Possibility of Overlapping
A few words about the issue of returning the input file as the output in an encryption algorithm... 1. Algorithm as a black box If we think of any encryption algorithm, irrespective of its content, like a black box, we can accept the encryption process as an injective mapping from the input file to the output file. If we consider that both plain and chiper alphabets are B = {0, 1}, we can write E k : B n ® B n for our E k encryption function. n is the word or block length that is determined by the selected algorithm. The point to be emphasized here is: It’s not important at all that E k function forms a Fiestel- or a SP-network, or it’s a stream chipher or represents another encryption method. It’s enough that it just doesn’t contain extension, that means the length of the input file is equivalent to the length of the output file. Moreover, a little detailing would suff...