Comparing Ciphertext when there is a change in source plaintext p1 So, i know that if there is a change in source plaintext p1, c1 and rest of cipher blocks will be affected as c is required for the calculation in cfb. What i need to know is that how can i show how many blocks will be affected when there is this error. I have tried comparing the two cipher texts(one with no change in p1, and one with a bit change in p1) using diff, but i've had no luck in showing how many blocks are affected with the change in p1. Thanks.
i don't think that there is a way to check the changes on block cipher if you are using random IV here, since the IV will go to Enc first, then the output would be totally different than before, 

if you are using the same IV, then try to figure out the the block length for the block you are using, if it is 16 bytes, then change the first 16 bytes will result first 16 bytes of ciphertext to be different. Since before output the ciphertext, it is just a one-time pad. 

hope it helps.