1. By: Kirti Chawla

2. Introduction Classification Algorithms Vis-à-Vis Looking back What is a Cipher or Crypto-algorithm ? A method or system for transforming given information in order to conceal its meaning.

3. Introduction Classification Algorithms Vis-à-Vis Looking back Transposition ciphers Prologue Substitution ciphers Transposition Substitution Computers Can Only Execute Answers CCOEAoan xnmnlesp _ycwu__u et__tre_ _ess____ Computers Can Only Execute Answers Frpsxwhuv Fdq Rqob Hahfxwh Dqvzhuv

4. Introduction Classification Algorithms Vis-à-Vis Looking back Algorithms Genealogy Algorithms CiphersAuthenticators AsymmetricSymmetric DES\3DES AES IDEA RC6 BlowFish … RSA ELGAMAL … SHA MD5 …

5. Algorithmic Parlance Introduction Classification Algorithms Vis-à-Vis Looking back Strong OpenKey-oriented

6. At the heart of Algorithms Introduction Classification Algorithms Vis-à-Vis Looking back Methods to do Categories Directional Behavior Anomalous Behavior Handling Key Management Controlled Chaos Creation Deciding Operations 1.Simple XOR 2.Modular Arithmetic with Polynomials 3.Relative Prime Factors 1.S-boxes & P-boxes 2.Inversion 3.Data distribution/redundancy 1.Self generation or ask from user 2.Key organization 3.Key protection 1.Buffer management 2.Padding and boundary cases 3.State management 1.Hash or One time PADs 2.Bi-directionality

7. Deciding Operations Introduction Classification Algorithms Vis-à-Vis Looking back This is secret message This is key Axaw sa dawawt sazawcsr This is secret message X 7 + x 5 + x 2 + 1 This is key Axaw sa dawawt sazawcsr This is secret message Factorized key 1 Factorized key 2 Axaw sa dawawt sazawcsr Simple XOR Modular arithmetic with polynomials Relative prime factors

8. Controlled Chaos Creation Introduction Classification Algorithms Vis-à-Vis Looking back S-boxP-box InversionData distribution/redundancy 1010 (data) 001 1010 0101(data) 1010 001

9. Key Management Introduction Classification Algorithms Vis-à-Vis Looking back Self-generationAsk from user 1010 (data) 1010 XOR 11 = 1001 0101 (data) 0101 XOR 11 = 0110 Key organization 1010 0000 1010 1111 0000 1011 (key) 1010 0000 1010 (key) Key protection 1010 0000 1010 1111 0000 1011 (key) 1010 0000 1010 1111 0000 1010 1010

10. Anomalous Behavior Handling Introduction Classification Algorithms Vis-à-Vis Looking back Buffer managementPadding Boundary casesState management 1010 1000 0010 1100 [+] 1000 1001 = Overflow Capture of 1010 1000 0010 1100 as plain-text from buffer on which algorithm operate If the input data or key are not exactly fulfilling the algorithm requirements, lets say required input is of multiple of 2 and > 512 bit, but user does not provide … ! U/SIGN-INT * U/SIGN-INT > 65536/32768 If the algorithm works in various stages, each stage signifying a state and regurgitating partially (weak) cipher-text and hence making possible ‘interleaving’… !

11. Directional Behavior Introduction Classification Algorithms Vis-à-Vis Looking back Hash or one time PADs Bi-directionality Use one character once only for substitution. Destroy or delete encryption mechanism. Destroy or delete decryption mechanism. Hash differs from one time PADs in a way of producing output. Given the single algorithm, the enciphering and deciphering operations should be inverse of each other. Bi-directional nature of algorithm is there, because of need to get original data back.

12. A single key for enciphering and deciphering operations. More the number of bits of key, more secure your data. Algorithms are usually characterized as stream or block ciphers. Algorithmic proclivity to certain weak keys can create problem. Used generally for protecting data. Symmetric Ciphers Introduction Classification Algorithms Vis-à-Vis Looking back

13. One key for enciphering and another key for deciphering operation. More the distance between mutually prime nos. ( here they are key ), more secure your data. Used generally for protecting data as well for making sure its authentication. Asymmetric Ciphers Introduction Classification Algorithms Vis-à-Vis Looking back

14. Hash functions gives a fixed-length output for a arbitrary-length message. Strength of algorithm is measured by collision resistance. Uni-directionality is innate capability of authentication algorithms. Authentication is achieved by re-computing hash and compared with stored hash value. Authenticators Introduction Classification Algorithms Vis-à-Vis Looking back

15. Introduction Classification Algorithms Vis-à-Vis Looking back Egyptian pictorial substitution Caesar cipher Cipher cylinders Enigma DES/… algorithms