Wednesday, July 2, 2014

CCID descriptor statistics: dwMaximumClock

Article from the serie "CCID descriptor statistics"

The dwMaximumClock field is a number value from the USB CCID descriptor:
Maximum supported ICC clock frequency in KHz. This is an integer value.
Example: 14.32 MHz is encoded as the integer value 14320. (000037F0h)

dwMaximumClock#%
4.000 MHz9437.01 %
8.000 MHz4316.93 %
3.580 MHz3312.99 %
12.000 MHz176.69 %
3.700 MHz103.94 %
4.800 MHz103.94 %
13.560 MHz83.15 %
7.500 MHz62.36 %
4.615 MHz51.97 %
1.500 MHz41.57 %
20.000 MHz31.18 %
3.570 MHz31.18 %
3.600 MHz31.18 %
1.000 MHz20.79 %
3.571 MHz20.79 %
3.692 MHz20.79 %
1024.000 MHz10.39 %
16.000 MHz10.39 %
2.000 MHz10.39 %
3.000 MHz10.39 %
3.685 MHz10.39 %
3.686 MHz10.39 %
3.850 MHz10.39 %
4.714 MHz10.39 %
5.000 MHz10.39 %

We find nearly the same values as for dwDefaultClock (See CCID descriptor statistics: dwDefaultClock):
  • 4.0 Mhz: (37% of readers), 48% of readers have a default clock of 4.0 Mhz
  • 8.0 Mhz: (17%) this is just the double of a default clock of 4.0 Mhz
  • 3.58 Mhz: (13%) same as default clock for 34 readers
  • 12 Mhz: (7%) 3 times the default clock of 4.0 Mhz

The maximum clock speeds are more diverse than the default clock speeds.

If we draw the number of reader per clock frequency we have:

The value 1024 Mhz (1.024 GHz) is, here again, clearly from a bogus reader.