In the following you see a snippet of my Python program that I wrote to send APDU commands to smart cards. I used PySCard library in this program.
First Program :
for LOAD_KEY in validLoadCommands:
data,sw1,sw2 =connection.transmit(LOAD_KEY)
temp = LOAD_KEY
x= temp[3]
for j in range(0,len(LOAD_KEY)):
LOAD_KEY[j]=hex(LOAD_KEY[j])
print ' >>>',' Load Command :',
for j in range(0,len(LOAD_KEY)):
LOAD_KEY[j]=str(LOAD_KEY[j])
if len(LOAD_KEY[j])==3:
LOAD_KEY[j]=LOAD_KEY[j][0:2]+'0'+LOAD_KEY[j][2]
print LOAD_KEY[j],
print
for j in range(0,len(data)):
data[j]=hex(data[j])
print ' <<<',' Data :',
for j in range(0,len(data)):
data[j]=str(data[j])
if len(data[j])==3:
data[j]=data[j][0:2]+'0'+data[j][2]
print data[j],
print '--',hex(sw1),hex(sw2)
if (temp[2] == 0x00 or temp[2] == 0x20):
keyType = 0x60
else:
keyType = 0x61
AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType,temp[3]]
print 'AUTH Command: ', AUTH
data,sw1,sw2 =connection.transmit(AUTH)
print data, sw1, sw2
And its output :
Auth Command: [255, 134, 0, 0, 5, 1, 0, 4, 97, '0x0e']
Traceback (most recent call last):
File "C:\Users\Erb4h1m\Desktop\Faraadis Alborz Card Reader\CRT-603-CZ1_Read1Block.py", line 199, in <module>
data,sw1,sw2 =connection.transmit(AUTH)
File "D:\Software\Python27\lib\site-packages\smartcard\CardConnectionDecorator.py", line 82, in transmit
return self.component.transmit(bytes, protocol)
File "D:\Software\Python27\lib\site-packages\smartcard\CardConnection.py", line 140, in transmit
data, sw1, sw2 = self.doTransmit(bytes, protocol)
File "D:\Software\Python27\lib\site-packages\smartcard\pcsc\PCSCCardConnection.py", line 173, in doTransmit
hresult, response = SCardTransmit(self.hcard, pcscprotocolheader, bytes)
File "D:\Software\Python27\lib\site-packages\smartcard\scard\scard.py", line 1329, in SCardTransmit
return _scard.SCardTransmit(*args)
TypeError: Expected a list of bytes.
And when I replace temp[3] with x:
for LOAD_KEY in validLoadCommands:
data,sw1,sw2 =connection.transmit(LOAD_KEY)
temp = LOAD_KEY
x= temp[3]
for j in range(0,len(LOAD_KEY)):
LOAD_KEY[j]=hex(LOAD_KEY[j])
print ' >>>',' Load Command :',
for j in range(0,len(LOAD_KEY)):
LOAD_KEY[j]=str(LOAD_KEY[j])
if len(LOAD_KEY[j])==3:
LOAD_KEY[j]=LOAD_KEY[j][0:2]+'0'+LOAD_KEY[j][2]
print LOAD_KEY[j],
print
for j in range(0,len(data)):
data[j]=hex(data[j])
print ' <<<',' Data :',
for j in range(0,len(data)):
data[j]=str(data[j])
if len(data[j])==3:
data[j]=data[j][0:2]+'0'+data[j][2]
print data[j],
print '--',hex(sw1),hex(sw2)
if (temp[2] == 0x00 or temp[2] == 0x20):
keyType = 0x60
else:
keyType = 0x61
AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType, x]
print 'AUTH Command: ', AUTH
data,sw1,sw2 =connection.transmit(AUTH)
print data, sw1, sw2
Then the output is:
AUTH: [255, 134, 0, 0, 5, 1, 0, 4, 97, 14]
[] 144 0
As you see above, in the second case I DON'T receive any error, while there is no difference between first program and second program! I only replaced
AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType,temp[3]]
with:
AUTH = [0xFF, 0x86, 0x00, 0x00, 0x05, 0x01, 0x00, blockNum, keyType,x]
and x is initialized with temp[3] in the top of program. neither x nor temp[3] didn't changed between the line of initialization and the line of error.
What is going here?
Your temp variable reference LOAD_KEY (Line 3: temp = LOAD_KEY)
When x= temp[3] get called, it's the value of LOAD_KEY at index 3 right after your connection.transmit that is set.
When you are sending temp[3] for your AUTH, LOAD_KEY have changed and so does temp[3]. So it's not anymore the same value as x.
connection.transmit => LOAD_KEY is set => temp => [3] => x
*** LOAD_KEY changes ***
x => old value of temp[3] aka LOAD_KEY[3]
temp[3] => whatever your code have put in it
Edit: short example
>>> LOAD_KEY = ['one', 'two', 'three', 'four']
>>> temp = LOAD_KEY
>>> x = temp[3]
>>> LOAD_KEY[3] = 'new value'
>>>
>>> LOAD_KEY[3]
'new value'
>>> temp[3]
'new value'
>>> x
'four'
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