Reversing CRC - Theory and Practice

The Cyclic Redundancy Check (CRC) was developed as a checksum algorithm for the detection of data corruption in the process of datatransmission or storage. However, in some scenarios there's a CRC given which a set of data is expected to have, so the data itself has to be modified (at the end or at some chosen position) in away that it computes to the given CRC checksum afterwards. We present methods providing solutions to this problem. Each algorithm is explained in theory and accompanied by an implementation for the CRC32 in the C programming language.