I got a great comment on my post regarding simple binary file visual analysis from Erik Heidt. Erik made the very valid point that visual analysis of ciphertext is not a highly reliable way to distinguish "good" crypto from "bad." He used the example of an 8-bit XOR of a file as an ineffective method of encrypting data that also has random byte distribution.
Since there's nothing good on TV, I decided to see what an XOR-ed file data looks like in gnuplot. So here's what I did.
Like before, I used the Netcat nc.exe binary. I then encrypted it using GPG and also encoded it using Luigi Auriemma's Xor utility. I then ran the three files through the Perl script from my previous post and then plotted them with gnuplot.
Here's the plot of the original binary:
Here's the plot of the GPG-encrypted file:
And here's the plot of the XOR-encoded file:
As you can see, the XOR plot has peaks and valleys that are characteristically similar to the original binary. I don't want you to take away from this that this visual analysis method is highly reliable in all situations. I only wanted to share that basic XOR encoding does stand out visually.