DES: histogram differences between plaintext and ciphertext Using CrypTool I encrypted a plaintext with "DES CBC" and I genereated the histogram of plaintext and ciphertext.
The histogram shows the relative frequency of each of the characters in the document.

When I did the same with "Caesar" cipher based on online tutorials, it was possible to find the correlation between some characters comparing their frequency that I could see in their histograms.

But that it is not possible for DES. I try to find out why this is not possible. What properties of the DES are responsible for this?
Lookup avalanche effect either in wiki or our tags here. Essentially, the slightest change (any single bit) of the plain text leads to 50% of all the other bits (on average) changing across the full width of DES' 64 bit block size.  This totally obfuscates any correlation between the plain text characters.

"Caesar" cipher doesn't exhibit avalanche being only a substitution. It simply keeps the correlations and encodes them to other letters.