DES

• This is more of a case study.
• But everyone should understand what is going on here.
• DES : Data Encryption Standard
  • Developed under the guidance of the US Government.
  • Data is encrypted with a 56 bit key
  • Data is processed in 64 bit blocks
    • Using only bitwise and basic arithmetic operations.
  • Substitution and Transportation
    • Substitution: The character's value is changed while the position remains the same.
    • Transportation: The character's position is changed, while the value remains the same.
  • Each of these is performed over and over again
    • In DES 16 cycles.
    • 
  • It takes turns mixing the bits and changing the bits with a given key.
  • It is reversible.
• A Brief Timeline
  • 1973 Development begins
  • 1977 Standard published.
  • 1998+ Brute force custom machines break code in days.
  • 2004 DES withdrawn as a standard.
  • 2016 - Brute force system with GPU hardware in 2 days
• The algorithm is fixed at a 56-bit key
  • So extending the key changes the algorithm.
  • Therefore people looked at other ways to enhance the algorithm.
• Double DES
  • Use two 56-bit keys and encrypt twice.
  • E($K_2$, E($E_1$,P))
  • This turns out to only be slightly better than the basic.
  • IE The key becomes a 57 bit key.
• Triple DES
  • E($K_1$, D($K_2$, E($K_1$,P))) is equivalent to a 80 bit key.
  • E($K_3$,E($K_2$, E($E_1$,P))) is equivalent to a 112 bit key
  • These are more secure.
• There have been problems with DES all along.
  • The Government sponsored the development.
  • The NSA stepped in and changed the proposed standard
    • There is a general belief that they weekend it to make it easier to crack.
    • Moore's law has degraded it over time.
    • Custom hardware has weekend it.