javacard - How to understand Java Card APDU commands? -

i trying learn programming java cards. have started it. but, not finding complete e-book.

how understand apdu commands?

for example, how can understand meaning if cla = 10101010? or, if ins = 10101010?

is there intuitive guide available on net?

apdu commands queue of binary numbers in following form:

cla | ins | p1 | p2 | lc | cdata | le

the first 4 sections, i.e cla , ins , p1 , p2 mandatory in apdu commands , each 1 has 1 byte length. these one-byte-length sections stand class, instruction, parameter1 , parameter2 respectively.

the last 3 sections, i.e lc , cdata , le optional.lc encoding of nc, encoding of length of cdata field. le encoding of ne, encoding of maximum response data may send. based on presence or absence of these sections, have 4 case apdu commands, below:

• case1: cla | ins | p1 | p2
• case2: cla | ins | p1 | p2 | le
• case3: cla | ins | p1 | p2 | lc | data
• case4: cla | ins | p1 | p2 | lc | data | le

the length of cdata different different commands , different applets. based on length of cdata (i.e lc) , length of maximum response data may send (i.e le), have type of apdu commands:

• normal/short apdu commands, when lc and le smaller 0xff
• extended length apdu commands, when lc and/or le greater 0xff.

so length of these sections have:

lc : 1 byte short apdu commands , 3 byte (they specify length, because enough) extended apdu commands.

data : different lengths.

le : same lc.

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how can understand apdu commands?

answer:

when write applet, specify response of applet different apdu commands receive in future. card manager applet also. commands support defined in card's specifications/datasheet. cards globalplatform , iso7816 compliant, must support mandatory apdu commands defined in these documents. example, 0xa4 defined select file command in iso7816-4 standard, if see apdu xx a4 xx xx sending card manager, can conclude related select file.

note can choose 1 value different functions in different applets. example in following, applet1 return 0x6990 in reception of 00 b0 xx xx apdu commands, while applet2 return 0x6991 in reception of same command:

applet1:

public class soq extends applet {      private soq() {     }      public static void install(byte barray[], short boffset, byte blength)             throws isoexception {         new soq().register();     }      public void process(apdu arg0) throws isoexception {         byte buffer[] = arg0.getbuffer();          if(buffer[iso7816.offset_cla]==0x00 && buffer[iso7816.offset_ins]==0xb0){             isoexception.throwit((short)0x6990);         }      }  } 

output:

opensc: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00b00000 -s 00b00 100 using reader card: acs ccid usb reader 0 sending: 00 a4 04 00 0b 01 02 03 04 05 06 07 08 09 00 00 received (sw1=0x90, sw2=0x90) sending: 00 b0 00 00 received (sw1=0x69, sw2=0x90) sending: 00 b0 01 00 received (sw1=0x69, sw2=0x90) 

applet2:

public class soq extends applet {      private soq() {     }      public static void install(byte barray[], short boffset, byte blength)             throws isoexception {         new soq().register();     }      public void process(apdu arg0) throws isoexception {         byte buffer[] = arg0.getbuffer();          if(buffer[iso7816.offset_cla]==0x00 && buffer[iso7816.offset_ins]==0xb0){             isoexception.throwit((short)0x6991);         }      }  } 

output:

opensc: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00b00000 -s 00b00 100 using reader card: acs ccid usb reader 0 sending: 00 a4 04 00 0b 01 02 03 04 05 06 07 08 09 00 00 received (sw1=0x90, sw2=0x00) sending: 00 b0 00 00 received (sw1=0x69, sw2=0x91) sending: 00 b0 01 00 received (sw1=0x69, sw2=0x91) 

so final , short answer question (how can understand apdu commands?) is:

• you dealing applet?

  you defined supported commands , forms, yourself!

• you dealing applet (card manager, example)?

  you need source code of applet or documentation supported commands , forms or standard/specification that applet compliant (global platform card managers example).

note: have same apdu responses.