C++ PBKDF2 Issue

Question

I have the following function:

void PBKDF2_HMAC_SHA_512_string(const char* pass, const char* salt, int32_t iterations, uint32_t HashLength, char* out) {
    unsigned int i;
    HashLength = HashLength / 2;
    unsigned char* digest = new unsigned char[HashLength];
    PKCS5_PBKDF2_HMAC(pass, strlen(pass), (const unsigned char*)salt, strlen(salt), iterations, EVP_sha512(), HashLength, digest);
    for (i = 0; i < sizeof(digest); i++) {
        sprintf(out + (i * 2), "%02x", 255 & digest[i]);
    }
}

When I call the function like below, I expect to get a hash back of 2400 in length, however it returns me 16:

char PBKDF2Hash[1025]; //\0 terminating space?
memset(PBKDF2Hash, 0, sizeof(PBKDF2Hash));
PBKDF2_HMAC_SHA_512_string("Password", "0123456789123456", 3500, 1024, PBKDF2Hash);
//PBKDF2Hash is now always 16 long -> strlen(PBKDF2Hash),
//while I expect it to be 2400 long?
//How is this possible and why is this happening?
//I can't figure it out

Answer 1

Since digest is a pointer, sizeof(digest) will not give the length of the array. Depending on different platforms, sizeof(digest) may give you 4 or 8, which is not what you want. Maybe you should use for (i = 0; i < HashLength; i++).

Another unrelated issue of your code is that, digest is not deleted in PBKDF2_HMAC_SHA_512_string, which causes memory leak