Apakah yang dimaksud dengan steganografi??

Steganografi merupakan suatu teknik menyembunyikan sebuah file pada file lainnya. Dalam metode ini diperlukan file sebagai penampung (cover) dan file lain yang akan ditampung (message). File penampung maupun file yang akan ditampung dapat berupa citra, audio, maupun text.

Penggunaan steganografi bertujuan untuk menyembunyikan atau menyamarkan suatu data sehingga sulit untuk dideteksi (encoding). Data yang disembunyikan dapat diekstraksi kembali sama seperti keadaan aslinya (decoding).

Berikut ini merupakan contoh pemrograman matlab mengenai steganografi dengan metode substitusi LSB (Least Significant Bit) di mana baik file penampung maupun file yang akan ditampung adalah berupa citra digital.

Langkah-langkah pemrogramannya adalah sebagai berikut:

1. Pembuatan GUI Encoding Citra

function varargout = proses_encoding(varargin)
% PROSES_ENCODING MATLAB code for proses_encoding.fig
%      PROSES_ENCODING, by itself, creates a new PROSES_ENCODING or raises the existing
%      singleton*.
%
%      H = PROSES_ENCODING returns the handle to a new PROSES_ENCODING or the handle to
%      the existing singleton*.
%
%      PROSES_ENCODING('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in PROSES_ENCODING.M with the given input arguments.
%
%      PROSES_ENCODING('Property','Value',...) creates a new PROSES_ENCODING or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before proses_encoding_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to proses_encoding_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help proses_encoding

% Last Modified by GUIDE v2.5 02-Jan-2019 08:49:25

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
    'gui_Singleton',  gui_Singleton, ...
    'gui_OpeningFcn', @proses_encoding_OpeningFcn, ...
    'gui_OutputFcn',  @proses_encoding_OutputFcn, ...
    'gui_LayoutFcn',  [] , ...
    'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before proses_encoding is made visible.
function proses_encoding_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to proses_encoding (see VARARGIN)

% Choose default command line output for proses_encoding
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);
movegui(hObject,'center');

% UIWAIT makes proses_encoding wait for user response (see UIRESUME)
% uiwait(handles.figure1);


% --- Outputs from this function are returned to the command line.
function varargout = proses_encoding_OutputFcn(hObject, eventdata, handles)
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;


% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% menampilkan menu open file
[nama_file, nama_path] = uigetfile('*.bmp');
% jika ada file yang dipilih maka akan mengeksekusi perintah di bawahnya
if ~isequal(nama_file,0)
    % membaca file citra
    Img_cover = imread(fullfile(nama_path,nama_file));
    % menampilkan citra pada axes1
    axes(handles.axes1)
    imshow(Img_cover)
    title('Citra Cover')
    % menyimpan variabel Img_cover pada lokasi handles
    handles.Img_cover = Img_cover;
    guidata(hObject, handles)
else
    % jika tidak ada file yang dipilih maka akan kembali
    return
end

% --- Executes on button press in pushbutton2.
function pushbutton2_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton2 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% menampilkan menu open file
[nama_file, nama_path] = uigetfile('*.bmp');
% jika ada file yang dipilih maka akan mengeksekusi perintah di bawahnya
if ~isequal(nama_file,0)
    % membaca file citra
    Img_message = imread(fullfile(nama_path,nama_file));
    % menampilkan citra pada axes2
    axes(handles.axes2)
    imshow(Img_message)
    title('Citra Message')
    % menyimpan variabel Img_message pada lokasi handles
    handles.Img_message = Img_message;
    guidata(hObject, handles)
else
    % jika tidak ada file yang dipilih maka akan kembali
    return
end

% --- Executes on button press in pushbutton3.
function pushbutton3_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton3 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% memanggil variabel Img_cover dan Img_message yang ada di lokasi handles
Img_cover = handles.Img_cover;
Img_message = handles.Img_message;

% jika kedua citra berukuran sama maka akan mengeksekusi perintah di
% bawahnya
if isequal(size(Img_cover),size(Img_message))
    % membaca LSB bits yang ada di edit1
    n = str2double(get(handles.edit1,'String'));
    % proses steganografi dengan metode substitusi LSB
    Img_steg = uint8(bitor(bitand(Img_cover,bitcmp(2^n-1,'uint8')),...
        bitshift(Img_message,n-8)));
    % menampilkan citra hasil steganografi pada axes3
    axes(handles.axes3)
    imshow(Img_steg)
    title('Citra Steganografi')
    % menyimpan citra hasil steganografi pada lokasi handles
    handles.Img_steg = Img_steg;
    guidata(hObject, handles)
else
    % jika kedua citra berukuran tidak sama maka akan menampilkan
    % error dialog
    errordlg('Ukuran kedua citra harus sama','File Error');
end

function edit1_Callback(hObject, eventdata, handles)
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit1 as text
%        str2double(get(hObject,'String')) returns contents of edit1 as a double


% --- Executes during object creation, after setting all properties.
function edit1_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end


% --- Executes on button press in pushbutton4.
function pushbutton4_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton4 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% membaca citra hasil steganografi yang ada di lokasi handles
Img_steg = handles.Img_steg;
% menampilkan menu save file
[nama_file, nama_path] = uiputfile('*.bmp');
% jika ada file yang dipilih maka akan mengeksekusi perintah di bawahnya
if ~isequal(nama_file,0)
    % menyimpan citra hasil steganografi
    imwrite(Img_steg,fullfile(nama_path,nama_file))
else
    % jika ada file yang dipilih maka akan kembali
    return
end

% --- Executes on button press in pushbutton5.
function pushbutton5_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton5 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% mereset button2
axes(handles.axes1)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])

axes(handles.axes2)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])

axes(handles.axes3)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])

set(handles.edit1,'String','1')

Tampilan GUI untuk proses encoding adalah sebagai berikut:

Tampilan Awal

Load Citra Cover (File penampung/File yang akan disisipi)

Load Citra Message (File yang akan ditampung/File yang akan disisipkan)

Proses Encoding dengan LSB bits = 4

2. Pembuatan GUI Decoding Citra

function varargout = proses_decoding(varargin)
% PROSES_DECODING MATLAB code for proses_decoding.fig
%      PROSES_DECODING, by itself, creates a new PROSES_DECODING or raises the existing
%      singleton*.
%
%      H = PROSES_DECODING returns the handle to a new PROSES_DECODING or the handle to
%      the existing singleton*.
%
%      PROSES_DECODING('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in PROSES_DECODING.M with the given input arguments.
%
%      PROSES_DECODING('Property','Value',...) creates a new PROSES_DECODING or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before proses_decoding_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to proses_decoding_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help proses_decoding

% Last Modified by GUIDE v2.5 02-Jan-2019 08:56:45

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
    'gui_Singleton',  gui_Singleton, ...
    'gui_OpeningFcn', @proses_decoding_OpeningFcn, ...
    'gui_OutputFcn',  @proses_decoding_OutputFcn, ...
    'gui_LayoutFcn',  [] , ...
    'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before proses_decoding is made visible.
function proses_decoding_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to proses_decoding (see VARARGIN)

% Choose default command line output for proses_decoding
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);
movegui(hObject,'center');

% UIWAIT makes proses_decoding wait for user response (see UIRESUME)
% uiwait(handles.figure1);


% --- Outputs from this function are returned to the command line.
function varargout = proses_decoding_OutputFcn(hObject, eventdata, handles)
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;


% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% menampilkan menu open file
[nama_file, nama_path] = uigetfile('*.bmp');
% jika ada file yang dipilih maka akan mengeksekusi perintah di bawahnya
if ~isequal(nama_file,0)
    % membaca file citra
    Img_steg = imread(fullfile(nama_path,nama_file));
    % menampilkan citra pada axes1
    axes(handles.axes1)
    imshow(Img_steg)
    title('Citra Steganografi')
    % menyimpan variabel Img_cover pada lokasi handles
    handles.Img_steg = Img_steg;
    guidata(hObject, handles)
else
    % jika tidak ada file yang dipilih maka akan kembali
    return
end

% --- Executes on button press in pushbutton2.
function pushbutton2_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton2 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% memanggil variabel Img_cover pada lokasi handles
Img_steg = handles.Img_steg;
% membaca LSB bits yang ada di edit1
n = str2double(get(handles.edit1,'String'));
% proses ekstraksi
Img_ext = uint8(bitand(255,bitshift(Img_steg,8-n)));
% menampilkan citra hasil ekstraksi pada axes2
axes(handles.axes2)
imshow(real(Img_ext),[])
title('Hasil Ekstraksi')


function edit1_Callback(hObject, eventdata, handles)
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit1 as text
%        str2double(get(hObject,'String')) returns contents of edit1 as a double


% --- Executes during object creation, after setting all properties.
function edit1_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end


% --- Executes on button press in pushbutton3.
function pushbutton3_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton3 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% mereset button2
axes(handles.axes1)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])

axes(handles.axes2)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])

set(handles.edit1,'String','1')

Tampilan GUI untuk proses decoding adalah sebagai berikut:

Tampilan Awal

Load Citra Steganografi (File yang telah disisipi)

Proses-proses pengolahan citra dalam steganografi antara lain adalah proses decoding dengan LSB bits = 4

Hasil ekstraksi pada proses decoding menunjukkan citra yang sama seperti citra awal yang disisipkan pada proses encoding.

File source code lengkap beserta citra yang ada pada pemrograman di atas dapat diperoleh melalui halaman berikut ini: Source Code