I hope someone can help me with this.

I have a column of "encrypted" data (in excel), which needs to be converted.
The data in each cell is "encrypted" by following this simple rule:

A = 1
B = 2
C = 3
D = 4
E = 5
F = 6
G = 7
H = 8
I = 9
J =0

Therefore, if a cell has "BFDJ", the numerical value will be 2640.

My problem is this:

How can I take the sum of the "encrypted" data in the column to make a grand
total, which is also encrypted using the above rule?

I've looked around and it seems that there are functions which can change
numbers into words, but not the other way round.

Any assistance is much appreciated.