computing hashValue of a file - visual-studio-2010

Question

Small piece of code I wrote to list files in a dummy directory and then calculate the hash values.
But when I pass the filename to the calc_hash function , program terminates after computing the hash of two files... with error Unhandled exception at 0x77406850 in hashtest3-cpp.exe: 0xC0000005: Access violation writing location 0x64333782.
Can someone please point out the error ....
code snippet::
#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#include <strsafe.h>
#include <string.h>
#include <tchar.h>
#include <iostream>
using namespace std;
#define BUFSIZE 1024
#define MD5LEN 16
//======================================================VARIABLE INITIALIZATION
DWORD Status = 0;
BOOL bResult = FALSE;
ULONG_PTR hProv = 0;
ULONG_PTR hHash = 0;
HANDLE hFile = NULL;
DWORD i;
DWORD j=0;
BYTE rgbFile[BUFSIZE];
DWORD cbRead = 0;
BYTE rgbHash[MD5LEN];
DWORD cbHash = 0;
LPTSTR filename;
CHAR resultstream[33];
HANDLE hFind;
WIN32_FIND_DATA data;
TCHAR filepath[260] = _T("");
LPWSTR FNAME;
LPWSTR FULLPATH = L"c:\\test\\";
LPWSTR dir = L"c:\\test\\*.*";
LPWSTR DEFAULt = L"";
CHAR rgbDigits[] = "0123456789abcdef";
//=====================================================FUNCTION DECLARATION
void list_files(void);
void calc_hash(void);
//======================================================MAIN START
int main()
{
list_files();
//calc_hash();
getchar();
return 0;
}
//======================================================LISTING FILES IN A DIRECTORY
void list_files()
{
hFind = FindFirstFile(dir, &data);
if (hFind != INVALID_HANDLE_VALUE)
{
do
{
StringCchCopy(filepath, 260, DEFAULt);
resultstream[33] = '\0';
DWORD j=0;
FNAME = data.cFileName;
StringCchCat(filepath, 260, FULLPATH);
StringCchCat(filepath, 260, FNAME);
filename = (LPTSTR)filepath;
printf("\n%ws", filename);
/*calc_hash();
getchar();*/
continue;
}while (FindNextFile(hFind, &data));
}
getchar();
}
//======================================================HASH OF A FILE
void calc_hash()
{
hFile = CreateFile(
filename,
GENERIC_READ,
FILE_SHARE_READ,
NULL,
OPEN_EXISTING,
FILE_FLAG_SEQUENTIAL_SCAN,
NULL
);
if (INVALID_HANDLE_VALUE == hFile)
{
Status = GetLastError();
//printf("\nerror opening file::%d", Status);
goto end;
}
// Get handle to the crypto provider
if (!CryptAcquireContext(
&hProv,
NULL,
NULL,
PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT))
{
Status = GetLastError();
printf("CryptAcquireContext error:: %d\n", Status);
CloseHandle(hFile);
getchar();
goto end;
}
if (!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash))
{
Status = GetLastError();
printf("CryptAcquireContext error:: %d\n", Status);
CloseHandle(hFile);
CryptReleaseContext(hProv, 0);
getchar();
goto end;
}
while (bResult = ReadFile(hFile, rgbFile, BUFSIZE, &cbRead, NULL))
{
if (0 == cbRead)
{
break;
}
if (!CryptHashData(hHash, rgbFile, cbRead, 0))
{
Status = GetLastError();
printf("CryptHashData error:: %d\n", Status);
CryptReleaseContext(hProv, 0);
CryptDestroyHash(hHash);
CloseHandle(hFile);
getchar();
goto end;
}
}
//================================GENERATING RESULT=============================
if (!bResult)
{
Status = GetLastError();
printf("ReadFile error:%S:: %d\n",filename, Status);
CryptReleaseContext(hProv, 0);
CryptDestroyHash(hHash);
CloseHandle(hFile);
getchar();
goto end;
}
cbHash = MD5LEN;
if (CryptGetHashParam(hHash, HP_HASHVAL, rgbHash, &cbHash, 0))
{
printf("MD5 hash of file %ws is:- ", filename);
for (i = 0; i < cbHash; i++)
{
resultstream[j]=rgbDigits[rgbHash[i] >> 4];
j++;
resultstream[j]=rgbDigits[rgbHash[i] & 0xf];
j++;
}
resultstream[j] = '\0';
printf("\n%s", resultstream );
printf("\n");
}
else
{
Status = GetLastError();
printf("CryptGetHashParam error:: %d\n", Status);
}
CryptDestroyHash(hHash);
CryptReleaseContext(hProv, 0);
CloseHandle(hFile);
end:;
//getchar();
}

Answer 1

The problem is you declare resultstream as
CHAR resultstream[33];
but then you use in your code
resultstream[33] = '\0';
The resultstream array is 0 indexed so valid values are 0-32, you are accessing memory not allocated for that array (hence the "Access violation")