They found the exact same backdoor key present on old NXP and Infineon cards produced as early as 1996. See p.11:
> But, quite surprisingly, some other cards, aside from the Fudan ones, accept the same backdoor authentication commands using the same key as for the FM11RF08!
> ...
> - Infineon SLE66R35 possibly produced at least during a period 1996-20136 ;
> - NXP MF1ICS5003 produced at least between 1998 and 2000 ;
> - NXP MF1ICS5004 produced at least in 2001.
> ...
> Additionally, what are we to make of the fact that old NXP and Infineon cards share the very same backdoor key?
> But, quite surprisingly, some other cards, aside from the Fudan ones, accept the same backdoor authentication commands using the same key as for the FM11RF08!
> ...
> - Infineon SLE66R35 possibly produced at least during a period 1996-20136 ;
> - NXP MF1ICS5003 produced at least between 1998 and 2000 ;
> - NXP MF1ICS5004 produced at least in 2001.
> ...
> Additionally, what are we to make of the fact that old NXP and Infineon cards share the very same backdoor key?