c - hashResult 变量没有存储正确的值

Question

我有一个从文件生成散列键的程序。例如，程序的结果是 "hash of file c:\Users\Jax\Desktop\files\file.txt is: 4db5a10d2ea73e3f76"。

我有一个变量，它具有此 file.txt 的预期哈希值:

char hashExpected   = "4db5a10d2ea73e3f76";

在代码的特定部分，我正在验证程序的结果哈希值是否等于存储在 hashExpected 变量中的哈希值。我有这个像下面。我有 hashResult 变量存储结果哈希，这样我就可以进行比较。但它不能正常工作，因为它总是显示 Hash is different 即使它是相等的。 hashResult 变量似乎没有存储正确的值。

        for (i = 0; i < cbHash; i++)
        {
            printf("%c%c",
                   rgbDigits[rgbHash[i] >> 4],
                   rgbDigits[rgbHash[i] & 0xf]);
            hashResult[i] = rgbDigits[rgbHash[i] >> 4];
            hashResult[i] += rgbDigits[rgbHash[i] & 0xf];
        }
        if (verify(hashResult, hashExpected))
        {
            printf("Hash is the same\n");
        }
        else
        {
            printf("Hash is different\n");
        }

完整程序:

#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#include <stdbool.h>
#define BUFSIZE 1024
#define MD5LEN  16

bool verify(char array1[], char array2[])
{
    int i;
    for (i = 0; array1[i] && array2[i]; ++i)
    {
        if (array1[i] != array2[i])
        {
            return false;
        }
    }
    return true;
}
DWORD main()
{
    DWORD dwStatus = 0;
    BOOL bResult = FALSE;
    HCRYPTPROV hProv = 0;
    HCRYPTHASH hHash = 0;
    HANDLE hFile = NULL;
    BYTE rgbFile[BUFSIZE];
    DWORD cbRead = 0;
    BYTE rgbHash[MD5LEN];
    DWORD cbHash = 0;
    CHAR rgbDigits[] = "0123456789abcdef";
    PCSTR filename = "c:\\Users\\Jax\\Desktop\\files\\file.txt";
    char hashActual[]   = "4db5a10d2ea73e3f76";
    char hashExpected[] = "4db5a10d2ea73e3f76";
    char hashWrong[]    = "0a0a0a0a0a0a0a";
    char hashResult[] = "";
    hFile = CreateFile(filename,
                       GENERIC_READ,
                       FILE_SHARE_READ,
                       NULL,
                       OPEN_EXISTING,
                       FILE_FLAG_SEQUENTIAL_SCAN,
                       NULL);


    if (INVALID_HANDLE_VALUE == hFile)
    {
        dwStatus = GetLastError();
        printf("Error opening file %s\nError: %d\n", filename,
               dwStatus);
        return dwStatus;
    }


    // Get handle to the crypto provider
    if (!CryptAcquireContext(&hProv,
                             NULL,
                             NULL,
                             PROV_RSA_FULL,
                             CRYPT_VERIFYCONTEXT))
    {
        dwStatus = GetLastError();
        printf("CryptAcquireContext failed: %d\n", dwStatus);
        CloseHandle(hFile);
        return dwStatus;
    }


    if (!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash))
    {
        dwStatus = GetLastError();
        printf("CryptAcquireContext failed: %d\n", dwStatus);
        CloseHandle(hFile);
        CryptReleaseContext(hProv, 0);
        return dwStatus;
    }


    while (bResult = ReadFile(hFile, rgbFile, BUFSIZE,
                              &cbRead, NULL))
    {
        if (0 == cbRead)
        {
            break;
        }


        if (!CryptHashData(hHash, rgbFile, cbRead, 0))
        {
            dwStatus = GetLastError();
            printf("CryptHashData failed: %d\n", dwStatus);
            CryptReleaseContext(hProv, 0);
            CryptDestroyHash(hHash);
            CloseHandle(hFile);
            return dwStatus;
        }
    }


    if (!bResult)
    {
        dwStatus = GetLastError();
        printf("ReadFile failed: %d\n", dwStatus);
        CryptReleaseContext(hProv, 0);
        CryptDestroyHash(hHash);
        CloseHandle(hFile);
        return dwStatus;
    }


    cbHash = MD5LEN;


    if (CryptGetHashParam(hHash, HP_HASHVAL, rgbHash, &cbHash, 0))
    {
        DWORD i;

        printf("MD5 hash of file %s is: ", filename);
        for (i = 0; i < cbHash; i++)
        {
            printf("%c%c",
                   rgbDigits[rgbHash[i] >> 4],
                   rgbDigits[rgbHash[i] & 0xf]);
            hashResult[i] = rgbDigits[rgbHash[i] >> 4];
            hashResult[i] += rgbDigits[rgbHash[i] & 0xf];


        }
        if (verify(hashResult, hashExpected))
        {
            printf("Hash is the same\n");
        }
        else
        {
            printf("Hash is different\n");
        }
    }
    else
    {
        dwStatus = GetLastError();
        printf("CryptGetHashParam failed: %d\n", dwStatus);
    }


    CryptDestroyHash(hHash);
    CryptReleaseContext(hProv, 0);
    CloseHandle(hFile);


    return dwStatus;
}

Answer 1

char hashExpected[] = "4db5a10d2ea73e3f76";

上面的MD5值是错误的。 MD5 值的长度为 16 个字节。但这只是字节数。我们不能在屏幕上打印字节，因此我们经常将字节转换为十六进制值。例如，如果我们有 unsinged char bytes[3] = {0x01,0x01,0xFF}，我们将字节转换为十六进制字符串，它变成 "0102FF"。

请注意，字符串表示形式加了一个空终止符两倍长。 MD5 散列的例子是:

"C4CA4238A0B923820DCC509A6F75849B"

字符串的缓冲区大小应为 33 (16 x 2 + 1)

要找到正确的 hashExpected，请搜索 “在线 MD5 计算器”。您可以使用http://onlinemd5.com/之类的网站来计算文件的MD5。

或者使用内容为1的文件。 MD5("1") 是 "C4CA4238A0B923820DCC509A6F75849B"，将其用作预期的哈希值。

char hashResult[] = "";

上面一行是一个编程错误，正如@melpomene 在评论中提到的

hashResult[i] = rgbDigits[rgbHash[i] >> 4];
hashResult[i] += rgbDigits[rgbHash[i] & 0xf];

上面的代码是错误的，你需要这个:

char hashResult[MD5LEN * 2 + 1] = "";
...
hashResult[i * 2] = rgbDigits[rgbHash[i] >> 4];
hashResult[i * 2 + 1] = rgbDigits[rgbHash[i] & 0xf];

verify 函数也存在问题，因为它比较错误的字节表示形式的 MD5 和错误的字符串表示形式的 MD5。

您可以使用strcmp 或_stricmp 来比较字符串表示中的MD5 值。或者使用memcmp(data1, data2, 16)直接比较字节。

完整示例:

#define BUFSIZE 1024
#define MD5LEN  16

int main()
{
    DWORD dwStatus = 0;
    HCRYPTPROV hProv = 0;
    HCRYPTHASH hHash = 0;
    HANDLE hFile = NULL;
    BYTE rgbFile[BUFSIZE];
    DWORD cbRead = 0;
    BYTE rgbHash[MD5LEN];
    DWORD cbHash = 0;
    CHAR rgbDigits[] = "0123456789abcdef";
    PCSTR filename = "c:\\Users\\Jax\\Desktop\\files\\file.txt";

    //assuming content of file.txt is '1'
    char hashExpected[] = "C4CA4238A0B923820DCC509A6F75849B"; 

    char hashResult[MD5LEN * 2 + 1] = "";
    hFile = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ,
        NULL, OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, NULL);

    if(INVALID_HANDLE_VALUE == hFile)
    {
        dwStatus = GetLastError();
        printf("Error opening file %s\nError: %d\n", filename, dwStatus);
        return (int)dwStatus;
    }

    // Get handle to the crypto provider
    if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
    {
        dwStatus = GetLastError();
        printf("CryptAcquireContext failed: %d\n", dwStatus);
        CloseHandle(hFile);
        return (int)dwStatus;
    }

    if(!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash))
    {
        dwStatus = GetLastError();
        printf("CryptAcquireContext failed: %d\n", dwStatus);
        CloseHandle(hFile);
        CryptReleaseContext(hProv, 0);
        return (int)dwStatus;
    }

    while(ReadFile(hFile, rgbFile, BUFSIZE, &cbRead, NULL))
    {
        if(0 == cbRead)
            break;

        if(!CryptHashData(hHash, rgbFile, cbRead, 0))
        {
            dwStatus = GetLastError();
            printf("CryptHashData failed: %d\n", dwStatus);
            CryptReleaseContext(hProv, 0);
            CryptDestroyHash(hHash);
            CloseHandle(hFile);
            return (int)dwStatus;
        }
    }

    cbHash = MD5LEN;

    if(CryptGetHashParam(hHash, HP_HASHVAL, rgbHash, &cbHash, 0))
    {
        DWORD i;

        printf("MD5 expected, versus MD5 of file %s is:\n", filename);
        printf("%s\n", hashExpected);
        for(i = 0; i < cbHash; i++)
        {
            printf("%c%c",
                rgbDigits[rgbHash[i] >> 4],
                rgbDigits[rgbHash[i] & 0xf]);
            hashResult[i * 2] = rgbDigits[rgbHash[i] >> 4];
            hashResult[i * 2 + 1] = rgbDigits[rgbHash[i] & 0xf];
        }
        printf("\n");

        if(_strcmpi(hashResult, hashExpected) == 0)
            printf("Hash is the same\n");
        else
            printf("Hash is different\n");
    }
    else
    {
        dwStatus = GetLastError();
        printf("CryptGetHashParam failed: %d\n", dwStatus);
    }

    CryptDestroyHash(hHash);
    CryptReleaseContext(hProv, 0);
    CloseHandle(hFile);

    return (int)dwStatus;
}