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247 | --
-- Minimal steganography tool.
--
-- This demo is derived from mini.adb.
--
-- To do:
-- - encryption
with GID;
with Ada.Calendar;
with Ada.Characters.Handling; use Ada.Characters.Handling;
with Ada.Command_Line; use Ada.Command_Line;
with Ada.Numerics.Elementary_Functions; use Ada.Numerics.Elementary_Functions;
with Ada.Streams.Stream_IO; use Ada.Streams.Stream_IO;
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Unchecked_Deallocation;
with Interfaces;
procedure Steg is
procedure Blurb is
begin
Put_Line (Standard_Error, "Steg * Minimal steganography tool");
New_Line (Standard_Error);
Put_Line (Standard_Error, " Encoding: converts any image file to a PPM image file, with");
Put_Line (Standard_Error, " inclusion of a hidden data file. The PPM image can then");
Put_Line (Standard_Error, " be converted to a lossless-compressed format like PNG.");
New_Line (Standard_Error);
Put_Line (Standard_Error, " Decoding: extracts a hidden file from an image.");
New_Line (Standard_Error);
Put_Line (Standard_Error, "GID version " & GID.version & " dated " & GID.reference);
Put_Line (Standard_Error, "URL: " & GID.web);
New_Line (Standard_Error);
Put_Line (Standard_Error, "Syntax:");
Put_Line (Standard_Error, " steg [e|d] <image> <file>");
New_Line (Standard_Error);
end Blurb;
use Interfaces;
type Byte_Array is array (Integer range <>) of Unsigned_8;
type p_Byte_Array is access Byte_Array;
procedure Dispose is new Ada.Unchecked_Deallocation (Byte_Array, p_Byte_Array);
img_buf : p_Byte_Array := null;
-- Load image into a 24-bit truecolor RGB raw bitmap (for a PPM output)
procedure Load_raw_image (
image : in out GID.Image_descriptor;
buffer : in out p_Byte_Array;
next_frame : out Ada.Calendar.Day_Duration
)
is
subtype Primary_color_range is Unsigned_8;
image_width : constant Positive := GID.Pixel_width (image);
image_height : constant Positive := GID.Pixel_height (image);
idx : Natural;
--
procedure Set_X_Y (x, y : Natural) is
begin
idx := 3 * (x + image_width * (image_height - 1 - y));
end Set_X_Y;
--
procedure Put_Pixel (
red, green, blue : Primary_color_range;
alpha : Primary_color_range
)
is
pragma Warnings (off, alpha); -- alpha is just ignored
begin
buffer (idx .. idx + 2) := (red, green, blue);
idx := idx + 3;
-- ^ GID requires us to look to next pixel on the right for next time.
end Put_Pixel;
stars : Natural := 0;
procedure Feedback (percents : Natural) is
so_far : constant Natural := percents / 5;
begin
for i in stars + 1 .. so_far loop
Put (Standard_Error, '*');
end loop;
stars := so_far;
end Feedback;
procedure Load_image is
new GID.Load_image_contents (
Primary_color_range, Set_X_Y,
Put_Pixel, Feedback, GID.fast
);
begin
Dispose (buffer);
buffer := new Byte_Array (0 .. 3 * image_width * image_height - 1);
Load_image (image, next_frame);
end Load_raw_image;
procedure Dump_PPM (name : String; i : GID.Image_descriptor) is
f : Ada.Streams.Stream_IO.File_Type;
ppm_name : constant String := name & ".ppm";
begin
Create (f, Out_File, ppm_name);
Put_Line (Standard_Error, "Creating PPM image, name = " & ppm_name & " ...");
-- PPM Header:
String'Write (
Stream (f),
"P6 " &
Integer'Image (GID.Pixel_width (i)) &
Integer'Image (GID.Pixel_height (i)) & " 255" & ASCII.LF
);
-- PPM raw BGR image:
Byte_Array'Write (Stream (f), img_buf.all);
-- ^ slow on some Ada systems, see to_bmp to have a faster version
Close (f);
end Dump_PPM;
type Operation is (encoding, decoding);
Data_too_large : exception;
procedure Process (image_name, data_name : String; op : Operation) is
f_im, f_dt : Ada.Streams.Stream_IO.File_Type;
--
procedure Encode is
idx : Natural := img_buf'Last;
-- Start with buffer's end (image's bottom), with the hope it is "noisier":
-- often there is a blue sky or something like that on the top...
procedure Encode_byte (b : Unsigned_8) is
begin
img_buf (idx) := (img_buf (idx) and 2#1111_1100#) or (b and 2#0000_0011#); -- B
idx := idx - 1;
img_buf (idx) := (img_buf (idx) and 2#1111_1000#) or Shift_Right (b and 2#0001_1100#, 2); -- G
idx := idx - 1;
img_buf (idx) := (img_buf (idx) and 2#1111_1000#) or Shift_Right (b, 5); -- R
idx := idx - 1;
end Encode_byte;
b : Unsigned_8;
data_size : Unsigned_64;
needed_size : Unsigned_64;
available_size : constant Unsigned_64 := img_buf'Length / 3; -- 1 byte per pixel;
factor : Float;
begin
Open (f_dt, In_File, data_name);
data_size := Unsigned_64 (Size (f_dt));
needed_size := data_size + 8;
factor := Float (needed_size) / Float (available_size);
if needed_size > available_size then
raise Data_too_large with
"Needs a" & Integer'Image (1 + Integer (100.0 * factor)) &
"% raw size scaling, i.e. a" &
Integer'Image (1 + Integer (100.0 * Sqrt (factor))) &
"% image scaling in both dimensions";
end if;
Put_Line (Standard_Error,
"Data size:" & Unsigned_64'Image (data_size) &
", using" & Integer'Image (Integer (100.0 * factor)) &
"% of image data"
);
for i in 1 .. 8 loop
Encode_byte (Unsigned_8 (data_size and 16#FF#));
data_size := Shift_Right (data_size, 8);
end loop;
while not End_Of_File (f_dt) loop
Unsigned_8'Read (Stream (f_dt), b);
Encode_byte (b);
end loop;
Close (f_dt);
end Encode;
--
procedure Decode is
idx : Natural := img_buf'Last;
procedure Decode_byte (b : out Unsigned_8) is
begin
b := img_buf (idx) and 2#0000_0011#; -- B
idx := idx - 1;
b := b + Shift_Left (img_buf (idx) and 2#0000_0111#, 2); -- G
idx := idx - 1;
b := b + Shift_Left (img_buf (idx) and 2#0000_0111#, 5); -- R
idx := idx - 1;
end Decode_byte;
b : Unsigned_8;
data_size : Unsigned_64 := 0;
begin
for i in 0 .. 7 loop
Decode_byte (b);
data_size := data_size + Shift_Left (Unsigned_64 (b), i * 8);
end loop;
Create (f_dt, Out_File, data_name);
for i in 1 .. data_size loop
Decode_byte (b);
Unsigned_8'Write (Stream (f_dt), b);
end loop;
Close (f_dt);
end Decode;
--
i : GID.Image_descriptor;
up_name : constant String := To_Upper (image_name);
--
next_frame : Ada.Calendar.Day_Duration;
begin
--
-- Load the image in its original format
--
Open (f_im, In_File, image_name);
Put_Line (Standard_Error, "Processing " & image_name & "...");
--
GID.Load_image_header (
i,
Stream (f_im).all,
try_tga =>
image_name'Length >= 4 and then
up_name (up_name'Last - 3 .. up_name'Last) = ".TGA"
);
Put_Line (Standard_Error, ".........v.........v");
--
Load_raw_image (i, img_buf, next_frame);
New_Line (Standard_Error);
Close (f_im);
case op is
when encoding =>
Encode;
Dump_PPM (image_name, i); -- Output encoded image
when decoding =>
Decode;
end case;
end Process;
op : Operation;
begin
if Argument_Count /= 3 then
Blurb;
return;
end if;
if To_Lower (Argument (1)) = "e" then
op := encoding;
elsif To_Lower (Argument (1)) = "d" then
op := decoding;
else
Blurb;
return;
end if;
Process (Argument (2), Argument (3), op);
end Steg;
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