The question is quite similar to this one : Forge CBC-MAC given the MAC of two messages and of their concatenation
But i still cannot fully understand it, and here's my question:
giving two messages with known MAC:
So from the given message, i am able to forge a new message like this:
CBC-MAC(a || b || (d XOR x) || e ) = y which just like the post i read.
But how about if i want to forge the message like this:
CBC-MAC(a || b || c || d || e ) = z
The "c" maybe something calculated from those two message and its MAC, I am not sure about it.
Is it possible to achieve this?