Generate a matrix with all allowed pairs of letters, reshape it and base-64 encode it. The base-64 encoded string ('CR+ ... % ') is used as data in the program. The program reverses operations and reads the combinations:
x=de2bi('CR+"''        1$$L*\"%!! ! !04P@100@RZP4  $$0 ! 1$$1 0  P (    $0 0$ ! # %  '-32)';[i,j]=find(reshape(x(1:650),26,[])');char([j i]+64)