AES Advanced Encryption Standard

• A replacement for DES
  • Fixed blocksize of 128
  • Key sizes of 128, 192, 256 bits
  • Different number of rounds for different key sizes.
• Algorithm:
  • Round 1 Substitute
  • Round 2 Shift
  • Round 3 Mix
  • Round 4 Add a Key
  • 
• It can still be implemented on basic hardware.
• It is estimated that 128 bit key would take billions of years with current and forseeable hardware.
  • There have been some minor improvements in brute force.
  • The best I can find is to cut the time by 1/4
  • But this is still in the billions of years.
• Improvement over DES
  • Both the keysize and rounds in DES are fixed.
  • AES can be extended by changing either of these.
• I found it amusing that they warn about bad coding practices
  • P 99: "Remember, of course, that these strength figures apply on if the implementation and use are robust; a strong algorithm loses strength if used with a weakness that lets outsiders determine key properties of the encrypted data."
• They state that DES and AES are up to 10,000 times faster than RSA
  • Use RSA to exchange DES/AES keys
  • Use DES/AES to exchange message.