Compute the Redwolf Checksum™ of some data
K (ngn/k), 84 67 bytes
-17 bytes by reshuffling things, inspired by @Neil's comment.
{(,/($!10),`c$97+!26)36!+/256 32 2!'2(,/|0 1_)\+/-1_(0N;y)#x,0,y#0}

Try it online!

+/-1_(0N;y)#x,0,y#0 take the column-wise sum of the input split into y-length chunks (filling with 0s)
2(,/|0 1_)\ build a list containing the original input, it rotated once, and it rotated twice (this uses the do overload of \ scan)
256 32 2!' mod the original input by 256, the rotated-once input by 32, and the rotated-twice input by 2
36!+/ sum column-wise, modding by 36
(,/($!10),`c$97+!26) build list of base-36 characters (digits followed by lower case letters), which is indexed into by the results of the above