哈希消息身份验证校验和（HMAC）通常用于验证传输期间消息是否已更改。 消息的双方必须具有共享的密钥。 发送方将密钥和消息合并为字符串，使用 SHA-1 或 MD5 等算法创建字符串摘要，并传输消息和摘要。 接收方将共享密钥与消息组合在一起，应用适当的算法，并比较发送方传输的摘要。 如果摘要完全相同，则消息不会被篡改。
此示例演示了以下任务和 CryptoAPI 函数：
- 通过调用 CryptAcquireContext，获取对 加密服务提供商 的句柄。
- 通过调用 CryptCreateHash、CryptHashData和 CryptDeriveKey，从字节字符串派生对称密钥。
- 使用对称密钥通过调用 CryptCreateHash 和 CryptSetHashParam来创建 HMAC 哈希对象。
- 通过调用 CryptHashData对消息进行哈希处理。
- 通过调用 <
CryptGetHashParam
#include <stdio.h>
#include <windows.h>
#include <wincrypt.h>
int main()
{
//--------------------------------------------------------------------
// Declare variables.
//
// hProv: Handle to a cryptographic service provider (CSP).
// This example retrieves the default provider for
// the PROV_RSA_FULL provider type.
// hHash: Handle to the hash object needed to create a hash.
// hKey: Handle to a symmetric key. This example creates a
// key for the RC4 algorithm.
// hHmacHash: Handle to an HMAC hash.
// pbHash: Pointer to the hash.
// dwDataLen: Length, in bytes, of the hash.
// Data1: Password string used to create a symmetric key.
// Data2: Message string to be hashed.
// HmacInfo: Instance of an HMAC_INFO structure that contains
// information about the HMAC hash.
//
HCRYPTPROV hProv = NULL;
HCRYPTHASH hHash = NULL;
HCRYPTKEY hKey = NULL;
HCRYPTHASH hHmacHash = NULL;
PBYTE pbHash = NULL;
DWORD dwDataLen = 0;
BYTE Data1[] = {0x70,0x61,0x73,0x73,0x77,0x6F,0x72,0x64};
BYTE Data2[] = {0x6D,0x65,0x73,0x73,0x61,0x67,0x65};
HMAC_INFO HmacInfo;
//--------------------------------------------------------------------
// Zero the HMAC_INFO structure and use the SHA1 algorithm for
// hashing.
ZeroMemory(&HmacInfo, sizeof(HmacInfo));
HmacInfo.HashAlgid = CALG_SHA1;
//--------------------------------------------------------------------
// Acquire a handle to the default RSA cryptographic service provider.
if (!CryptAcquireContext(
&hProv, // handle of the CSP
NULL, // key container name
NULL, // CSP name
PROV_RSA_FULL, // provider type
CRYPT_VERIFYCONTEXT)) // no key access is requested
{
printf(" Error in AcquireContext 0x%08x \n",
GetLastError());
goto ErrorExit;
}
//--------------------------------------------------------------------
// Derive a symmetric key from a hash object by performing the
// following steps:
// 1. Call CryptCreateHash to retrieve a handle to a hash object.
// 2. Call CryptHashData to add a text string (password) to the
// hash object.
// 3. Call CryptDeriveKey to create the symmetric key from the
// hashed password derived in step 2.
// You will use the key later to create an HMAC hash object.
if (!CryptCreateHash(
hProv, // handle of the CSP
CALG_SHA1, // hash algorithm to use
0, // hash key
0, // reserved
&hHash)) // address of hash object handle
{
printf("Error in CryptCreateHash 0x%08x \n",
GetLastError());
goto ErrorExit;
}
if (!CryptHashData(
hHash, // handle of the hash object
Data1, // password to hash
sizeof(Data1), // number of bytes of data to add
0)) // flags
{
printf("Error in CryptHashData 0x%08x \n",
GetLastError());
goto ErrorExit;
}
if (!CryptDeriveKey(
hProv, // handle of the CSP
CALG_RC4, // algorithm ID
hHash, // handle to the hash object
0, // flags
&hKey)) // address of the key handle
{
printf("Error in CryptDeriveKey 0x%08x \n",
GetLastError());
goto ErrorExit;
}
//--------------------------------------------------------------------
// Create an HMAC by performing the following steps:
// 1. Call CryptCreateHash to create a hash object and retrieve
// a handle to it.
// 2. Call CryptSetHashParam to set the instance of the HMAC_INFO
// structure into the hash object.
// 3. Call CryptHashData to compute a hash of the message.
// 4. Call CryptGetHashParam to retrieve the size, in bytes, of
// the hash.
// 5. Call malloc to allocate memory for the hash.
// 6. Call CryptGetHashParam again to retrieve the HMAC hash.
if (!CryptCreateHash(
hProv, // handle of the CSP.
CALG_HMAC, // HMAC hash algorithm ID
hKey, // key for the hash (see above)
0, // reserved
&hHmacHash)) // address of the hash handle
{
printf("Error in CryptCreateHash 0x%08x \n",
GetLastError());
goto ErrorExit;
}
if (!CryptSetHashParam(
hHmacHash, // handle of the HMAC hash object
HP_HMAC_INFO, // setting an HMAC_INFO object
(BYTE*)&HmacInfo, // the HMAC_INFO object
0)) // reserved
{
printf("Error in CryptSetHashParam 0x%08x \n",
GetLastError());
goto ErrorExit;
}
if (!CryptHashData(
hHmacHash, // handle of the HMAC hash object
Data2, // message to hash
sizeof(Data2), // number of bytes of data to add
0)) // flags
{
printf("Error in CryptHashData 0x%08x \n",
GetLastError());
goto ErrorExit;
}
//--------------------------------------------------------------------
// Call CryptGetHashParam twice. Call it the first time to retrieve
// the size, in bytes, of the hash. Allocate memory. Then call
// CryptGetHashParam again to retrieve the hash value.
if (!CryptGetHashParam(
hHmacHash, // handle of the HMAC hash object
HP_HASHVAL, // query on the hash value
NULL, // filled on second call
&dwDataLen, // length, in bytes, of the hash
0))
{
printf("Error in CryptGetHashParam 0x%08x \n",
GetLastError());
goto ErrorExit;
}
pbHash = (BYTE*)malloc(dwDataLen);
if(NULL == pbHash)
{
printf("unable to allocate memory\n");
goto ErrorExit;
}
if (!CryptGetHashParam(
hHmacHash, // handle of the HMAC hash object
HP_HASHVAL, // query on the hash value
pbHash, // pointer to the HMAC hash value
&dwDataLen, // length, in bytes, of the hash
0))
{
printf("Error in CryptGetHashParam 0x%08x \n", GetLastError());
goto ErrorExit;
}
// Print the hash to the console.
printf("The hash is: ");
for(DWORD i = 0 ; i < dwDataLen ; i++)
{
printf("%2.2x ",pbHash[i]);
}
printf("\n");
// Free resources.
ErrorExit:
if(hHmacHash)
CryptDestroyHash(hHmacHash);
if(hKey)
CryptDestroyKey(hKey);
if(hHash)
CryptDestroyHash(hHash);
if(hProv)
CryptReleaseContext(hProv, 0);
if(pbHash)
free(pbHash);
return 0;
}