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I'm going to make a long story short. It's been a while that I want to implement my own AES encryption/decryption program. The encryption program went well and encrypting without any error or strange output (Since I have compared my program's output with a working commercial one and result was the same). Wikipedia was (is) my guide in this implementation within which I read "A set of reverse rounds are applied to transform ciphertext back into the original plaintext using the same encryption key." There are couple of modules that I implemented: Add round key Shift rows Sub bytes Mix Column I also implemented couple of reverse implementation of the above modules: Reverse shift rows Reverse Sub Byte Reverse Mix Column NOTE: I didn't implement reverse round key since, It's XOR ing the plaintext with the encryption key, and reverse of XOR is XOR itself (correct me if I am wrong) So I putted this modules in the reverse order that I did encryption, but never I got my plain-text back: expandkey128(key); rev_subbytes(data); rev_shiftrows(data); addroundkey(data,key,10); for(int i = 9; i>= 1; i--) { rev_subbytes(data); rev_shiftrows(data); rev_mixColum(data); addroundkey(data,key,i); } addroundkey(data,key,0); // Please note that I also did from 0 to 10 , // instead of 10 to 0 and didn't workout And also I thought , maybe I should not implement reverse model of the modules, maybe I have to use those modules that I did encryption with, only in reverse order; well guess what? didn't work! : expandkey128(key); addroundkey(data,key,0); for(int i = 1; i<= 9; i++) { subbytes(data); shiftrows(data); mixColum(data); addroundkey(data,key,i); } subbytes(data); shiftrows(data); addroundkey(data,key,10); So here is the question: what is wrong? |

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