with(linalg):

letter := proc(n)
          local alph, i, ans;
          alph := `ABCDEFGHIJKLMNOPQRSTUVWXYZ`;
          i := (n - 1 mod 26) + 1;
          ans := substring(alph,i..i);
          RETURN(ans);
end:

numbers := proc(s)           local alph, v, n, m, i, c;
alph:=`abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ`;
           n := length(s);
           v := [];
           for i from 1 to n do
               c := substring(s,i..i);
               m := searchtext(c, alph);
               if m > 0 then
                  v := [op(v), (m-1 mod 26) + 1] fi;
           od;
           RETURN(v)
end:

numbers2 := proc(s)
           local alph, v, n, m, i, c;
alph:=`abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ`;
           n := length(s);
           v := [];
           for i from 1 to n do
               c := substring(s,i..i);
               m := searchtext(c, alph);
               if m > 0 then
                  v := op(v), (m-1 mod 26) + 1 fi;
           od;
           RETURN(v)
end:

pvalues := proc(s)           local alph, v, n, m, i, j, k, c, nby2, t;
alph := `abcdefghijklmnopqrstuvwxyABCDEFGHIJKLMNOPQRSTUVWXYZ`;
           n := length(s); t := s;
           if (n mod 2 = 0) then nby2 := iquo(n,2) else                                  nby2 := iquo(n,2)+1 fi;  
           v := array(1..2,1..nby2);
           if (n mod 2 = 1) then t := cat(s,`x`) fi; 
           for i from 1 to nby2 do
               j := 2*i-1; k := j+1;
               c := substring(t,j..j);
               m := searchtext(c, alph);
               if m>0 then m:=(m-1 mod 26)+1 fi;
               v[1,i] := m;
               c := substring(t,k..k);
               m := searchtext(c, alph);
               if m>0 then m:=(m-1 mod 26)+1 fi;
               v[2,i] := m;
           od;
           RETURN(v);
  end:
out := evalm(pvalues(`helloworld`)):

C:=map(letter, out):



clock26 := x -> ((x-1) mod 26) + 1:

matmult := proc(decvec, key, keysize)
local l1, l3, i, j, k, temp, temp2, temp3;
temp2 := linalg[vector](keysize);
temp := convert(decvec,array);
l1 :=linalg[vectdim](temp);
l3 := l1/keysize;
for j from 0 to (l3 -1) do
   for i from 1 to keysize do
     temp2[i] := temp[j*keysize+i]:
   od;
   temp2 := map(clock26,linalg[multiply](key,temp2)):
   for i from 1 to keysize do
     temp[j*keysize + i] := temp2[i]:      
   od:
od;
convert(temp,list);
end:

C:=matmult(numbers(`helloworld`),E,2):


Cipher:=map(letter,C):



d:=map(numbers2,Cipher):



map(letter,d):


invertmod:= A -> map(clock26, inverse(A)):