用 CryptoAPI加密的一个例子

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一个文件加密的例子
言归正传，我们来看一段文件加密的代码。
`#include <stdio.h>

include <windows.h>

include <wincrypt.h>

define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)

define KEYLENGTH 0x00800000

void HandleError(char *s);

//--------------------------------------------------------------------
// These additional #define statements are required.

define ENCRYPT_ALGORITHM CALG_RC4

define ENCRYPT_BLOCK_SIZE 8

// Declare the function EncryptFile. The function definition
// follows main.

BOOL EncryptFile(
PCHAR szSource,
PCHAR szDestination,
PCHAR szPassword);

//--------------------------------------------------------------------
// Begin main.

void main(void)
{
CHAR szSource[100];
CHAR szDestination[100];
CHAR szPassword[100];

printf("Encrypt a file. \n\n");
printf("Enter the name of the file to be encrypted: ");
scanf("%s",szSource);
printf("Enter the name of the output file: ");
scanf("%s",szDestination);
printf("Enter the password:");
scanf("%s",szPassword);

//--------------------------------------------------------------------
// Call EncryptFile to do the actual encryption.

if(EncryptFile(szSource, szDestination, szPassword))
{
	printf("Encryption of the file %s was a success. \n", szSource);
	printf("The encrypted data is in file %s.\n",szDestination);
}
else
{
	HandleError("Error encrypting file!"); 
} 

} // End of main

//--------------------------------------------------------------------
// Code for the function EncryptFile called by main.

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.

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
{
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。会话密钥只能存在于一个会话过程）

//--------------------------------------------------------------------
// 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
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

//--------------------------------------------------------------------
// This example uses the function HandleError, a simple error
// handling function, to print an error message to the standard error
// (stderr) file and exit the program.
// For most applications, replace this function with one
// that does more extensive error reporting.

void HandleError(char *s)
{
fprintf(stderr,"An error occurred in running the program. \n");
fprintf(stderr,"%s\n",s);
fprintf(stderr, "Error number %x.\n", GetLastError());
fprintf(stderr, "Program terminating. \n");
exit(1);
} // End of HandleError`

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