Paste TOTP directly to the console with a hotkey in windows

totp_paster_win32.cpp

#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctime>
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <string>

#include <windows.h>
#include <shobjidl.h>
#include <objbase.h>
#include <sal.h>

#include <stdarg.h>
#include <wchar.h>
#include <thread>

#pragma comment(lib, "ws2_32.lib")
#pragma comment (lib, "crypt32")

const char* base32 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";

// Modified from https://github.com/arachsys/totp
std::string generate_totp() {

  int64_t offset;
  size_t keysize, length;
  uint8_t digits, * hmac, key[64], msg[8];
  uint32_t bits, code, count;
  uint64_t clock, interval;
  unsigned int hmacsize;
  const EVP_MD* digest;

  keysize = 0;

  char out[100];

  const char* secret = "TOTP_SECRET_KEY ";

  digest = EVP_sha1();

  for (count = bits = length = 0; *secret; secret++) {
    if (!strchr(base32, *secret))
      break;
    bits = (bits << 5) | (strchr(base32, *secret) - base32);
    count += 5;

    while (count >= 8) {
      while (length >= keysize) {
        keysize = keysize ? keysize << 1 : 64;
        if (keysize>64)
          return "";
      }
      count -= 8, key[length++] = bits >> count;
    }
  }

  offset = 0;

  if (length > 0) {
    clock = (time(NULL) - offset) / 30;
    for (count = 0; count < 8; count++)
      msg[7 - count] = clock >> 8 * count;
    hmac = HMAC(digest, key, length, msg, sizeof(msg), NULL, &hmacsize);

    for (code = count = 0; count < 4; count++)
      code += hmac[(hmac[hmacsize - 1] & 0x0f) + 3 - count] << 8 * count;
    code &= 0x7fffffff;

    sprintf_s(out,"%06u", code % 1000000);
  }
  out[6] = '\0'; // Force null byte to end the 6 digits
  std::string output(out);

  return output;
}


bool KeyPress(UINT key)
{
  INPUT inputs[2];
  ZeroMemory(inputs, sizeof(inputs));

  inputs[0].type = INPUT_KEYBOARD;
  inputs[0].ki.wVk = key;

  inputs[1].type = INPUT_KEYBOARD;
  inputs[1].ki.wVk = key;
  inputs[1].ki.dwFlags = KEYEVENTF_KEYUP;


  SendInput(ARRAYSIZE(inputs), inputs, sizeof(INPUT));

  return true;

}

bool send_otp() {
  std::string totp = generate_totp();
  
  INPUT inputs[2];
  ZeroMemory(inputs, sizeof(inputs));

  // CTRL up before the input
  inputs[0].type = INPUT_KEYBOARD;
  inputs[0].ki.wVk = VK_LCONTROL;
  inputs[0].ki.dwFlags = KEYEVENTF_KEYUP;

  inputs[1].type = INPUT_KEYBOARD;
  inputs[1].ki.wScan = ::MapVirtualKey(LOBYTE(VkKeyScan('1')), MAPVK_VK_TO_VSC);  
  inputs[1].ki.dwFlags = KEYEVENTF_SCANCODE | KEYEVENTF_KEYUP;

  UINT uSent = SendInput(ARRAYSIZE(inputs), inputs, sizeof(INPUT));

  for (char key : totp) {
    if (key >= '0' && key <= '9') { // Force only numbers
      //const SHORT Vk = VkKeyScan(key);
      //const UINT VKey = ::MapVirtualKey(LOBYTE(Vk), MAPVK_VK_TO_VSC);
      KeyPress((key-'0') + 0x30); // Map ASCII to Windows virtual keys
      Sleep(2);
    }
  }

  return true;
}

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    if (RegisterHotKey(NULL, 1, MOD_CONTROL, 0x31))   // CTRL+1
    {
      // Done
    }
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
      if (msg.message == WM_HOTKEY)
      {        
        send_otp();
      }
    }

    return 0;
}