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Cryptographic Algorithms

Cryptographic Algorithms. By: Kirti Chawla. 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. Prologue. Introduction Classification

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Cryptographic Algorithms

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

  4. Algorithms Genealogy • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back Algorithms Ciphers Authenticators Symmetric Asymmetric DES\3DES AES IDEA RC6 BlowFish … … … RSA ELGAMAL … SHA MD5 …

  5. Algorithmic Parlance • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back Strong Open Key-oriented

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

  7. Deciding Operations Simple XOR • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back This is secret message This is key Axaw sa dawawt sazawcsr Modular arithmetic with polynomials This is secret message X7 + x5 + x2 + 1 This is key Axaw sa dawawt sazawcsr Relative prime factors This is secret message Factorized key1 Axaw sa dawawt sazawcsr Factorized key2

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

  9. Key Management Self-generation Ask from user • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back 1010 (data) 1010 XOR 11 = 1001 0101 (data) 0101 XOR 11 = 0110 Key organization Key protection 1010 0000 1010 1111 0000 1011 (key) 1010 0000 1010 (key) 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 management Padding • 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 … ! Boundary cases State management 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 • 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. Bi-directionality • 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. Symmetric Ciphers • 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. • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back

  13. Asymmetric Ciphers • 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. • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back

  14. Authenticators • 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. • Introduction • Classification • Algorithms • Vis-à-Vis • Looking back

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

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