ANSI X9.9 Cryptography Standards I'm trying to create a ISO8583 Rev93 message.
What is the standard way of generating MAC key in ANSI X9.9
DES-CBC encryption algorithm is used to encrypt the message and generate the MAC.  


How many bytes should I take from the encrypted byte array based on ANSI X9.9 standard? 8 or 16? I think I should take 4 bytes (8 ASCII characters) and place them on field 128 (MAC). But very doubtful about that.  
The MAC key that the customer has provided me is 16 characters. (like 1234567890123456). Should I convert it to an 8 byte key? or a 16 byte key? (Based on ISO8583 Rev93 and ANSI X9.9)


Thank you.
without doing your homework for you: did you check the open-source implementations of ISO 8583? is the answer somewhere in there?


DL-ISO-8583, in C
jPOS ISO-8583 Framework, in Java
j8583, also Java
PHP ISO-8583 Parser


Retrieved from wikipedia (strangely, the Spanish page, a good tip for finding more external references is changing the language tab)