Data Encryption   Standard
Introduction●   The Data Encryption Standard (DES) is a    symmetric-key block cipher published by the    National Institu...
OverviewDES is a block cipher, as shown in Figure 6.1.
Structure of DES
Initial and Final Permutation
Intial and final permutation tables
The initial and finalpermutations are straight P-boxes that are inversesof each other. They have nocryptography significan...
Feistel cipher
DES functionThe heart of DES is the DES function. The DESfunction applies a 48-bit key to the rightmost 32bits to produce ...
Expansion P-boxSince RI−1 is a 32-bit input and KI is a 48-bit key, wefirst need to expand RI−1 to 48 bits. Although the r...
(XOR)After the expansion permutation, DES uses theXOR operation on the expanded right section andthe round key. Note that ...
S-Boxes
S-Box Rule
S-Box 1
Straight Permutation Table
Algorithm for DESCipher(plain[64],keys[16,48],cipher[64]){permute(64,64,plain,inblock,IniPerTab)split(64,32,inblock,left,r...
mixer(left[32],right[32],keys[48]){    Copy(32,right,T1)    function(T1,keys,T2)    XOR(32,left,T2,T3)    Copy(32,T3,right...
function(input[32],key[48],output[32]){    Permute(32,48,input,T1,ExpansionPerTab)    XOR(48, T1, key, T2)    substitute(T...
Completeness Effect●   One bit of cipher text depends upon more    than one bit.●   And in DES the cipher text shows    co...
References●   Behrouz Forouzan analysis
Thank You●   Find the presentation on:-    www.slideshare.com/anshuljmi
Des
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Des

  1. 1. Data Encryption Standard
  2. 2. Introduction● The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).● In 1973, NIST published a request for proposals for a national symmetric-key cryptosystem. A proposal from IBM, a modification of a project called Lucifer, was accepted as DES. DES was published in the Federal Register in March 1975 as a draft of the Federal Information Processing Standard (FIPS).
  3. 3. OverviewDES is a block cipher, as shown in Figure 6.1.
  4. 4. Structure of DES
  5. 5. Initial and Final Permutation
  6. 6. Intial and final permutation tables
  7. 7. The initial and finalpermutations are straight P-boxes that are inversesof each other. They have nocryptography significance inDES.
  8. 8. Feistel cipher
  9. 9. DES functionThe heart of DES is the DES function. The DESfunction applies a 48-bit key to the rightmost 32bits to produce a 32-bit output.
  10. 10. Expansion P-boxSince RI−1 is a 32-bit input and KI is a 48-bit key, wefirst need to expand RI−1 to 48 bits. Although the relationship between the input and output can be defined mathematically, DES uses Table to define this P-box.
  11. 11. (XOR)After the expansion permutation, DES uses theXOR operation on the expanded right section andthe round key. Note that both the right section andthe key are 48-bits in length. Also note that theround key is used only in this operation.
  12. 12. S-Boxes
  13. 13. S-Box Rule
  14. 14. S-Box 1
  15. 15. Straight Permutation Table
  16. 16. Algorithm for DESCipher(plain[64],keys[16,48],cipher[64]){permute(64,64,plain,inblock,IniPerTab)split(64,32,inblock,left,right)for(round =1 to 16){ mixer(left,right,keys[i]) if(round!=16) swapper(left,right)}combine(32,64,left,right,outblock)permute(64,64,outblock,cipher,FinPerTab)}
  17. 17. mixer(left[32],right[32],keys[48]){ Copy(32,right,T1) function(T1,keys,T2) XOR(32,left,T2,T3) Copy(32,T3,right)}swapper(left[32],right[32]){ Copy(32,left,T) Copy(32,right,left) Copy(32,T,right)}
  18. 18. function(input[32],key[48],output[32]){ Permute(32,48,input,T1,ExpansionPerTab) XOR(48, T1, key, T2) substitute(T2,T3,SubstituteTab) Permute(32,32,T3,output,StraightPerTab)}
  19. 19. Completeness Effect● One bit of cipher text depends upon more than one bit.● And in DES the cipher text shows completeness effect.
  20. 20. References● Behrouz Forouzan analysis
  21. 21. Thank You● Find the presentation on:- www.slideshare.com/anshuljmi

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