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pysim/pcsc: do not use getProtocol for protocol selection

The documentation of the getProtocol provided by pyscard says:

"Return bit mask for the protocol of connection, or None if no
protocol set. The return value is a bit mask of
CardConnection.T0_protocol, CardConnection.T1_protocol,
CardConnection.RAW_protocol, CardConnection.T15_protocol"

This suggests that the purpose of getProtocol is not to determine
which protocols are supported. Its purpose is to determine which
protocol is currently selected (either through auto selection or
through the explicit selection made by the API user). This means
we are using getProtocol wrong.

So far this was no problem, since the auto-selected protocol
should be a supported protocol anyway. However, the automatic
protocol selection may not always return a correct result (see
bug report from THD-siegfried [1]).

Let's not trust the automatic protocol selection. Instead let's
parse the ATR and make the decision based on the TD1/TD2 bytes).

[1] https://osmocom.org/issues/6952

Related: OS#6952
Change-Id: Ib119948aa68c430e42ac84daec8b9bd542db7963
---
M pySim/transport/pcsc.py
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/pySim/transport/pcsc.py b/pySim/transport/pcsc.py
index c92a3ba..21d3ce4 100644
--- a/pySim/transport/pcsc.py
+++ b/pySim/transport/pcsc.py
@@ -26,6 +26,7 @@
 from smartcard.Exceptions import NoCardException, CardRequestTimeoutException, CardConnectionException
 from smartcard.System import readers
 from smartcard.ExclusiveConnectCardConnection import ExclusiveConnectCardConnection
+from smartcard.ATR import ATR
 
 from osmocom.utils import h2i, i2h, Hexstr
 
@@ -84,18 +85,21 @@
             self.disconnect()
 
             # Make card connection and select a suitable communication protocol
+            # (Even though pyscard provides an automatic protocol selection, we will make an independent decision
+            #  based on the ATR. There are two reasons for that:
+            #  1) In case a card supports T=0 and T=1, we perfer to use T=0.
+            #  2) The automatic protocol selection may be unreliabe on some platforms
+            #     see also: https://osmocom.org/issues/6952)
             self._con.connect()
-            supported_protocols = self._con.getProtocol();
-            self.disconnect()
-            if (supported_protocols & CardConnection.T0_protocol):
-                protocol =  CardConnection.T0_protocol
+            atr = ATR(self._con.getATR())
+            if atr.isT0Supported():
+                self._con.setProtocol(CardConnection.T0_protocol)
                 self.set_tpdu_format(0)
-            elif (supported_protocols & CardConnection.T1_protocol):
-                protocol = CardConnection.T1_protocol
+            elif atr.isT1Supported():
+                self._con.setProtocol(CardConnection.T1_protocol)
                 self.set_tpdu_format(1)
             else:
                 raise ReaderError('Unsupported card protocol')
-            self._con.connect(protocol)
         except CardConnectionException as exc:
             raise ProtocolError() from exc
         except NoCardException as exc:

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