Tutorial B5-2 Breaking DES (Straightforward)

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Follow the same procedure as in : Tutorial B5 Breaking AES (Straightforward), but:

  • Flashing the DES firmware to the target device (e.g. chipwhisperer/hardware/victims/firmware/simpleserial-des/simpleserial-des-xmega.hex), instead;

and:

  • Setting an appropriate 'Total Samples' (e.g. 3500) and 'Offset' (e.g. 15500) in the Scope Settings;
  • Setting the 'Key Length (Bytes)', 'Input Length (Bytes)' and 'Output Length (Bytes)' to 8 bytes in the Target Settings;
  • Setting an appropriate 8 bytes Key in the Generic Settings (e.g. 2B 7E 15 16 28 AE D2 A6).
  • Or, alternatively, execute the script "ChipWhisperer-Lite: DES SimpleSerial on XMEGA" to do the above steps automatically in this platform.

In the Analyzer, the only difference is to set the 'Crypto Algorithm' to DES in the Attack Settings.

Breaking des.png

Note that the attack attemps to recover the first round key, which only has 48bits (8 s-boxes x 6 bits each), while the original key has 56 significative bits (64 if we count the parity bits that are irrelevant). So, if we map the first round key, obtained after the attack, to the original key (you can use the provided DES Key Schedule Tool to do it), there will still be 8 bits missing (256 combinations).

Deskeyschedulecalc.png

In this example, it matches the original key that was:

Key des.png