Rainer Mattes

Undetectable Manipulation of CRC Checksums for Communication and Data Storage

The Cyclic Redundancy Check (CRC) is an efficient and widespread coding method to detect random errors in industrial and business data transmission. Because of its simple implementation and low residual error probability, it is also ap plied to data stored in digital memory. If no error occurred then the checksum (FCS, Frame Check Sequence) is consistent to the original data. Additionally, the actual value of the FCS is often used as a crite rion for e.g. the correct ver sion of the software in digital memories or to detect its manipulation. Although it is well known that data protected by CRC can be manipulated undetectably, CRC is applied for the detection of manipulations but not random errors. The paper demonstrates and proves in detail how easily data, like business software or video streams, can be manipulated such that the manipulation is not detectable even for CRC of high order.