On Mon, Oct 24, 2016 at 10:10:20PM +0200, Maxime Ripard wrote: > On Sat, Oct 22, 2016 at 03:53:28PM +0200, Corentin Labbe wrote: > > Since SID's content is constant over reboot, > > That's not true, at least not across all the Allwinner SoCs, and > especially not on the A10 and A20 that this driver supports. > On my cubieboard2 (A20) hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem 00000000 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000100 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| 00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000200 cubiedev ~ # reboot cubiedev ~ # hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem 00000000 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000100 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur| 00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000200 So clearly for me its constant. > > it must not be used as source of randomness. > > And I don't think that's true either. A constant entropy provider will > not add any entropy, but will not remove any, would it? I cced linux-crypto at the begining for confirmation on that. But the problem is increased as a part of the content is predicatable over same type of device (at least the thirst bytes and all the zeros). -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
