a device and a method for forming a signature , a predefined number of shift registers being provided , to which input data to be tested is applied bit - by - bit and in parallel as successive data words and which serially shift the input data forward in a predefinable cycle , a signature being formed in the shift registers after a certain number of data words and cycles , a code generator which generates at least one additional bit position in at least one additional shift register from each data word in the signature also being provided .