Encode the alphabet cipher
05AB1E, 11 6 bytes

Code:

Ç4+€¦J


Explanation:

First, we convert the string to their ASCII values. codegolf would become:

[99, 111, 100, 101, 103, 111, 108, 102]


To get to the indices of the alphabet, you subtract 96:

[3, 15, 4, 5, 7, 15, 12, 6]


To pad with zeros, add 100 to each element and remove the first character of each int. For the above example, +100 would be:

[103, 115, 104, 105, 107, 115, 112, 106]


And removing the first character of each would lead to:

[03, 15, 04, 05, 07, 15, 12, 06] 


We can merge both steps above (the -96 and the +100) part to just +4. For the code:

Ç       # Convert to an array of ASCII code points
 4+     # Add four to each element in the array
   €¦   # Remove the first character of each element
     J  # Join to a single string


Try it online!