102 lines
3.0 KiB
Ada
102 lines
3.0 KiB
Ada
with Ada.Text_IO; use Ada.Text_IO;
|
|
|
|
procedure chao_slices is
|
|
type iMode is (Encrypt, Decrypt);
|
|
|
|
L_Alphabet : String := "HXUCZVAMDSLKPEFJRIGTWOBNYQ";
|
|
R_Alphabet : String := "PTLNBQDEOYSFAVZKGJRIHWXUMC";
|
|
plaintext : String := "WELLDONEISBETTERTHANWELLSAID";
|
|
ciphertext : String (1 .. plaintext'length);
|
|
plaintext2 : String (1 .. plaintext'length);
|
|
offset : Natural;
|
|
|
|
function IndexOf (Source : String; Value : Character) return Positive is
|
|
Result : Positive;
|
|
|
|
begin
|
|
for I in Source'Range loop
|
|
if Source (I) = Value then
|
|
Result := I;
|
|
exit;
|
|
end if;
|
|
end loop;
|
|
return Result;
|
|
end IndexOf;
|
|
|
|
function Exec
|
|
(Text : String; mode : iMode; showsteps : Boolean := False) return String
|
|
is
|
|
etext : String (Text'First .. Text'Last);
|
|
temp : String (1 .. 26);
|
|
index : Positive;
|
|
store : Character;
|
|
left : String := L_Alphabet;
|
|
right : String := R_Alphabet;
|
|
begin
|
|
for I in Text'Range loop
|
|
if showsteps then
|
|
Put_Line (left & " " & right);
|
|
end if;
|
|
|
|
if mode = Encrypt then
|
|
index := IndexOf (Source => right, Value => Text (I));
|
|
etext (I) := left (index);
|
|
else
|
|
index := IndexOf (Source => left, Value => Text (I));
|
|
etext (I) := right (index);
|
|
end if;
|
|
|
|
exit when I = Text'Last;
|
|
|
|
-- permute left
|
|
-- The array value permutations are performed using array slices
|
|
-- rather than explicit loops
|
|
|
|
if index > 1 then
|
|
offset := 26 - index;
|
|
temp (1 .. offset + 1) := left (index .. index + offset);
|
|
|
|
temp (offset + 2 .. 26) := left (1 .. index - 1);
|
|
store := temp (2);
|
|
|
|
temp (2 .. 13) := temp (3 .. 14);
|
|
temp (14) := store;
|
|
left := temp;
|
|
|
|
-- permute right
|
|
-- The array value permutations are performed using array slices
|
|
-- rather than explicit loops
|
|
|
|
temp (1 .. offset + 1) := right (index .. index + offset);
|
|
|
|
temp (offset + 2 .. 26) := right (1 .. index - 1);
|
|
store := temp (1);
|
|
|
|
temp (1 .. 25) := temp (2 .. 26);
|
|
temp (26) := store;
|
|
store := temp (3);
|
|
|
|
temp (3 .. 13) := temp (4 .. 14);
|
|
temp (14) := store;
|
|
right := temp;
|
|
end if;
|
|
|
|
end loop;
|
|
|
|
return etext;
|
|
|
|
end Exec;
|
|
begin
|
|
Put_Line ("The original text is : " & plaintext);
|
|
New_Line;
|
|
Put_Line
|
|
("The left and right alphabets after each permutation during encryption are:");
|
|
New_Line;
|
|
ciphertext := Exec (plaintext, Encrypt, True);
|
|
New_Line;
|
|
Put_Line ("The ciphertext is : " & ciphertext);
|
|
plaintext2 := Exec (ciphertext, Decrypt);
|
|
New_Line;
|
|
Put_Line ("The recovered plaintext is : " & plaintext2);
|
|
end chao_slices;
|