SHA1 hash using Windows APIs

sha1-windows.c

#include <Windows.h>
#include <Wincrypt.h>
#pragma comment(lib, "advapi32.lib")

#define SHA1LEN 20

// generates SHA1 hash and returns 20-byte heap-memory if successful, otherwise NULL
unsigned char* sha1(unsigned char* data, int len)
{
    HCRYPTPROV hProv = 0;
    HCRYPTHASH hHash = 0;
    BYTE* sha1sum;
    DWORD sha1len = SHA1LEN;
    BOOL hashCalculated;

    if (!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
        return NULL;
    
    if (!CryptCreateHash(hProv, CALG_SHA1, 0, 0, &hHash))
    {
        CryptReleaseContext(hProv, 0);
        return NULL;
    }

    if (!CryptHashData(hHash, data, len, 0))
    {
        CryptDestroyHash(hHash);
        CryptReleaseContext(hProv, 0);
        return NULL;
    }

    sha1sum = (BYTE*)malloc(SHA1LEN);
    hashCalculated = CryptGetHashParam(hHash, HP_HASHVAL, sha1sum, &sha1len, 0);
    CryptDestroyHash(hHash);
    CryptReleaseContext(hProv, 0);

    if (hashCalculated)        
        return sha1sum;
    else
    {
        free(sha1sum);
        return NULL;
    }
}

int main()
{
    char text[] = "abcd";
    unsigned char* sha1sum = sha1((BYTE*)text, strlen(text));
    // use the hash here
    
    // when you're done with the hash, free the memory
    free(sha1sum);
    
    return 0;
}