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Encryption for Mobile Computing

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This document explores a range of encryption algorithms pivotal to mobile computing, including DES, 3DES, RC5, RC6, and Twofish. It details the historical context, operational mechanisms, and strengths of each algorithm. DES, established in the 1970s, is contrasted with more modern options like RC5 and Twofish, which prioritize speed and flexibility. The report analyzes core operations like rotational shifts, XOR, and permutation, and discusses their impact on processing efficiency in mobile devices. Recommendations for optimizing encryption on current processors are also included.

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Encryption for Mobile Computing

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  1. Encryption for Mobile Computing By Erik Olson Woojin Yu

  2. Encryption Algorithms • DES and 3DES • RC5 • RC6 – AES Finalist • Twofish- AES Finalist

  3. DES and 3DES • DES - International Standard, 1970’s • 3DES – repeated encryption with DES • Extensive usage of permutation, table look-ups, and rotational shifts • 56 bit key – weak encryption

  4. RC5 • Fast block cipher • By Ron Rivest at RSA in 1994 • Based on integer addition, data dependent rotational shifts and XOR’s • Very simple, but powerful • Patented

  5. RC6 • Based on RC5 algorithm • One finalist for AES • 128 bit blocks for AES • Flexible

  6. Twofish • AES finalist • XOR’s, 32 bit and 4 bit rotational shifts, table lookups, and matrix operations • Scalable and parameterizable • Some operations can be done in parallel

  7. Processor in Our Survey • Motorola DragonBall EZ - 68K core - Primarily used in Palm Pilots - 16.58 Mhz - 2.7 MIPS rating

  8. Setup and Makekey • Shifts and Rotational Shifts • A=A>>8 • ROTL(x,n)= (x<<(n & 0x1f))|(x >> 0x20-(n&0x1f)) • Word Swapping • A->B, B->A • Extensive usage of loops • Array operations • S[I]=S[I-1]+4

  9. 3DES Setup

  10. RC5 Setup

  11. RC6 Setup

  12. Twofish Setup

  13. Core Operations • Rotational Shifts • ROTL(x,n)= (x<<(n & 0x1f))|(x >> 0x20-(n&0x1f)) • ROTR(x,n)= (x>>(n & 0x1f))|(x << 0x20-(n&0x1f)) • XOR • A=A^B

  14. Core Op Cont’d • Integer Operations • A=A+S[0] • Bit Permutation • A=01001110 SP={5,7,1,3,2,8,4,6} A=11001001 after permutation • Using Constants • P=0xb7e15163, • A=A^P

  15. 3DES Core

  16. RC5 Core

  17. RC6 Core

  18. Twofish Core

  19. Analysis & Improvement • Using Rotational Shift instruction • Implementing special shifting unit • LSR and LSL dominate the clock cycles • Minimize Move Instruction/Penalty

  20. Analysis Cont’d • Improvement using ROT instruction • 1.5 times speed up in encryption core • Improvement using fast rotation HW • 2 times speed up in encryption core

  21. Analysis Cont’d • 3DES Core • 6.1 Kbps • RC5 Core • 121 Kbps • Improved version : 272 Kbps • RC6 Core • 87 Kbps • Improved version : 187 Kbps • Twofish • 12.8 Kbps

  22. Conclusion • Dominance of shifts and rotational shifts in all encryption algorithms • Limited improvement provided by the specialized hardware • Importance of algorithm choice for optimal usage

  23. Future Recommendations • Analysis on Windows CE processors – Hitachi SH3 and StrongArm • Analysis involving more instruction parallelism • Analysis on configurable processors - Tensilica

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