The CryptGetHashParam function lets applications retrieve data that governs of the operations of a hash object. The actual hash value can also be retrieved using this function.
BOOL CRYPTFUNC CryptGetHashParam(
HCRYPTHASH hHash, | |
DWORD dwParam, | |
BYTE *pbData, | |
DWORD *pdwDataLen, | |
DWORD dwFlags | |
); |
This parameter can be NULL if all you are doing is determining the number of
bytes required for the returned parameter data.
If the buffer specified by pbData is not large enough to hold the data, the function returns the ERROR_MORE_DATA error code (through GetLastError), and stores the required buffer size, in bytes, in the variable pointed to by pdwDataLen.
If pbData is NULL, then no error is returned and the function stores
the size of the data, in bytes, in the variable pointed to by pdwDataLen.
The dwParam value can be set to one of the following hash parameter types:
Applications should retrieve this parameter just before the HP_HASHVAL
parameter so the correct amount of memory can be allocated.
Once this parameter has been retrieved, the hash object is marked “finished” and no more data can be added to it.
Note that some CSPs may add additional parameters that can be queried through this function.
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To retrieve extended error information, use the GetLastError function.
The following table lists the error codes most commonly returned by the GetLastError function. The error codes tat prefaced by “NTE” are generated by the particular CSP you are using.
Error |
Description |
ERROR_INVALID_HANDLE |
One of the parameters specifies an invalid handle. |
ERROR_INVALID_PARAMETER |
One of the parameters contains an invalid value. This is most often an illegal pointer. |
NTE_BAD_FLAGS |
The dwFlags parameter is nonzero. |
NTE_BAD_HASH |
The hash object specified by the hHash parameter is invalid. |
NTE_BAD_TYPE |
The dwParam parameter specifies an unknown parameter number. |
NTE_BAD_UID |
The CSP context that was specified when the hash was created cannot be found. |
#include <wincrypt.h> HCRYPTPROV hProv = 0; HCRYPTHASH hHash = 0; BYTE *pbHash = NULL; DWORD dwHashLen; #define BUFFER_SIZE 256 BYTE pbBuffer[BUFFER_SIZE]; DWORD dwCount; DWORD i; // Get handle to the default provider. if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)) { printf("Error %x during CryptAcquireContext!\n", GetLastError()); goto done; } // Create hash object. if(!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) { printf("Error %x during CryptBeginHash!\n", GetLastError()); goto done; } // Fill buffer with test data. for(i = 0 ; i < BUFFER_SIZE ; i++) { pbBuffer[i] = (BYTE)i; } // Hash in buffer. if(!CryptHashData(hHash, pbBuffer, BUFFER_SIZE, 0)) { printf("Error %x during CryptHashData!\n", GetLastError()); goto done; } // Read hash value size and allocate memory. dwCount = sizeof(DWORD); if(!CryptGetHashParam(hHash, HP_HASHSIZE, (BYTE *)&dwHashLen, &dwCount, 0)) { printf("Error %x during reading hash size!\n", GetLastError()); goto done; } if((pbHash = malloc(dwHashLen)) == NULL) { printf("Out of memory!\n"); goto done; } // Read hash value. if(!CryptGetHashParam(hHash, HP_HASHVAL, pbHash, &dwHashLen, 0)) { printf("Error %x during reading hash value!\n", GetLastError()); goto done; } // Print hash value. for(i = 0 ; i < dwHashLen ; i++) { printf("%2.2x ",pbHash[i]); } printf("\n"); done: // Free memory. if(pbHash !=NULL) free(pbHash); // Destroy hash object. if(hHash) CryptDestroyHash(hHash); // Release CSP handle. if(hProv) CryptReleaseContext(hProv,0);
CryptCreateHash, CryptGetKeyParam, CryptHashData, CryptHashSessionKey, CryptSetHashParam
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