Is it possible to do a HMAC with wincrypt?

Question

I\'ve been trying to perform a straight forward SHA256 HMAC using wincrypt/cryptoapi/Cryptography API: Next Generation (CNG) and i\'m really struggling. My target is Windows

Answer 1

Thank you for the information Mgetz. I never knew about the BCrypt set of methods. It is a lot easier for HMAC than CryptHashData of the wincrypt/cryptoapi. From the example of using hashing using SHA256 I was able to create the HMAC code. You only need to add BCRYPT_ALG_HANDLE_HMAC_FLAG to the last parameter of BCryptOpenAlgorithmProvider and include the key in the call to BCryptCreateHash.

This is the completed code:

#include <windows.h>
#include <stdio.h>
#include <bcrypt.h>
#pragma comment(lib, "bcrypt.lib") 
#define NT_SUCCESS(Status)          (((NTSTATUS)(Status)) >= 0)

#define STATUS_UNSUCCESSFUL         ((NTSTATUS)0xC0000001L)

void __cdecl wmain(
    int                      argc,
    __in_ecount(argc) LPWSTR *wargv)
{
    BCRYPT_ALG_HANDLE       hAlg = NULL;
    BCRYPT_HASH_HANDLE      hHash = NULL;
    NTSTATUS                status = STATUS_UNSUCCESSFUL;
    DWORD                   cbData = 0,
        cbHash = 0,
        cbHashObject = 0;
    PBYTE                   pbHashObject = NULL;
    PBYTE                   pbHash = NULL;
    CONST BYTE key[] = { "SecretKey" };
    CONST BYTE message[] = { "<SomeXmlData />" };

    //open an algorithm handle
    if (!NT_SUCCESS(status = BCryptOpenAlgorithmProvider(
        &hAlg,
        BCRYPT_SHA256_ALGORITHM,
        NULL,
        BCRYPT_ALG_HANDLE_HMAC_FLAG)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptOpenAlgorithmProvider\n", status);
        goto Cleanup;
    }

    //calculate the size of the buffer to hold the hash object
    if (!NT_SUCCESS(status = BCryptGetProperty(
        hAlg,
        BCRYPT_OBJECT_LENGTH,
        (PBYTE)&cbHashObject,
        sizeof(DWORD),
        &cbData,
        0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptGetProperty\n", status);
        goto Cleanup;
    }

    //allocate the hash object on the heap
    pbHashObject = (PBYTE)HeapAlloc(GetProcessHeap(), 0, cbHashObject);
    if (NULL == pbHashObject)
    {
        wprintf(L"**** memory allocation failed\n");
        goto Cleanup;
    }

    //calculate the length of the hash
    if (!NT_SUCCESS(status = BCryptGetProperty(
        hAlg,
        BCRYPT_HASH_LENGTH,
        (PBYTE)&cbHash,
        sizeof(DWORD),
        &cbData,
        0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptGetProperty\n", status);
        goto Cleanup;
    }

    //allocate the hash buffer on the heap
    pbHash = (PBYTE)HeapAlloc(GetProcessHeap(), 0, cbHash);
    if (NULL == pbHash)
    {
        wprintf(L"**** memory allocation failed\n");
        goto Cleanup;
    }

    //create a hash
    if (!NT_SUCCESS(status = BCryptCreateHash(
        hAlg,
        &hHash,
        pbHashObject,
        cbHashObject,
        (PBYTE)key,
        sizeof(key)-1,
        0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptCreateHash\n", status);
        goto Cleanup;
    }

    //hash some data
    if (!NT_SUCCESS(status = BCryptHashData(
        hHash,
        (PBYTE)message,
        sizeof(message)-1,
        0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptHashData\n", status);
        goto Cleanup;
    }

    //close the hash
    if (!NT_SUCCESS(status = BCryptFinishHash(
        hHash,
        pbHash,
        cbHash,
        0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptFinishHash\n", status);
        goto Cleanup;
    }

    printf("The hash is:  ");
    for (DWORD i = 0; i < cbHash; i++)
    {
        printf("%2.2X-", pbHash[i]);
    }


Cleanup:

    if (hAlg)
    {
        BCryptCloseAlgorithmProvider(hAlg, 0);
    }

    if (hHash)
    {
        BCryptDestroyHash(hHash);
    }

    if (pbHashObject)
    {
        HeapFree(GetProcessHeap(), 0, pbHashObject);
    }

    if (pbHash)
    {
        HeapFree(GetProcessHeap(), 0, pbHash);
    }
};