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A Universal Encryption Standard

A Universal Encryption Standard. By Helena Handschuh Serge Vaudenay Presented by Amith Kumar Goel 2005H103023. Content. Introduction. Basic Notation and Building Blocks. UES – Algorithm. Key Schedule. Properties which makes it universal.

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A Universal Encryption Standard

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  1. A Universal Encryption Standard By Helena Handschuh Serge Vaudenay Presented by Amith Kumar Goel 2005H103023

  2. Content • Introduction. • Basic Notation and Building Blocks. • UES – Algorithm. • Key Schedule. • Properties which makes it universal. • Collision Attacks on Parallel DES(UES*) • Pre- and Post- operations. • Conclusion. A Universal Encryption Standard

  3. Introduction • Worldwide encryption standard is DES. • Key size became too short. • DES and 2-key triple DES have drawback of 64-bits block size. • Need for AES. • UES takes AES specification as requirement. • UES can also be use in place of DES and 2-key triple DES. A Universal Encryption Standard

  4. AES Specification • Should support block size of 128 bits. • The Key size should take possible values of 128,192,256 bits. • At least as secure and fast as triple DES. A Universal Encryption Standard

  5. Basic Notation • A|B : concatenation of A and B. • AB : bitwise “exclusive or” of A and B. • A^B : bitwise “and” of A and B. • DESk(x): DES encrypting block x using key k. • 3DESk1,k2(x) = DESk1 (DES-1k2 (DESk1(x))) (EDE mode) A Universal Encryption Standard

  6. Basic Building Blocks A 128-bits string x is spitted as xhand xl.. A Universal Encryption Standard

  7. UES Algorithm • It runs two triple DES encryption in parallel and exchange some bits in-between the encryption. • Let k’ = k1|k2|k3|k4 and m’ = m1|m2|m3|m4. be 256 bit extended key derived from k (256 bit) by key schedule. A Universal Encryption Standard

  8. The Key-Schedule • The user key for 128,192 or 256 bits is divided into s sub-keys of 64 bits block for s=2,3,4 respectively. • Here R0,R1…..R7 are 8 different key derived from 256 bits users key A Universal Encryption Standard

  9. The Key-Schedule (cont..) • Here E is the DES encryption in CBC mode with the fixed key k = 0123456789abcdefx and with the initial value set to zero. • Now from this 8 key derived first derive m1 and m2 than four key forming k’ and finally m3 and m4. A Universal Encryption Standard

  10. Algorithm (cont..)Let m = 00000000FFFFFFFFX A Universal Encryption Standard

  11. Algorithm (cont..) A Universal Encryption Standard

  12. PropertiesIf m’ = 0 , m = 0 and k’ = k. A Universal Encryption Standard

  13. Properties (cont..) • It operates on 128-bits block messages, and because of key schedule 128,192 and 256 bits key can be used. • This make algorithm compatible with AES. • It can also be use in DES or triple-DES mode. • After setting m=0,we can even run two full DES or 3DES encryption in parallel, which doubles the encryption speed (UES* only). A Universal Encryption Standard

  14. Collision Attacks • This straightforward way of doubling the block size is not secure. • The construction is not a multi permutation, In other words, It may happen that if half of the i/p bits have fixed value, half of the o/p bits will also be. • If the i/p and o/p bits of UES* is unknown than the collision attack is not possible. • Needs for additional layers in UES. A Universal Encryption Standard

  15. How to break UES* • Fix xh = a (constant) and try many xl = ui request yi|zi = UES*(a|ui). and it require 233 different key combination of k3. • Perform similar attack on k1. • Recover k2 and k4 by exhaustive search. A Universal Encryption Standard

  16. Pre- and Post- Operation The total complexity now is 278. A Universal Encryption Standard

  17. Conclusion • Thus we can use Universal Encryption Standard as the DES or triple DES as per today's standard. • We also saw that we can double the speed of UES when used in DES or 3DES mode. • It can also be plugged as AES as it full-fill AES requirement. • Practically impossible to recover key. A Universal Encryption Standard

  18. References • H.Handschuh, S.Vaudenay, “A Universal Encryption Standard.” • J.Kelsey, B.Schneier, “Key-Schedule Cryptanalysis of DEAL.” • L. Knudsen, “On Expanding the Block Length of DES.” • www.cryptography.com/cnews/hash.html A Universal Encryption Standard

  19. Thank You Queries ? A Universal Encryption Standard

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