VBA Crypto solving

[spacker15]

I am trying to solve some simple crypto, that looks something like this;

cells 1,1 has the alphabet and cells 1,2 has the key.
a = z
b = y
c = x

this is my long drawn out code for 1 cell.

If Cells(1, 3) = "A" Then
    Cells(1, 3) = Cells(1, 2)
ElseIf Cells(1, 3) = "B" Then
    Cells(1, 3) = Cells(2, 2)
ElseIf Cells(1, 3) = "C" Then
    Cells(1, 3) = Cells(3, 2)

ect...

is there an easier way? please help.

Thank you,

Sean