信息隐藏指在设计和确定模块时，使得一个模块内包含的特定信息（过程或数据），对于不需要这些信息的其他模块来说，是透明的。

传统的信息隐藏起源于古老的隐写术。如在古希腊战争中，为了安全地传送军事情报，奴隶主剃光奴隶 的头发，将情报文在奴隶的头皮上，待头发长起后再派出去传送消息。我国古代也早有以藏头诗、藏尾诗、漏格诗以及绘画等形式，将要表达的意思和“密语”隐藏在诗文或画卷中的特定位置，一般人只注意诗或画的表面意境，而不会去注意或破解隐藏其中的密语。 　　信息隐藏的发展历史可以一直追溯到"匿形术（Steganography）"的使用。"匿形术"一词来源于古希腊文中"隐藏的"和"图形"两个词语的组合。虽然"匿形术"与"密码术（Cryptography）"都是致力于信息的保密技术，但是，两者的设计思想却完全不同。"密码术"主要通过设计加密技术，使保密信息不可读，但是对于非授权者来讲，虽然他无法获知保密信息的具体内容，却能意识到保密信息的存在。而"匿形术"则致力于通过设计精妙的方法，使得非授权者根本无从得知保密信息的存在与否。相对于现代密码学来讲，信息隐藏的最大优势在于它并不限制对主信号的存取和访问，而是致力于签字信号的安全保密性。

我们进行信息交换的时候，需要保证数据的安全，所以需要进行适当的信息隐藏。

我们发送一个图片。但是图片里面隐含的加密信息，是就是信息隐藏，只有专属工具能够读出。

所以信息隐藏技术很重要。针对信息安全。

我们来实现一个案例代码。

ＢＭＰ图信息隐藏头文件，请见代码分析

// BMPHider.h: interface for the CBMPHider class.
//
//////////////////////////////////////////////////////////////////////

#if !defined(AFX_BMPHIDER_H__6287D87F_F0AA_4D0C_9502_4674B639CBB5__INCLUDED_)
#define AFX_BMPHIDER_H__6287D87F_F0AA_4D0C_9502_4674B639CBB5__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000
#include <complex>
using namespace std;
class CBMPHider  
{
public:
	CBMPHider();
	virtual ~CBMPHider();
public:
	int m_BitCount;			//位图的图像位数
	WORD * m_pWordData;
	CPalette m_Palette;
	unsigned char *m_pDib, *m_pDibBits;
	unsigned char *m_pOldDibShow;
	DWORD m_dwDibSize;
	BITMAPINFOHEADER *m_pBIH;
	RGBQUAD *m_pPalette;
	int m_nPaletteEntries;
	UINT bitmap_size;
	UINT embfile_size;
	unsigned char *p;		//指向宿主图像数据
	int tag;				//此tag用以标记打开的图像中是否含有隐藏信息0：无 else：有
	unsigned char *q;		//指向隐藏文件数据
	unsigned char *m_pFile;
public:
	BOOL Draw( CDC *pDC, int nX = -1, int nY = -1, int nWidth = -1, int nHeight = -1, int Style = 1);
	BOOL Save( const char *pszFilename );
	BOOL Load( const char * );
	
	void BackUpDib();		//备份图像
	void Pick();			//提取图像
	void Embed();			//嵌入图像
	BOOL LoadEmbFile(const char *);
	BOOL DrawContrast(CDC *pDC,int rect_width, int rect_height);
	void SavePicked( const char *pszFilename );	

};

#endif // !defined(AFX_BMPHIDER_H__6287D87F_F0AA_4D0C_9502_4674B639CBB5__INCLUDED_)

请见详细代码实现

#include "stdafx.h"
#include "BMPHider.h"

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

CBMPHider::CBMPHider()
{
	m_pDib = NULL;
	m_pWordData = NULL;
	m_pFile = NULL;
	m_pOldDibShow = NULL;
}

CBMPHider::~CBMPHider()
{
	if( m_pDib != NULL )
		delete [] m_pDib;
	if( m_pWordData != NULL )
		delete [] m_pWordData;
	if (m_pFile != NULL)
		delete [] m_pFile;
	if (m_pOldDibShow != NULL)
		delete [] m_pOldDibShow;
}

BOOL CBMPHider::Load( const char *pszFilename )
{
	CFile cf;
	if( !cf.Open( pszFilename, CFile::modeRead ) )
		return( FALSE );
	
	DWORD dwDibSize;
	dwDibSize =
		cf.GetLength() - sizeof( BITMAPFILEHEADER );

	unsigned char *pDib;
	pDib = new unsigned char [dwDibSize];
	if( pDib == NULL )
		return( FALSE );

	BITMAPFILEHEADER BFH;
	try
	{
		if( cf.Read( &BFH, sizeof( BITMAPFILEHEADER ) )
			!= sizeof( BITMAPFILEHEADER ) ||
			BFH.bfType != 'MB' ||
			cf.Read( pDib, dwDibSize ) != dwDibSize )
		{
			delete [] pDib;
			return( FALSE );
		}
	}
	
	catch( CFileException *e )
	{
		e->Delete();
		delete [] pDib;
		return( FALSE );
	}
	cf.Close();
	if( m_pDib != NULL )
		delete m_pDib;
	if (BFH.bfReserved1 != 0)          //含有隐藏信息，保存其大小
	{
		if (BFH.bfReserved2 == 0)
			embfile_size = BFH.bfReserved1;
		else
			embfile_size = BFH.bfReserved1 + 65535;
	}
	m_pDib = pDib;
	m_dwDibSize = dwDibSize;
	m_pBIH = (BITMAPINFOHEADER *) m_pDib;
	m_pPalette =(RGBQUAD *) &m_pDib[sizeof(BITMAPINFOHEADER)];
	m_nPaletteEntries = 1 << m_pBIH->biBitCount;
	if( m_pBIH->biBitCount > 8 )         
		m_nPaletteEntries = 0;
	else if( m_pBIH->biClrUsed != 0 )
		m_nPaletteEntries = m_pBIH->biClrUsed;
	m_pDibBits = &m_pDib[sizeof(BITMAPINFOHEADER)+
			m_nPaletteEntries*sizeof(RGBQUAD)];

	if( m_Palette.GetSafeHandle() != NULL )
		m_Palette.DeleteObject();

	if( m_nPaletteEntries != 0 )
	{      

		LOGPALETTE *pLogPal = (LOGPALETTE *) new char
				[sizeof(LOGPALETTE)+
				m_nPaletteEntries*sizeof(PALETTEENTRY)];

		if( pLogPal != NULL )
		{
			pLogPal->palVersion = 0x300;
			pLogPal->palNumEntries = m_nPaletteEntries;

			for( int i=0; i<m_nPaletteEntries; i++ )
			{
				pLogPal->palPalEntry[i].peRed =
					m_pPalette[i].rgbRed;
				pLogPal->palPalEntry[i].peGreen =
					m_pPalette[i].rgbGreen;
				pLogPal->palPalEntry[i].peBlue =
					m_pPalette[i].rgbBlue;
			}

			m_Palette.CreatePalette( pLogPal );
			delete [] pLogPal;
		}
	}

	m_BitCount = 24;             //24位位图
	p = m_pDibBits;              //指向位图数据的指针，用来执行处理操作用
	bitmap_size = m_dwDibSize - (m_pDibBits - m_pDib);//真正的位图数据的大小（即除头结构外）
	
	tag = BFH.bfReserved1;
	return( TRUE );

}

BOOL CBMPHider::Save( const char *pszFilename ) //保存含有隐藏信息的bmp
{
	if( m_pDib == NULL )
		return( FALSE );
	CFile cf;
	if( !cf.Open( pszFilename,
		CFile::modeCreate | CFile::modeWrite ) )
		return( FALSE );
	try
	{
		BITMAPFILEHEADER BFH;
		memset( &BFH, 0, sizeof( BITMAPFILEHEADER ) );
		BFH.bfType = 'MB';
		BFH.bfSize = sizeof( BITMAPFILEHEADER ) + m_dwDibSize;
		BFH.bfOffBits = sizeof( BITMAPFILEHEADER ) +
			sizeof( BITMAPINFOHEADER ) +
			m_nPaletteEntries * sizeof( RGBQUAD );
		if (embfile_size <= 65535)   
			//由于bfReserved1是unsigned short型的，大小可能不能满足要求,可能要用到reserved2
			BFH.bfReserved1 = embfile_size;   
		else
		{
			BFH.bfReserved1 = embfile_size - 65535;
			BFH.bfReserved2 = 1; //标记
		}
		cf.Write( &BFH, sizeof( BITMAPFILEHEADER ) );
		cf.Write( m_pDib, m_dwDibSize );
	}
	catch( CFileException *e )
	{
		e->Delete();
		return( FALSE );
	}
	return( TRUE );
}

BOOL CBMPHider::Draw( CDC *pDC, int nX, int nY, int nWidth, int nHeight, int Style )
{
 	if( m_pDib == NULL )
		return( FALSE );
 	long vWidth = m_pBIH->biWidth;
 	if( nWidth == -1 )
 		nWidth = m_pBIH->biWidth;
	if( nHeight == -1 )
 		nHeight = m_pBIH->biHeight;
 	if (Style)   
 	{
 		StretchDIBits( pDC->m_hDC, nX, nY,
 			nWidth, nHeight,
 			0, 0,
 			m_pBIH->biWidth, m_pBIH->biHeight,
 			m_pDibBits,
 			(BITMAPINFO *) m_pBIH,
			BI_RGB, SRCCOPY );
 	}
 	else
 	{
		SetDIBitsToDevice( pDC->m_hDC, nX, nY,
 			m_pBIH->biWidth, m_pBIH->biHeight,
			0, 0,
 			0, m_pBIH->biHeight,
 			m_pDibBits,
 			(BITMAPINFO *) m_pBIH,
 			BI_RGB);
 	}
	return( TRUE );
}



BOOL CBMPHider::LoadEmbFile(const char * pszFilename)
{	
	CFile cf;
	if( !cf.Open( pszFilename, CFile::modeRead ) )
		return( FALSE );

	DWORD dwFileSize;
	dwFileSize = cf.GetLength();

	embfile_size = dwFileSize;
	unsigned char *pFile;
	pFile = new unsigned char [dwFileSize];
	cf.Read( pFile, dwFileSize );       //将文件中内容读入数组，解下来就开始嵌入操作

	m_pFile = pFile;
	q = pFile;        //记录下位置
	return true;
}

void CBMPHider::Embed()//嵌入
{
	unsigned char bmdata;//bitmap data
	unsigned char efdata;//embeddedfile data
	int t = 7;		
	int x[8];	
	int s[8];
	int last_bit; //记录字节最低位本来的bit

	for(UINT i1 = 0, i2 = 0; i1 <= bitmap_size - 1, i2 <= embfile_size - 1; i1++)
	{
		bmdata = *p;

		for (int j = 0; j <= 7; j++) //计算各bit位
		{
			x[j] = bmdata & 1;
			bmdata >>= 1;
		}
		
		last_bit = x[0];
		x[0] = x[1] ^ x[2] ^ x[3] ^ x[4] ^ x[5] ^ x[6] ^ x[7];
		
		if (t == 7)    //宿主图片每走过八个字节，计算一次s[]
		{
			efdata = *q;
			for (j = 0; j <= 7; j++)
			{
				s[j] = efdata & 1;
				efdata >>= 1;
			}
		}
		x[0] ^= s[t];//隐藏信息
		if (last_bit == 0)  //嵌入隐藏信息
		{
			*p |= x[0];
		}
		else
		{
			*p &= 254 + x[0];
		}
	
		p++;
		t--;
		if (t == -1)  //需要计算一次s[]
		{
			t = 7;
			q++;
			i2++;
		}
	}

}

void CBMPHider::Pick()//提取
{
	m_pFile = new unsigned char [embfile_size];
	unsigned char *q = m_pFile;

	unsigned char bmdata;//bitmap data

	int x[8];	
	int s[8];
	int t = 7;
	for (UINT i1 = 0, i2 = 0; i1 <= bitmap_size - 1, i2 <= embfile_size - 1; i1++)
	{
		bmdata = *p;
		for (int j = 0; j <= 7; j++) //计算各bit位
		{
			x[j] = bmdata & 1;
			bmdata >>= 1;
		}
		s[t] = x[0] ^ x[1] ^ x[2] ^ x[3] ^ x[4] ^ x[5] ^ x[6] ^ x[7];
		t--;
		if (t == -1) //s[7]到s[0]组成一个字节
		{
			*q = s[7] * 128 + s[6] * 64 + s[5] * 32 + s[4] * 16 + 
				s[3] * 8 + s[2] * 4 + s[1] * 2 + s[0];
			t = 7;
			i2++;
			q++;
		}
		p++;
	}

}
	
void CBMPHider::SavePicked( const char *pszFilename )
{
	CFile cf;
	cf.Open( pszFilename, CFile::modeCreate | CFile::modeWrite );
	cf.Write( m_pFile, embfile_size );
}

void CBMPHider::BackUpDib()
{
	m_pOldDibShow = new unsigned char [bitmap_size];
   
	::CopyMemory(m_pOldDibShow, m_pDibBits, bitmap_size); //将原始的数据单独保存以便对比显示
}

BOOL CBMPHider::DrawContrast(CDC *pDC, int rect_width, int rect_height)
{                             //看原图，如果容纳得下两个图，则不要压缩，否则要压缩
	if (m_pOldDibShow == NULL)
		return FALSE;
	if (rect_width >= 2*m_pBIH->biWidth + 30 && rect_height >= m_pBIH->biHeight)
	{
		StretchDIBits( pDC->m_hDC, 0, 0,
		m_pBIH->biWidth, m_pBIH->biHeight,
		0, 0,
		m_pBIH->biWidth, m_pBIH->biHeight,
		m_pOldDibShow,
		(BITMAPINFO *) m_pBIH,
		BI_RGB, SRCCOPY );    // 原图

		StretchDIBits( pDC->m_hDC, m_pBIH->biWidth+30, 0,
		m_pBIH->biWidth, m_pBIH->biHeight,
		0, 0,
		m_pBIH->biWidth, m_pBIH->biHeight,
		m_pDibBits,
		(BITMAPINFO *) m_pBIH,
		BI_RGB, SRCCOPY );    // 嵌入隐藏信息的图
	}
	else
	{
		int scale_i = m_pBIH->biWidth * 5 / (rect_width*2);
		int scale_j = m_pBIH->biHeight / rect_height;
		if (scale_i < scale_j)
			scale_i = scale_j;

		StretchDIBits( pDC->m_hDC, 0, 0,
		m_pBIH->biWidth / scale_i, m_pBIH->biHeight / scale_i,
		0, 0,
		m_pBIH->biWidth, m_pBIH->biHeight,
		m_pOldDibShow,
		(BITMAPINFO *) m_pBIH,
		BI_RGB, SRCCOPY );    // 原图

		StretchDIBits( pDC->m_hDC, m_pBIH->biWidth / scale_i+30, 0,
		m_pBIH->biWidth / scale_i, m_pBIH->biHeight / scale_i,
		0, 0,
		m_pBIH->biWidth, m_pBIH->biHeight,
		m_pDibBits,
		(BITMAPINFO *) m_pBIH,
		BI_RGB, SRCCOPY );    // 嵌入隐藏信息的图

	}

	return TRUE;
}

具体代码调用实现

#include "stdafx.h"
#include "DataHideInBMP.h"

#include "DataHideInBMPDoc.h"
#include "DataHideInBMPView.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CDataHideInBMPView

IMPLEMENT_DYNCREATE(CDataHideInBMPView, CView)

BEGIN_MESSAGE_MAP(CDataHideInBMPView, CView)
	//{{AFX_MSG_MAP(CDataHideInBMPView)
	ON_COMMAND(ID_NORMAL, OnNormal)
	ON_COMMAND(ID_STRETCH, OnStretch)
	ON_COMMAND(ID_FILE_OPEN, OnFileOpen)
	ON_COMMAND(ID_EMBED, OnEmbed)
	ON_UPDATE_COMMAND_UI(ID_EMBED, OnUpdateEmbed)
	ON_COMMAND(ID_PICK, OnPick)
	ON_UPDATE_COMMAND_UI(ID_PICK, OnUpdatePick)
	//}}AFX_MSG_MAP
	// Standard printing commands
	ON_COMMAND(ID_FILE_PRINT, CView::OnFilePrint)
	ON_COMMAND(ID_FILE_PRINT_DIRECT, CView::OnFilePrint)
	ON_COMMAND(ID_FILE_PRINT_PREVIEW, CView::OnFilePrintPreview)
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CDataHideInBMPView construction/destruction

CDataHideInBMPView::CDataHideInBMPView()
{
	// TODO: add construction code here
	ImageStyle = 0;
    have_open_a_file = false;

	embed = false;
	pick = false;
	show_contrast = false;
}

CDataHideInBMPView::~CDataHideInBMPView()
{
}

BOOL CDataHideInBMPView::PreCreateWindow(CREATESTRUCT& cs)
{
	// TODO: Modify the Window class or styles here by modifying
	//  the CREATESTRUCT cs
	WNDCLASSEX wndcls;
	wndcls.cbSize=sizeof(WNDCLASSEX);
	HINSTANCE hinst=AfxGetInstanceHandle();
	if(CView::PreCreateWindow(cs)&&cs.lpszClass!=NULL)
	{
		HBRUSH hbkbrush=CreateSolidBrush(RGB(0,0,0));
		if(!GetClassInfoEx(hinst,cs.lpszClass,&wndcls))
			return FALSE;
		UnregisterClass(cs.lpszClass,hinst);
		wndcls.hbrBackground=hbkbrush;
		RegisterClassEx(&wndcls);  
		return TRUE;
	}
	else
		return FALSE;
	return CView::PreCreateWindow(cs);
}

/////////////////////////////////////////////////////////////////////////////
// CDataHideInBMPView drawing

void CDataHideInBMPView::OnDraw(CDC* pDC)
{
	CDataHideInBMPDoc* pDoc = GetDocument();
	ASSERT_VALID(pDoc);
	// TODO: add draw code for native data here
	RECT Rect;
	GetClientRect( &Rect );

	if (!show_contrast)
		m_BMPHider.Draw( pDC, 0, 0, Rect.right, Rect.bottom, ImageStyle );
	else
	{
		m_BMPHider.DrawContrast(pDC, Rect.right, Rect.bottom);
		pDC->SetBkColor((0,0,0));
		pDC->SetTextColor((255,255,255));
		pDC->TextOut(0, Rect.bottom-30, "左图为原始图，右图为嵌入了隐藏信息的图");
	}
}

/////////////////////////////////////////////////////////////////////////////
// CDataHideInBMPView printing

BOOL CDataHideInBMPView::OnPreparePrinting(CPrintInfo* pInfo)
{
	// default preparation
	return DoPreparePrinting(pInfo);
}

void CDataHideInBMPView::OnBeginPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{
	// TODO: add extra initialization before printing
}

void CDataHideInBMPView::OnEndPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{
	// TODO: add cleanup after printing
}

/////////////////////////////////////////////////////////////////////////////
// CDataHideInBMPView diagnostics

#ifdef _DEBUG
void CDataHideInBMPView::AssertValid() const
{
	CView::AssertValid();
}

void CDataHideInBMPView::Dump(CDumpContext& dc) const
{
	CView::Dump(dc);
}

CDataHideInBMPDoc* CDataHideInBMPView::GetDocument() // non-debug version is inline
{
	ASSERT(m_pDocument->IsKindOf(RUNTIME_CLASS(CDataHideInBMPDoc)));
	return (CDataHideInBMPDoc*)m_pDocument;
}
#endif //_DEBUG

/////////////////////////////////////////////////////////////////////////////
// CDataHideInBMPView message handlers

void CDataHideInBMPView::OnNormal() 
{
	// TODO: Add your command handler code here
	ImageStyle = 0;

	CMenu *pMnu = AfxGetMainWnd()->GetMenu( );
	pMnu->CheckMenuItem(ID_STRETCH,MF_UNCHECKED);
	pMnu->CheckMenuItem(ID_NORMAL,MF_CHECKED);
	
	InvalidateRect( NULL, TRUE );
	UpdateWindow();	
}

void CDataHideInBMPView::OnStretch() 
{
	// TODO: Add your command handler code here
	ImageStyle = 1;
	
	CMenu *pMnu = AfxGetMainWnd()->GetMenu( );
	pMnu->CheckMenuItem(ID_STRETCH,MF_CHECKED);
	pMnu->CheckMenuItem(ID_NORMAL,MF_UNCHECKED);
	
	InvalidateRect( NULL, TRUE );
	UpdateWindow();	
}

void CDataHideInBMPView::OnFileOpen() 
{
	// TODO: Add your command handler code here
	show_contrast = false;   //非对比显示
	static char szFilter[] = "BMP Files(*.BMP)|*.BMP||";

	CFileDialog FileDlg( TRUE, NULL, NULL,
		OFN_HIDEREADONLY, szFilter );

	if( FileDlg.DoModal() == IDOK &&
		m_BMPHider.Load( FileDlg.GetPathName() ) )
	{
		InvalidateRect( NULL, TRUE );
		UpdateWindow();
		have_open_a_file=true;
		if (m_BMPHider.tag == 0)//该图无隐藏信息
		{
			embed = true;
			pick = false;  //菜单亮暗控制
		}//
		else
		{
			embed = false;
			pick = true;  //菜单亮暗控制
		}//
	}	
}

void CDataHideInBMPView::OnEmbed() 
{
	// TODO: Add your command handler code here
	//弹出打开对话框，用户选择嵌入的文件

	static char szFilter[] = "All Files(*.*)|*.*||";

	CFileDialog FileDlg( TRUE, NULL, NULL,
		OFN_HIDEREADONLY, szFilter );

	if( FileDlg.DoModal() == IDOK &&
		m_BMPHider.LoadEmbFile( FileDlg.GetPathName() ) )
	{ 
		if (m_BMPHider.bitmap_size / m_BMPHider.embfile_size < 8)
		{
			AfxMessageBox("文件太大，无法嵌入！");
		}
		else
		{
			show_contrast = true;
			m_BMPHider.BackUpDib(); //图片原始数据备份供对比显示
			m_BMPHider.Embed();   //嵌入
			
			Invalidate(true);//刷屏，显示加入隐藏信息后的图像
			
			static char szFilter[] = "BMP Files(*.BMP)|*.BMP||";
			CFileDialog FileDlg( FALSE, "bmp", NULL,                //保存
				OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT, szFilter );
			
			if( FileDlg.DoModal() == IDOK )
			{
				m_BMPHider.Save( FileDlg.GetPathName() );
			}
			embed = false;
		}
		
	}	
}

void CDataHideInBMPView::OnUpdateEmbed(CCmdUI* pCmdUI) 
{
	// TODO: Add your command update UI handler code here
	pCmdUI->Enable(embed);	
}

void CDataHideInBMPView::OnPick() 
{
	// TODO: Add your command handler code here
	//提取完毕，弹出保存对话框，用户进行保存
	static char szFilter[] = "All Files(*.*)|*.*||";
	CFileDialog FileDlg( FALSE, "", NULL,                //保存
		OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT, szFilter );
				
	if (FileDlg.DoModal() == IDOK)
	{	
		m_BMPHider.Pick();
		m_BMPHider.SavePicked(FileDlg.GetPathName());
		pick = false;
	}	
}

void CDataHideInBMPView::OnUpdatePick(CCmdUI* pCmdUI) 
{
	// TODO: Add your command update UI handler code here
	pCmdUI->Enable(pick);	
}