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    Simplified DES 1: 2.1 Key Generation

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    Rimbun Ferianto Sr
    1) This document describes a simplified version of the Data Encryption Standard (DES) algorithm to demonstrate how it works. 2) It walks through a full example of encrypting the plaintext "0010 1000" using the 10-bit key "1100011110" with the simplified DES. 3) The encryption results in the ciphertext "1000 1010" after applying the initial and final permutations, two encryption rounds using the derived subkeys, and substitution and permutation functions.

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    Simplified DES 1: 2.1 Key Generation

    Uploaded by

    Rimbun Ferianto Sr
    162 views3 pages
    1) This document describes a simplified version of the Data Encryption Standard (DES) algorithm to demonstrate how it works. 2) It walks through a full example of encrypting the plaintext "0010 1000" using the 10-bit key "1100011110" with the simplified DES. 3) The encryption results in the ciphertext "1000 1010" after applying the initial and final permutations, two encryption rounds using the derived subkeys, and substitution and permutation functions.

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    Algoritma DES

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    1) This document describes a simplified version of the Data Encryption Standard (DES) algorithm to demonstrate how it works. 2) It walks through a full example of encrypting the plaintext "0010 1000" using the 10-bit key "1100011110" with the simplified DES. 3) The encryption results in the ciphertext "1000 1010" after applying the initial and final permutations, two encryption rounds using the derived subkeys, and substitution and permutation functions.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    162 views3 pages

    Simplified DES 1: 2.1 Key Generation

    Uploaded by

    Rimbun Ferianto Sr
    1) This document describes a simplified version of the Data Encryption Standard (DES) algorithm to demonstrate how it works. 2) It walks through a full example of encrypting the plaintext "0010 1000" using the 10-bit key "1100011110" with the simplified DES. 3) The encryption results in the ciphertext "1000 1010" after applying the initial and final permutations, two encryption rounds using the derived subkeys, and substitution and permutation functions.

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    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
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    ISE334: Com.

    and E-Commerce Security Semester 2 5773

    Recitation 3 4 April 2013

    Simplied DES 1 Introduction

    In this lab we will work through a simplied version of the DES algorithm. The algorithm is not cryptographically secure, but its operations are similar enough to the DES operation to give a better feeling for how it works. We will proceed by reading the Simplied DES algorithm description in the Stallings section. We will then work through a full example in class.

    Full Example

    Let the plaintext be the string 0010 1000. Let the 10 bit key be 1100011110.

    2.1

    Key Generation

    The keys k1 and k2 are derived using the functions P 10, Shift, and P 8. P 10 is dened as follows: 3 P 8 is dened to be as follows: 6 The rst key k1 is therefore equal to: Bit # 1 2 3 4 K 1 1 0 0 P 10(K ) 0 0 1 1 Shif t(P 10(K )) 0 1 1 0 P 8(Shif t(P 10(K ))) 1 1 1 0 The second key k2 is derived in Bit # 1 2 K 1 1 P 10(K ) 0 0 Shif t3 (P 10(K ))) 1 0 P 8(Shif t2 (P 10(K ))) 1 0 3 5 0 0 0 1 7 6 1 0 1 0 4 7 1 1 1 0 P8 8 8 1 1 1 1 8 1 1 0 1 5 9 1 1 1 10 10 0 1 0 9 5 2 7 4 P10 10 1 9 8 6

    a similar manner: 3 4 5 6 7 0 0 0 1 1 1 1 0 0 1 0 0 1 1 1 1 0 0 1 1

    9 1 1 1

    10 0 1 1

    So we have the two keys k1 = {1110 1001} and k2 = {1010 0111}

    2.2

    Initial and Final Permutation

    The plaintext undergoes an initial permutation when it enters the encryption function, IP . It undergoes a reverse nal permutation at the end IP 1 . The function IP is dened as follows:

    IP 2 6 3 1 4 8 5 7 The function IP 1 is dened as follows: 4 1 3 IP 1 5 7 2 we 4 0 0 8 6

    Applied to the input, Bit # 1 2 3 P 0 0 1 IP (P ) 0 0 1

    have the following after the initial permutation: 5 6 7 8 1 0 0 0 0 0 1 0

    2.3

    Functions fK , SW , K

    The function fk is dened as follows. Let P = (L, R), then fK (L, R) = (L F (R, SK ), R). The function SW just switches the two halves of the plaintext, so SW (L, R) (R, L) The function F (p, k ) takes a four bit string p and eight bit key k and produces a four bit output. It performs the following steps. 1. First it runs an expansion permutation E/P : E/P 4 1 2 3 2 3 4 1 2. Then it XORs the key with the result of the E/P function 3. Then it substitutes the two halves based on the S-Boxes. 4. Finally, the output from the S-Boxes undergoes the P 4 permutation: P4 2 4 3 1

    Applying the functions, we must perform the following steps: IP 1 fK2 SW fK1 IP 1. We have already calculated IP (P ) = {0010 0010}. Applying the next functions: 2. fK1 (L, R) = f{1110
    1001} (0010

    0010) = (0010 F (0010, {1110 1001}), 0010)

    3. F (0010, {1110 1001}) = P 4 SBoxes {1110 1001} (E/P (0010)) 4. The steps are: Bit # R E/P(R) k1 E/P(R)k1 SBoxes(E/P(R)k1 ) P4(Sboxes(E/P(R)k1 )) 1 0 0 1 1 1 0 2 0 0 1 1 0 0 3 1 0 1 1 0 0 4 0 1 0 1 0 1 5 0 1 1 6 1 0 1 7 0 0 0 8 0 1 1

    5. The result from F is therefore 0001 6. Calculating we then have fk1 (L, R) = (0010 0001, 0010) = (0011, 0010) 7. So far, then L = 0011 and R = 0010. SW just swaps them so R = 0011 and L = 0010. 8. We now do the calculation of fk2 (L, R) = f{1010
    0111} (0010

    0011) = (0010 F (0011, {1010 0111}, 0011))

    9. The steps for F are as above: Bit # R E/P(R) k2 E/P(R)k2 SBoxes(E/P(R)k2 ) P4(Sboxes(E/P(R)k2 )) 1 0 1 1 0 1 0 2 0 0 0 0 0 0 3 1 0 1 1 1 1 4 1 1 0 1 0 1 5 0 0 0 6 1 1 0 7 1 1 0 8 0 1 1

    10. So now we have the outcome of F as 0011 11. Calculating we then have fk2 (L, R) = (0010 0011, 0011) = (0001, 0011) 12. Last, we perform the IP 1 permutation: Bit # R,L IP 1 (R,L) 1 0 1 2 0 0 3 0 0 4 1 0 5 0 1 6 0 0 7 1 1 8 1 0

    13. So the nal result of the encryption is 1000 1010.

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