation 48-bit K1 48-bit K2 48-bit K16 Swap 32-bit halves Final Permutation 64-bit Output 48-bit K164-bit Input 56-bit Key …...
DES 64 bit plaintext block IP L0 R0 L1=R0 R1=L0 f(R0,K1) f K1 (derived from 56 bit key)=48 bit L16=R15 f K16 (derived from 56 bit key)= 48 bit IP-1 repeat 16 times… 64 bit ciphertext block R16=L15 f(R15,K16) 32 32  
Per-Round Key Generation 28 bits 28 bits 48 bits Ki One round Circular Left Shift Circular Left Shift 28 bits 28 bits Permutation with Compression, PC-2 Initial Permutation of DES key ,PC-1 C i-1 D i-1 C i D i
Key generation:
• Parity-bit drop table: Key-compression table:
Rounds 𝐿 𝑛 = 𝑅 𝑛−1
L0 R0 L1 R1 48 bit subkey Generator K48 = g(i,K56) (The key for each round is deterministically found from the input 56 bit key). Expansion Permutation S-Box Substitution P-Box Permutation 32 48 48 48 32 32 3232 32
Expansion P-box • Since RI−1 is a 32-bit input and KI is a 48-bit key, we first need to expand RI−1 to 48 bits.
Continue • Although the relationship between the input and output can be defined mathematically, DES uses Table to define this P-box.
Expansion P-box VHDL Code
S-Boxes • The S-boxes do the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output.
S-box rule S-box 1 14 4 13 1 2 15 11 8 3 10 6 12 5 9 0 7 0 15 7 4 14 2 13 1 10 6 12 11 9 5 3 8 4 1 14 8 13 6 2 11 15 12 9 7 3 10 5 0 15 12 8 2 4 9 1 7 5 11 3 14 10 0 6 13 Pageselect
Example: • The input to S-box 1 is 100011. What is the output? • Answer: • If we write the first and the sixth bits together, we get 11 in binary, which is 3 in decimal. The remaining bits are 0001 in binary, which is 1 in decimal. We look for the value in row 3, column 1, in Table (S-box 1). • The result is 12 in decimal, which in binary is 1100. So the input 100011 yields the output 1100.
S-Box1 VHDL Code And So on ..
Straight Permutation
Straight Permutation VHDL Code
Decryption • The same algorithm as encryption. • Reversed the order of key (Key16, Key15, … Key1). • For example: IP undoes IP-1 step of encryption. 1st round with SK16 undoes 16th encrypt round.
DES Security: • Not too good: • Trying all 256 possible keys is not that hard these days. • If you spend ~$25k you can build a DES password cracker that can will succeed in a few hours. • The major criticism of DES regards its key length. Fortunately DES is not a group. This means that we can use double or triple DES to increase the key size.
Triple DES - More Secure True cryptographic strength of 3DES key is 2x56 bits = 112 bits Ci  EK3 DK2 EK1 Pi   
Triple DES - More Secure Triple DES with two keys • Run DES three times Why Encrypt then Decrypt then Encrypt with 2 keys?! • Backwards compatibility • If K2 = K3, this is DES E(D(E(P,K),K),K)= E(P,K) C=E(D(E(P,K1),K2),K1) P=D(E(D(C,K1),K2),K1)
Comparison
Simulation:K1=K2=K3: Encryption
Simulation:K1=K2=K3: Decryption
Simulation:K1=K3: Encryption
Simulation:K1=K3: Decryption
Simulation:K1≠K2≠K3: Encryption
Simulation:K1≠K2≠K3: Decryption
Any Questions ? Thank You