generate AC cryptogram manually

Question

I am trying to generate AC manually, I have a tool to generate AC but I want to generate it by my own to understand the algorithm for the same.

My calculation is fine fo

Answer 1

MasterCard Application Cryptogram (AC) generation is more complicated than other card schemes.

1. Card can use different ICC Session Key Derivation (SKD) methods:

   • MasterCard Proprietary SKD, where involved Application Transaction Counter (ATC) and Unpredictable Number (UN);
   • EMV2000 Method, where involved only ATC - see EMV 4.0, Book 2;
   • EMV Common Session Key (CSK) Method, where involved only ATC - see EMV 4.2, Book 2;

2. Data Objects (DO) can be with different sets of additional or modified values:

   • Card Verification Results (CVR) can be 6 or 4 bytes.
   • The offline counters from Issuer Application Data (IAD) can be included.
   • Last online ATC value can be included.

The used method and data variant can be detected by Cryptogram Version Number (CVN) and Application Control bits. CVN is sub-field of IAD tag 0x9F10 .

The detailed information are proprietary and available for the MasterCard members.

For deep learning about it take a look into "M/Chip Card Application Cryptographic Algorithms" and M/Chip Card Application references.