Example C Program: Duplicating a Hash

The following example creates and duplicates a hash of some text. It then adds additional text to the original hash and different text to the duplicate.

This example uses the following CryptoAPI functions:

• CryptAcquireContext
• CryptCreateHash
• CryptHashData
• CryptDuplicateHash
• CryptGetHashParam
• CryptDestroyHash
• CryptReleaseContext

This example uses the function MyHandleError. Code for this function is included at the end of the example. Code for this and other auxiliary functions is also listed under General Purpose Functions.

#pragma comment(lib, "crypt32.lib")

#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#define MY_ENCODING_TYPE  (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
void MyHandleError(char *s);
void Get_And_Print_Hash(HCRYPTHASH hHash);

void main(void)
{
    //--------------------------------------------------------------------
    // Copyright (C) Microsoft.  All rights reserved.
    // Declare and initialize variables.
    HCRYPTPROV   hCryptProv = NULL;
    HCRYPTHASH   hOriginalHash;
    HCRYPTHASH   hDuplicateHash;

    //--------------------------------------------------------------------
    // Acquire a cryptographic provider context handle.
    if(CryptAcquireContext(
       &hCryptProv,
       NULL,
       NULL,
       PROV_RSA_FULL,
       0))
    {
        printf("CryptAcquireContext succeeded. \n");
    }
    else
    {
        MyHandleError("Error during CryptAcquireContext!");
    }

    //--------------------------------------------------------------------
    // Create a hash.
    if (CryptCreateHash(
        hCryptProv,
        CALG_SHA1,
        0,
        0,
        &hOriginalHash))
    {
       printf("An empty hash object has been created. \n");
    }
    else
    {
       MyHandleError("Error during CryptCreateHash.");
    }

    //--------------------------------------------------------------------
    // Hash a BYTE string.
    if (CryptHashData(
        hOriginalHash,
        (BYTE*)"Some Common Data",
        sizeof("Some Common Data"), 0))
    {
       printf("An original hash has been created. \n");
    }
    else
    {
       MyHandleError("Error during CryptHashData.");
    }

    //--------------------------------------------------------------------
    // Duplicate the hash.
    if (CryptDuplicateHash(
       hOriginalHash,
       NULL,
       0,
       &hDuplicateHash))
    {
       printf("The hash has been duplicated. \n");
    }
    else
    {
       MyHandleError("Error during CryptDuplicateHash.");
    }

    printf("The original hash -- phase 1.\n");
    Get_And_Print_Hash(hOriginalHash);

    printf("The duplicate hash -- phase 1.\n");
    Get_And_Print_Hash(hDuplicateHash);

    //--------------------------------------------------------------------
    // Hash some data with the original hash.
    if (CryptHashData(
         hOriginalHash,
         (BYTE*)"Some Data",
         sizeof("Some Data"),
         0))
    {
        printf("Additional data has been hashed with the original. \n");
    }
    else
    {
        MyHandleError("Error during CryptHashData.");
    }

    //--------------------------------------------------------------------
    // Hash other data with the duplicate hash.
    if (CryptHashData(
         hDuplicateHash,
         (BYTE*)"Other Data",
         sizeof("Other Data"),
         0))
    {
       printf("More data has been hashed with the duplicate. \n");
    }
    else
    {
       MyHandleError("Error during CryptHashData.");
    }

    printf("The original hash -- phase 2.\n");
    Get_And_Print_Hash(hOriginalHash);

    printf("The duplicate hash -- phase 2.\n");
    Get_And_Print_Hash(hDuplicateHash);

    // Destroy the original hash.
    if(CryptDestroyHash(hOriginalHash))
    {
       printf("The original hash has been destroyed. \n");
    }
    else
    {
       MyHandleError("ERROR during CryptDestroyHash");
    }

    //--------------------------------------------------------------------
    // Destroy the duplicate hash.
    if (CryptDestroyHash(hDuplicateHash))
    {
       printf("The duplicate hash has been destroyed. \n");
    }
    else
    {
       MyHandleError("Error -- CryptDestroyHash");
    }

    //--------------------------------------------------------------------
    // Release the CSP.

    if(hCryptProv)
       CryptReleaseContext(hCryptProv,0);

    printf("The program ran to completion without error. \n");
} // end main

//--------------------------------------------------------------------
// Define the function Get_And_Print_Hash.
void Get_And_Print_Hash(HCRYPTHASH hOHash)
{
    //--------------------------------------------------------------------
    // Declare and initialize local variables.
    HCRYPTHASH   hHash;
    BYTE         *pbHash;
    DWORD        dwHashLen;
    DWORD        dwHashLenSize = sizeof(DWORD);
    DWORD        i;

    //--------------------------------------------------------------------
    // Duplicate the hash passed in.
    // The hash is duplicated to leave the original hash intact.

    if (CryptDuplicateHash(
       hOHash,
       NULL,
       0,
       &hHash))
    {
        // It worked. Do nothing.
    }
    else
    {
       MyHandleError("Error during CryptDuplicateHash.");
    }

    if(CryptGetHashParam(
       hHash,
       HP_HASHSIZE,
       (BYTE *)&dwHashLen,
       &dwHashLenSize,
       0))
    {
        // It worked. Do nothing.
    }
    else
    {
        MyHandleError("CryptGetHashParam failed to get size.");
    }

    if(pbHash = (BYTE*)malloc(dwHashLen))
    {
        // It worked. Do nothing.
    }
    else
    {
         MyHandleError("Allocation failed.");
    }

    if(CryptGetHashParam(
       hHash,
       HP_HASHVAL,
       pbHash,
       &dwHashLen,
       0))
    {
        // Print the hash value.
        printf("The hash is:  ");
        for(i = 0 ; i < dwHashLen ; i++)
        {
           printf("%02x ",pbHash[i]);
        }
        printf("\n");
    }
    else
    {
        MyHandleError("Error during reading hash value.");
    }

    free(pbHash);
    if (CryptDestroyHash(hHash))
    {
        // It worked. Do nothing.
    }
    else
    {
       MyHandleError("ERROR - CryptDestroyHash");
    }
} // end Get_And_Print_Hash


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

void MyHandleError(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 MyHandleError