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191 | -- --
-- package Copyright (c) Dmitry A. Kazakov --
-- Strings_Edit.Symmetric_Serialization Luebeck --
-- Implementation Winter, 2008 --
-- --
-- Last revision : 22:45 07 Apr 2016 --
-- --
-- This library is free software; you can redistribute it and/or --
-- modify it under the terms of the GNU General Public License as --
-- published by the Free Software Foundation; either version 2 of --
-- the License, or (at your option) any later version. This library --
-- is distributed in the hope that it will be useful, but WITHOUT --
-- ANY WARRANTY; without even the implied warranty of --
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU --
-- General Public License for more details. You should have --
-- received a copy of the GNU General Public License along with --
-- this library; if not, write to the Free Software Foundation, --
-- Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from --
-- this unit, or you link this unit with other files to produce an --
-- executable, this unit does not by itself cause the resulting --
-- executable to be covered by the GNU General Public License. This --
-- exception does not however invalidate any other reasons why the --
-- executable file might be covered by the GNU Public License. --
--____________________________________________________________________--
with Ada.IO_Exceptions; use Ada.IO_Exceptions;
with Interfaces; use Interfaces;
with Ada.Numerics.Discrete_Random;
with Generic_Random_Sequence;
package body Strings_Edit.Symmetric_Serialization is
type Octet is new Interfaces.Unsigned_8;
--
-- Random_Octet -- Pseudo-random generator of blocks
--
package Random_Octet is
new Ada.Numerics.Discrete_Random (Octet);
use Random_Octet;
--
-- Octet_Sequence - A sequence of octets
--
package Octet_Sequence is new Generic_Random_Sequence (Octet);
use Octet_Sequence;
Seed_Init : constant := 71;
Carry_Init : constant := 37;
Bit_Mask : constant array (0..8) of Unsigned_16 :=
( 2#0000_0000#, 2#0000_0001#, 2#0000_0011#,
2#0000_0111#, 2#0000_1111#, 2#0001_1111#,
2#0011_1111#, 2#0111_1111#, 2#1111_1111#
);
Encoding : constant array (Unsigned_16 range 0..63) of Character :=
( "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
& "abcdefghijklmnopqrstuvwxyz"
& "0123456789_~"
);
Decoding : constant array (Character) of Octet :=
( 'A'=> 0, 'B'=> 1, 'C'=> 2, 'D'=> 3, 'E'=> 4,
'F'=> 5, 'G'=> 6, 'H'=> 7, 'I'=> 8, 'J'=> 9,
'K'=>10, 'L'=>11, 'M'=>12, 'N'=>13, 'O'=>14,
'P'=>15, 'Q'=>16, 'R'=>17, 'S'=>18, 'T'=>19,
'U'=>20, 'V'=>21, 'W'=>22, 'X'=>23, 'Y'=>24,
'Z'=>25, 'a'=>26, 'b'=>27, 'c'=>28, 'd'=>29,
'e'=>30, 'f'=>31, 'g'=>32, 'h'=>33, 'i'=>34,
'j'=>35, 'k'=>36, 'l'=>37, 'm'=>38, 'n'=>39,
'o'=>40, 'p'=>41, 'q'=>42, 'r'=>43, 's'=>44,
't'=>45, 'u'=>46, 'v'=>47, 'w'=>48, 'x'=>49,
'y'=>50, 'z'=>51, '0'=>52, '1'=>53, '2'=>54,
'3'=>55, '4'=>56, '5'=>57, '6'=>58, '7'=>59,
'8'=>60, '9'=>61, '_'=>62, '~'=>63,
others =>64
);
procedure Adjust
( Dice : Generator;
Key : String;
Pointer : in out Integer;
Seed : in out Integer
) is
begin
if Pointer > Key'First then
Pointer := Pointer - 1;
else
Pointer := Key'Last;
end if;
Seed := Seed + Character'Pos (Key (Pointer));
Reset (Dice, Seed);
end Adjust;
function Decode (Data : Encoded_String; Key : String)
return String is
Sequencer : Sequence;
Dice : Generator;
Result : String (1..256);
Value : Octet := Carry_Init;
Accum : Unsigned_16 := 0;
Bits : Natural := 0;
Position : Integer := 0;
Key_Index : Integer := Key'First;
Seed : Integer := Seed_Init;
begin
for Pointer in Data'Range loop
declare
Code : constant Octet := Decoding (Data (Pointer));
begin
if Code > 63 then
raise Data_Error;
end if;
Accum := Shift_Left (Accum, 6) + Unsigned_16 (Code);
end;
Bits := Bits + 6;
if Bits >= 8 then
Adjust (Dice, Key, Key_Index, Seed);
Next (Sequencer, Random (Dice) xor Value, Octet (Position));
Position := Position + 1;
Bits := Bits - 8;
Value := Octet (Shift_Right (Accum, Bits));
Result (Position) := Character'Val (Value xor Random (Dice));
Accum := Accum and Bit_Mask (Bits);
if Length (Sequencer) = 0 then
if Pointer /= Data'Last then
raise Data_Error;
end if;
return Result;
end if;
end if;
end loop;
raise Data_Error;
end Decode;
function Encode (Text : String; Key : String)
return Encoded_String is
Sequencer : Sequence;
Dice : Generator;
Result : Encoded_String;
Data : array (Octet) of Octet;
Value : Octet := Carry_Init;
Accum : Unsigned_16 := 0;
Bits : Natural := 0;
Pointer : Integer := Result'First;
Key_Index : Integer := Key'First;
Seed : Integer := Seed_Init;
begin
if Text'Length > 256 then
raise Constraint_Error;
end if;
-- Copying text
for Index in Text'Range loop
Data (Octet (Index - Text'First)) :=
Character'Pos (Text (Index));
end loop;
if Text'Length < Data'Length then
-- Padding to block size with some random stuff
for Index in Text'Length..Data'Last loop
Data (Index) := Random (Dice);
end loop;
end if;
for Index in Data'Range loop
Adjust (Dice, Key, Key_Index, Seed);
Value := Data (Next (Sequencer, Random (Dice) xor Value));
Value := Value xor Random (Dice);
Accum := Shift_Left (Accum, 8) + Unsigned_16 (Value);
Bits := Bits + 8;
if Bits >= 6 then
if Bits >= 12 then
Bits := Bits - 6;
Result (Pointer) := Encoding (Shift_Right (Accum, Bits));
Pointer := Pointer + 1;
Bits := Bits - 6;
Result (Pointer) :=
Encoding (Shift_Right (Accum, Bits) and 2#11_1111#);
else
Bits := Bits - 6;
Result (Pointer) := Encoding (Shift_Right (Accum, Bits));
end if;
Pointer := Pointer + 1;
Accum := Accum and Bit_Mask (Bits);
end if;
end loop;
if Bits > 0 then
Result (Pointer) := Encoding (Shift_Left (Accum, 6 - Bits));
Pointer := Pointer + 1;
end if;
return Result (1..Pointer - 1);
end Encode;
end Strings_Edit.Symmetric_Serialization;
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