1. CRYPTOGRAPHY – DES EMMANUEL M. BIBANGAMBA

2. TABLE OF CONTENTS Cryptography defined Definitions used Brief history of Cryptography DES & it’s history Technical details of DES Flow Chart on DES encryption An example on DES encryption (bits) Future of DES References Questions

3. CRYPTOGRAPHY DEFINED What is Cryptography? A process associated with scrambling plain text into cipher text, then back again. Cryptography’s four objectives: 1) Confidentiality 2) Integrity 3) Non-repudiation 4) Authentication

4. DEFINITIONS NSA – National Security Agency. NBS – National Bureau of Standards. NIST– National Institute of Standards and Technology Cipher - A design combining or interweaving letters or initials. FIPS- Federal Information Processing Standard

5. BRIEF HISTORY Cryptography began almost as early as when mankind started communicating in writing. Much of modern fame was gained during World War II with the cracking of the German Enigma code and the Japanese military cipher. The landmark discovery of cryptography’s intimate connection to mathematics.

6. DES AND IT’S HISTORY DES, an acronym for the Data Encryption Standard. The DEA is also defined in the ANSI standard X3.92. DES is an improvement of algorithm Lucifer, and it was assigned to IBM, Feistel’s employer

7. TECHNICAL DETAILS OF DES DES encryption takes as an input 64-bit block of plain text along with a 56-bit key. The encryption process takes place in 16 rounds in which a round function defined in terms of the S-boxes, is applied over and over with various sub keys of the 56-bit input key, which are generated according to a well defined scheme.

8. Flowchart for DES encryption Plain Text T LR F + L ◄ R R◄ L ØF(K,R) K1K1 L◄ R ØF(K,R)R T -1 CIPHER TEXT K 2 - K 16

9. FLOW CHART (Continued) In order to decrypt, the subkeys are used in reverse First let L(x) denotes the left half of a bit string x (assuming x has an even number of bits ) Let R (x) denote the right half, and C (x) be given by C(x) = R(x) || L(x)

10. FLOW CHART (Continued) For a 48-bit string k and a 64-bit plain text, Let f k (x) be given by f k (x) = (L(x) F(k, R(x)))||R(x). Then f k1 (x), f k2 (x),…,f k16 (x) are represented by the encircled plus sign, letter “F” and black dot +

11. DES EXAMPLE For example: DES is presented with plain texts X 1 = 00000000 00000000 0000000 0000000 00000000 00000000 00000000 00000000 and X 2 = 10000000 00000000 0000000 0000000 00000000 00000000 00000000 00000000 and the key K = 00000001 1001011 0100100 1100010 0011100 0011000 0011100 0110010 Then DES produces cipher texts that differ from one another in 34 positions.

12. FUTURE OF CRYPTOGRAPHY From e-mail to cellular communications, cryptography is an essential part of today's information systems. Cryptography helps provide accountability, fairness, accuracy, and confidentiality. But the cryptography now on the market doesn't provide the level of security it advertises. People who break cryptographic systems don't follow rules; they cheat.

13. REFERENCES www.stallion.com/html/support/glossary.htm Invitation to Cryptology.Thomas H. Barr Rhodes College. ISBN: 0-13-088976-8 http://www.rsasecurity.com/rsalabs/node.asp?id=2 226http://www.rsasecurity.com/rsalabs/node.asp?id=2 226 http://msdn.microsoft.com/library/default.asp?url= /library/e n- us/cpref/html/frlrfsystemsecuritycryptographydes classtopic.asphttp://msdn.microsoft.com/library/default.asp?url= /library/e n- us/cpref/html/frlrfsystemsecuritycryptographydes classtopic.asp http://www.schneier.com/essay-005.html

14. QUESTIONS ???????