ATR statistics: TD2 - Structural, encodes Y3 and T

Article from the series "ATR statistics"

TD2 - Structural, encodes Y3 and T

The ISO 7816-3 specification is not public. So I can't copy/paste part of the text. I will use Wikipedia instead.

Refer to TD1 - Structural, encodes Y2 and T since the definition of TD₂ is identical to TD₁.

TD2	#	%
	1123	54.20 %
0x31	393	18.97 %
0x01	250	12.07 %
0x1F	178	8.59 %
0x71	50	2.41 %
0xB1	48	2.32 %
0x91	10	0.48 %
0x21	6	0.29 %
0x3F	5	0.24 %
0xF1	5	0.24 %
0x10	2	0.10 %
0x11	2	0.10 %

TD₂ (as the other TD_i bytes) is structural and indicates:

• How to interpret the other ATR bytes
• What communication protocol the card wants to use

For 54% of the ATRs no TD₂ is present. So no other TA₃, TB₃, TC₃ or TD₃ is present and no new protocol is defined so the protocol defined by TD₁ (if any) will be used.

For 19% of the ATRs TD₂ = 0x31. The high nibble is 0011b so TA₃, TB₃ are present and T=1 protocol is defined. One such ATR is 3B 82 81 31 76 43 C0 02 C5.

For 12% of ATRs TD₂ = 0x01. The high nibble is 0000b so no other TA₃, TB₃, TC3 or TD₃ is present and T=1 protocol is defined. One such ATR is 3B 84 80 01 00 00 90 00 95.

0.10% of cards have TD₂ = 0x10 and so (re)define the use of T=0. In fact what is important here is the high nibble of TD₂ 0001b that defines that TA₃ is present. One such ATR is 3B DD 96 00 80 10 FE 80 31 80 63 01 FF C0 73 B3 21 1B 81 05.

I will not document all the other cases. I let this exercise to the reader.