Does this algorithm have a name? (Distance between letters) This came to mind the other day and I'm wanting to know if there is a name for the following algorithm (I'm not sure if &quot;cipher&quot; is the right word for it):

Take two consecutive letters at a time (not just one).
Perform the A1Z26 cipher on each letter to get their position in the alphabet as numbers.
Take the difference between those numbers obtained in the previous step.
Convert the difference back into a letter through A1Z26 in reverse. If the difference is positive, use a capital letter. If the difference is negative, use a lowercase letter. If you encounter two of the same letter in a row (difference is 0), convert them to the letter Z, since there is no &quot;0th&quot; letter of the alphabet, and Z would otherwise go unused since we're taking differences (the maximum difference possible would be Z - A -&gt; 26 - 1 = 25 -&gt; Y). Z is always capitalized.
Repeat until you reach the last letter, in which case you &quot;wrap&quot; back around from the last letter to the first.

&quot;Hello world&quot;, for example, becomes &quot;CgZcG HcFHs&quot;

H, e -&gt; 8 - 5 = 3 -&gt; C
e, l -&gt; 5 - 12 = -7 -&gt; g
l, l -&gt; 12 - 12 = 0 -&gt; Z
l, o -&gt; 12 - 15 = -3 -&gt; c
o, H -&gt; 15 - 8 = 7 -&gt; G
w, o -&gt; 23 - 15 = 8 -&gt; H
o, r -&gt; 15 - 18 = -3 -&gt; c
r, l -&gt; 18 - 12 = 6 -&gt; F
l, d -&gt; 12 - 4 = 8 -&gt; H
d, W -&gt; 4 - 23 = -19 -&gt; s

Is there a name for this method, or a similar algorithm? What are other examples of algorithms working on not the individual letters themselves, but mathematical operations between 2+ letters?
This answer is expanding on @mentallurg's comment.
One of the important properties of a cipher is that you can decrypt. More precisely that there is an algorithm that takes in the cipher text and the private key and produces the correct plaintext. (Your scheme does not have a key, which is a separate problem with calling it a cipher).
So let's take your ciphertext &quot;CgZcG HcFHs&quot; and try decrypting it.
C = 3
g = -7
Z = 0
c = -3
G = 7
 
H = 8
c = -3
F = 6
H = 8
s = -19

So I know the distance between the fist and second letter is 3, but I don't know what the first letter actually is. If I knew the first letter then the rest would be uniquely determined. If your alphabet is [a-zA-Z] then there are 52 different plaintexts that would have produced this ciphertext, and the decryption algorithm has no way to know which of the 52 was the intended plaintext.