Microsoft supports two versions of the CryptoAPI: the base provider, rsabase.dll, and the enhanced provider, rsaenh.dll. The standard version of NT installs rsabase.dll, and the high-encryption version installs rsaenh.dll. Table 1 shows the differences between the key lengths of the base-provider and enhanced-provider DLLs. The enhanced-provider DLL doubles the key lengths for public-key and secret-key algorithms and adds DES or 3DES encryption. The base-provider RC2 and RC4 key lengths are 56 bits in SP6a and later and 40 bits in earlier versions.
别人写的一个例子，参考吧static BOOL EncryptFile( PCHAR szSource, PCHAR szDestination, PCHAR szPassword) //-------------------------------------------------------------------- // Parameters passed are: // szSource, the name of the input, a plaintext file. // szDestination, the name of the output, an encrypted file to be // created. // szPassword, the password. { //-------------------------------------------------------------------- // Declare and initialize local variables.
//-------------------------------------------------------------------- // Determine the block size. If a block cipher is used, // it must have room for an extra block.
//-------------------------------------------------------------------- // Allocate memory. if(pbBuffer = (BYTE *)malloc(dwBufferLen)) { printf("Memory has been allocated for the buffer. \n"); } else { HandleError("Out of memory. \n"); } //-------------------------------------------------------------------- // In a do loop, encrypt the source file and write to the source file.
do {
//-------------------------------------------------------------------- // Read up to dwBlockLen bytes from the source file. dwCount = fread(pbBuffer, 1, dwBlockLen, hSource); if(ferror(hSource)) { HandleError("Error reading plaintext!\n"); }
} while(!feof(hSource)); //-------------------------------------------------------------------- // End the do loop when the last block of the source file has been // read, encrypted, and written to the destination file.
//-------------------------------------------------------------------- // Close files.
PCHAR szSource,
PCHAR szDestination,
PCHAR szPassword)
//--------------------------------------------------------------------
// Parameters passed are:
// szSource, the name of the input, a plaintext file.
// szDestination, the name of the output, an encrypted file to be
// created.
// szPassword, the password.
{
//--------------------------------------------------------------------
// Declare and initialize local variables.
FILE *hSource;
FILE *hDestination;
HCRYPTPROV hCryptProv;
HCRYPTKEY hKey;
HCRYPTHASH hHash;
PBYTE pbBuffer;
DWORD dwBlockLen;
DWORD dwBufferLen;
DWORD dwCount;
//--------------------------------------------------------------------
// Open source file.
if(hSource = fopen(szSource,"rb"))
{
printf("The source plaintext file, %s, is open. \n", szSource);
}
else
{
HandleError("Error opening source plaintext file!");
} //--------------------------------------------------------------------
// Open destination file.
if(hDestination = fopen(szDestination,"wb"))
{
printf("Destination file %s is open. \n", szDestination);
}
else
{
HandleError("Error opening destination ciphertext file!");
} //以下获得一个CSP句柄
if(CryptAcquireContext(
&hCryptProv,
NULL, //NULL表示使用默认密钥容器，默认密钥容器名为用户登陆名
NULL,
PROV_RSA_FULL,
0))
{
printf("A cryptographic provider has been acquired. \n");
}
else//密钥容器不存在
{
if(CryptAcquireContext(
&hCryptProv,
NULL,
NULL,
PROV_RSA_FULL,
CRYPT_NEWKEYSET))//创建密钥容器
{
//创建密钥容器成功，并得到CSP句柄
printf("A new key container has been created.\n");
}
else
{
HandleError("Could not create a new key container.\n");
}
} //--------------------------------------------------------------------
// 创建一个会话密钥（session key）
// 会话密钥也叫对称密钥，用于对称加密算法。
// （注: 一个Session是指从调用函数CryptAcquireContext到调用函数
// CryptReleaseContext 期间的阶段。） //--------------------------------------------------------------------
// Create a hash object.
if(CryptCreateHash(
hCryptProv,
CALG_MD5,
0,
0,
&hHash))
{
printf("A hash object has been created. \n");
}
else
{
HandleError("Error during CryptCreateHash!\n");
} //--------------------------------------------------------------------
// 用输入的密码产生一个散列
if(CryptHashData(
hHash,
(BYTE *)szPassword,
strlen(szPassword),
0))
{
printf("The password has been added to the hash. \n");
}
else
{
HandleError("Error during CryptHashData. \n");
} //--------------------------------------------------------------------
// 通过散列生成会话密钥(session key)
if(CryptDeriveKey(
hCryptProv,
ENCRYPT_ALGORITHM,
hHash,
KEYLENGTH,
&hKey))
{
printf("An encryption key is derived from the password hash. \n");
}
else
{
HandleError("Error during CryptDeriveKey!\n");
}
//--------------------------------------------------------------------
// Destroy the hash object.
CryptDestroyHash(hHash);
hHash = NULL;
//--------------------------------------------------------------------
// The session key is now ready.
//--------------------------------------------------------------------
// 因为加密算法是按ENCRYPT_BLOCK_SIZE 大小的块加密的，所以被加密的
// 数据长度必须是ENCRYPT_BLOCK_SIZE 的整数倍。下面计算一次加密的
// 数据长度。 dwBlockLen = 1000 - 1000 % ENCRYPT_BLOCK_SIZE;
//--------------------------------------------------------------------
// Determine the block size. If a block cipher is used,
// it must have room for an extra block.
if(ENCRYPT_BLOCK_SIZE > 1)
dwBufferLen = dwBlockLen + ENCRYPT_BLOCK_SIZE;
else
dwBufferLen = dwBlockLen;
//--------------------------------------------------------------------
// Allocate memory.
if(pbBuffer = (BYTE *)malloc(dwBufferLen))
{
printf("Memory has been allocated for the buffer. \n");
}
else
{
HandleError("Out of memory. \n");
}
//--------------------------------------------------------------------
// In a do loop, encrypt the source file and write to the source file.
do
{
//--------------------------------------------------------------------
// Read up to dwBlockLen bytes from the source file.
dwCount = fread(pbBuffer, 1, dwBlockLen, hSource);
if(ferror(hSource))
{
HandleError("Error reading plaintext!\n");
}
//--------------------------------------------------------------------
// 加密数据
if(!CryptEncrypt(
hKey, //密钥
0, //如果数据同时进行散列和加密，这里传入一个散列对象
feof(hSource), //如果是最后一个被加密的块，输入TRUE.如果不是输入FALSE.
//这里通过判断是否到文件尾来决定是否为最后一块。
0, //保留
pbBuffer, //输入被加密数据，输出加密后的数据
&dwCount, //输入被加密数据实际长度，输出加密后数据长度
dwBufferLen)) //pbBuffer的大小。
{
HandleError("Error during CryptEncrypt. \n");
}
//--------------------------------------------------------------------
// Write data to the destination file.
fwrite(pbBuffer, 1, dwCount, hDestination);
if(ferror(hDestination))
{
HandleError("Error writing ciphertext.");
}
}
while(!feof(hSource));
//--------------------------------------------------------------------
// End the do loop when the last block of the source file has been
// read, encrypted, and written to the destination file.
//--------------------------------------------------------------------
// Close files.
if(hSource)
fclose(hSource);
if(hDestination)
fclose(hDestination);
//--------------------------------------------------------------------
// Free memory.
if(pbBuffer)
free(pbBuffer);
//--------------------------------------------------------------------
// Destroy session key.
if(hKey)
CryptDestroyKey(hKey);
//--------------------------------------------------------------------
// Destroy hash object.
if(hHash)
CryptDestroyHash(hHash);
//--------------------------------------------------------------------
// Release provider handle.
if(hCryptProv)
CryptReleaseContext(hCryptProv, 0);
return(TRUE);
} // End of Encryptfile