使用 Visual C++创建Crypto加/解密组件

 
使用 Visual C++创建Crypto加/解密组件
简介
这篇文章将教你如何使用 Visual C++ 和 ATL 工具和 Microsoft CryptoAPI 建立一个能加/解密数据的组件。
Crypto 101
本文使用Microsoft® Cryptographic Application Programming Interface (CryptoAPI),将苦涩难懂的逻辑算法操作隐藏起来，如果想知道详细信息请参看MSDN Library.如果想知道更多的密码系统，我推荐你看看这本书 Bruce Schneier's Applied Cryptography: Protocols, Algorithms, and Source Code in C

建立组件
首先，用"ATL COM AppWizard”建立一个新project。在这个例子中，我将其命名为”CryptoProj”。在 server type中选择”Dynamic Link Library (DLL)”，点按”Finish”继续。

定义界面
在 insert 菜单中点按"New ATL Object..."，选择 “Simple Object”，然后按 Next。

在 “Names” 栏中，设 short name 为 “Crypto”，其他项照下面的填写。

在 Attributes  栏，确定 Apartment Threading Model 被选上，Support IsupportErrorInfo 选项勾上，然后按 OK.

按右键点击 Icrypto ，点”Add Method”加一个方法.

将该方法取名为”Encrypt”，在参数栏输入"[in] BSTR bstrPlainText, [in] BSTR bstrPassword, [out, retval] VARIANT *vCipherText".

再加一个方法，取名为”Decrypt”，参数为"[in] VARIANT vCipherText, [in] BSTR bstrPassword, [out, retval] BSTR *bstrPlainText"

实现加密方法
需要包括 CryptoAPI 库，在 Crypto.cpp 头加一句：

#include <wincrypt.h>

现在来定义我们需要的各种变量。

STDMETHODIMP CCrypto::Encrypt(BSTR bstrPlainText,

                              BSTR bstrPassword,

                              VARIANT *vCipherText)

{

        BYTE *pbData;

        BYTE *pbPassword;

        SAFEARRAY* psa;

        HCRYPTPROV hProv   = 0;

        HCRYPTHASH hHash   = 0;

        HCRYPTKEY hKey     = 0;

        DWORD dwCryptDataLen = 0;

        DWORD dwDataLen = 0;

        DWORD dwError = 0;

        char  buffer[200];

        USES_CONVERSION;

由于许多CryptoAPI 调用要用注册表，所以需要执行一句RevertToSelf().

RevertToSelf();

下一步，我们需要将输入变量转化为我们能用的格式。

dwDataLen = SysStringLen(bstrPlainText);

pbData = (BYTE*)OLE2A(bstrPlainText);

pbPassword = (BYTE*)OLE2A(bstrPassword);

然后，用CryptAcquireContext function取得省缺 Crypto provider的句柄。

// Get handle to the default provider.

if (! CryptAcquireContext(&hProv,

   "aspZoneCryptoComponent/0", MS_DEF_PROV, 

   PROV_RSA_FULL, CRYPT_MACHINE_KEYSET))

{

        if (! CryptAcquireContext(&hProv,

           "aspZoneCryptoComponent/0", MS_DEF_PROV,

           PROV_RSA_FULL, (CRYPT_NEWKEYSET |

           CRYPT_MACHINE_KEYSET)))

        {

               dwError = GetLastError();

               sprintf(buffer, "Error %x during CryptAcquireContext",

                  dwError);

               return Error(buffer);

        }

}

我们通过创建一个 one-way-hash密码得到session key。

// Create a hash object.

if ( ! CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {

        dwError = GetLastError();

        sprintf(buffer, "Error %x during CryptCreateHash", dwError);

        return Error(buffer);

}

// Hash in the password.

if ( ! CryptHashData(hHash, pbPassword, SysStringLen(bstrPassword), 0)) {

        dwError = GetLastError();

        sprintf(buffer, "Error %x during CryptHashData", dwError);

        return Error(buffer);

}

// Derive a session key from the hash object.

if ( ! CryptDeriveKey(hProv, ENCRYPT_ALGORITHM, hHash, 0, &hKey)) {

        dwError = GetLastError();

        sprintf(buffer, "Error %x during CryptDeriveKey", dwError);

        return Error(buffer);

}

// Destroy hash object.

CryptDestroyHash(hHash);

hHash = 0;

现在来加密我们的数据。

// Encrypt the Data.

dwCryptDataLen = dwDataLen;

if ( ! CryptEncrypt(hKey, 0, true, 0, pbData, &dwCryptDataLen, dwDataLen)) {

        dwError = GetLastError();

        sprintf(buffer, "Error %x during CryptEncrypt", dwError);

        return Error(buffer);

}

我们将加密后的数据放入一个数组中，而不是一个string里，因为它可能会包含null。虽然 BSTR 能处理null的情况，但不能保证用户调用环境能正确处理，所以一个数组是最好的选择。

// Place Encrypted Data into a VARIANT SAFEARRAY of VARIANT BYTE

SAFEARRAYBOUND rgsabound[] = {dwCryptDataLen, 0};

psa = SafeArrayCreate(VT_VARIANT, 1, rgsabound);

VARIANT* rgElems;

SafeArrayAccessData(psa, (LPVOID*)&rgElems);

for(DWORD i=0;i<dwCryptDataLen;i++){

        VariantInit(&rgElems[i]);

        rgElems[i].vt = VT_UI1;

        rgElems[i].uiVal = pbData[i];

}

SafeArrayUnaccessData(psa);

VariantInit(vCipherText);

vCipherText->vt = (VT_ARRAY | VT_VARIANT) ;

vCipherText->parray = psa;

稍微整理一下，搞定。

// Destroy session key.

if(hKey) CryptDestroyKey(hKey);

 // Release provider handle.

if(hProv) CryptReleaseContext(hProv, 0);

return S_OK;

实现解密方法
首先定义变量。

STDMETHODIMP CCrypto::Decrypt(VARIANT vCipherText,

                              BSTR bstrPassword,

                              BSTR *bstrPlainText)

{

        HCRYPTPROV hProv   = 0;

        HCRYPTHASH hHash   = 0;

        HCRYPTKEY hKey     = 0;

        SAFEARRAY* psa;

        VARIANT HUGEP *pVar;

        BYTE *pbData;

        BYTE *pbPassword;

        long lBound, uBound;

        DWORD dwCryptDataLen = 0;

        DWORD dwOffset = 0;

        DWORD dwError = 0;

        char  buffer[200];

        USES_CONVERSION;

同样的原因，我们要调用RevertToSelf()

RevertToSelf();

现在，当接收一个数组参数作为变量，该数组可能藏在结构中的某个地方，所以需要一个判断嵌套。

//Get the safe array out of the Variant.

if (vCipherText.vt == (VT_VARIANT | VT_BYREF))

{

     if (vCipherText.pvarVal->vt == (VT_ARRAY | VT_VARIANT))           

          SafeArrayCopy(vCipherText.pvarVal->parray, &psa);

     else

     {

     if (vCipherText.pvarVal->vt == (VT_ARRAY | VT_VARIANT | VT_BYREF))

          SafeArrayCopy(*(vCipherText.pvarVal->pparray), &psa);

     }

}

else

{

     if (vCipherText.vt == (VT_ARRAY | VT_VARIANT | VT_BYREF))

          SafeArrayCopy(*(vCipherText.pparray), &psa);

     else

     {

          if (vCipherText.vt == (VT_ARRAY | VT_VARIANT))

               SafeArrayCopy(vCipherText.parray, &psa);

          else

               return DISP_E_TYPEMISMATCH;

     }

}

需要密文和密码都是BYTE*类型。

//Convert the SAFEARRAY into a form we can use.

SafeArrayAccessData(psa, (void HUGEP* FAR*)&pVar);

SafeArrayGetLBound(psa, 1, &lBound);

SafeArrayGetUBound(psa, 1, &uBound);

dwOffset = 0 - lBound;

dwCryptDataLen = uBound + dwOffset + 1;

//Allocate memory

pbData = (BYTE *)malloc(dwCryptDataLen);

//Copy the array

for(DWORD i = lBound; i <= uBound; i++){ if( ! (pVar[i].vt & VT_UI1)){ //Data Elements must be VT_UI1 (Bytes). free(pbData); return DISP_E_TYPEMISMATCH; } pbData[i + dwOffset]="pVar[i].uiVal;" } //Get Password pbPassword="(BYTE*)OLE2A(bstrPassword);</PRE">

取得 Crypto Provider  的句柄。

// Get handle to the default provider.

if (! CryptAcquireContext(&hProv, "aspZoneCryptoComponent/0",

     MS_DEF_PROV, PROV_RSA_FULL, CRYPT_MACHINE_KEYSET))

{

     if (! CryptAcquireContext(&hProv, "aspZoneCryptoComponent/0",

          MS_DEF_PROV, PROV_RSA_FULL, (CRYPT_NEWKEYSET | CRYPT_MACHINE_KEYSET)))

     {

          dwError = GetLastError();

          sprintf(buffer, "Error %x during CryptAcquireContext", dwError);

          return Error(buffer);

     }

}

从 password 中得到 session key.

// Create a hash object.

if ( ! CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {

     dwError = GetLastError();

     sprintf(buffer, "Error %x during CryptCreateHash", dwError);

     return Error(buffer);

}

// Hash in the password.

if ( ! CryptHashData(hHash, pbPassword, SysStringLen(bstrPassword), 0)) {

     dwError = GetLastError();

     sprintf(buffer, "Error %x during CryptHashData", dwError);

     return Error(buffer);

}

// Derive a session key from the hash object.

if ( ! CryptDeriveKey(hProv, ENCRYPT_ALGORITHM, hHash, 0, &hKey)) {

     dwError = GetLastError();

     sprintf(buffer, "Error %x during CryptDeriveKey", dwError);

     return Error(buffer);

}

// Destroy hash object.

CryptDestroyHash(hHash);

hHash = 0;

将密文解密到纯文本中。

// Decrypt the Data.

if ( ! CryptDecrypt(hKey, 0, true, 0, pbData, &dwCryptDataLen)) {

     dwError = GetLastError();

     sprintf(buffer, "Error %x during CryptDecrypt", dwError);

     return Error(buffer);

}

//Terminate the string with a null

pbData[dwCryptDataLen] = NULL;

设置返回值，大扫除，然后搞定。

//Place Decrypted data into retval

*bstrPlainText = SysAllocString(A2OLE((const char *)pbData));

// Destroy session key.

if(hKey) CryptDestroyKey(hKey);

 // Release provider handle.

if(hProv) CryptReleaseContext(hProv, 0);

return S_OK;

}

翻译：讨饭猫
Jan,10 2000
下载doc文档（带图）：
http://64.13.189.254/cafecat/build a crypto component using Visual C++ and ATL .doc