B4R Tutorial ESP32: OTP/2FA example

This example generates a OTP/2FA ("One Time Password") as you know it when you login to a website and you get a 6 digit code via sms. It changes every 30 seconds.

How it works:

- as it is time based, you need a internet connection. Please add your wifi/router credentials
- time is retrieved from pool.ntp.org (please change the time offset to your country/timezone)
- the time is converted in a unixtimestamp
- it is converted to hex and filled up with leading zeroes giving a total length of 16
- these 16 bytes are HMAC-SHA1 hashed with a secret (both sides must use the same secret)
- with the help of some bit operations (shift/and/or) plus a power/modulus calculation we finally get the OTP code

B4x example with integration in Google Authenticator: OTP

#Region Project Attributes
    #AutoFlushLogs: True
    #CheckArrayBounds: True
    #StackBufferSize: 1000

#End Region
'Ctrl+Click to open the C code folder: ide://run?File=%WINDIR%\System32\explorer.exe&Args=%PROJECT%\Objects\Src

Sub Process_Globals
    Public Serial1 As Serial
    
    Private bc As ByteConverter
    
    Private WiFi As ESP8266WiFi
    Private SSID As String=""
    Private SSIDPW As String=""

    Private hmackey(255) As Byte
    Private hmackey_len As ULong
    Private hmacpayload(255) As Byte
    Private hmacpayload_len As ULong
    Private hmacbytessha1(20) As Byte
    Private hmacbytessha256(64) As Byte
    
    Private TimeVar(100) As Byte
    Private unixtimestamp As Long
    Private uthex(20) As Byte
    
    Dim p1,p2,p3,p4, OTP As ULong
    Dim pt As Long
    
End Sub

Private Sub AppStart
    
    
    Serial1.Initialize(115200)
    
    Log("AppStart")
    

    If SSID.Length>0 And SSIDPW.Length>0 Then
        Log("Connecting to ",SSID)
        For i=1 To 10
            Log(i)
            
            If WiFi.Connect2(SSID,SSIDPW) Then
                Log("Connected to ",SSID)
                Log("My ip: ", WiFi.LocalIp)
                Exit
            Else
                Log("Could not connect to WiFi. Please check SSID and PW...")
            End If
        Next
    Else
        Log("Please define SSID + SSID-PW...")
    End If
    
    
    GetOTP
    
End Sub

Sub GetOTP
    RunNative("GetTime", Null)
    Dim utshex16 As String = JoinStrings(Array As String("000000000",bc.StringFromBytes(uthex)))
        
    Dim s As String="Secret"
    bc.ArrayCopy2(s,0,hmackey,0,s.Length)
    hmackey_len=s.Length
    Dim pl() As Byte=bc.HexToBytes(utshex16)
    
    bc.ArrayCopy2(pl,0,hmacpayload,0,pl.Length)
    hmacpayload_len=pl.Length
    
    RunNative("GetHmacSHA1", Null)
        
    Dim Offs As UInt= Bit.And(hmacbytessha1(19),15)
    
    p1=Bit.ShiftLeft(Bit.And(hmacbytessha1(Offs+0),127),24)
    p2=Bit.ShiftLeft(Bit.And(hmacbytessha1(Offs+1),255),16)
    p3=Bit.ShiftLeft(Bit.And(hmacbytessha1(Offs+2),255),8)
    p4=Bit.And(hmacbytessha1(Offs+3),255)
    
    RunNative("DoOr", Null) 'Did not manage it in B4R ;-)

    Dim d As ULong=Power(10,6)
    OTP = pt Mod d

    Log("OTP: ",NumberFormat(OTP,6,0))

End Sub

#if c

void DoOr (B4R::Object* o) {

    long pt;
    
    pt=b4r_main::_p1 | b4r_main::_p2;
    pt=pt | b4r_main::_p3;
    pt=pt | b4r_main::_p4;
    
    b4r_main::_pt = pt;

}


#End If



#if c

#include "mbedtls/md.h"

void GetHmacSHA1 (B4R::Object* o) {
 
  mbedtls_md_context_t ctx;
  mbedtls_md_type_t md_type = MBEDTLS_MD_SHA1;

  mbedtls_md_init(&ctx);
  mbedtls_md_setup(&ctx, mbedtls_md_info_from_type(md_type), 1);
  mbedtls_md_hmac_starts(&ctx, (unsigned char *)b4r_main::_hmackey->data, b4r_main::_hmackey_len);
  mbedtls_md_hmac_update(&ctx, (unsigned char *)b4r_main::_hmacpayload->data, b4r_main::_hmacpayload_len);
  mbedtls_md_hmac_finish(&ctx, (unsigned char *)b4r_main::_hmacbytessha1->data);
  mbedtls_md_free(&ctx);
}
#End If


#if c

#include "time.h"
#include <inttypes.h>
#include <math.h>
void GetTime (B4R::Object* o) {

    const char* ntpServer = "pool.ntp.org";
    const long  gmtOffset_sec = 3600;
    const int   daylightOffset_sec = 3600;

    configTime(gmtOffset_sec, daylightOffset_sec, ntpServer);

    struct tm timeinfo;
      if(!getLocalTime(&timeinfo)){
        Serial.println("Failed to obtain time");
        
      }
    else
    {
          Serial.println(&timeinfo, "%A, %B %d %Y %H:%M:%S");
    }
    
    
    struct timeval tv_now;
    gettimeofday(&tv_now, NULL);

    int64_t time_ms = (int64_t)tv_now.tv_sec * 1000LL + (int64_t)tv_now.tv_usec / 1000LL;
    int t1=floor(time_ms / 1000/ 30);
    
    b4r_main::_unixtimestamp=t1;
    String tuthex = String(t1, HEX);
    
    memcpy(b4r_main::_uthex->data,&tuthex, tuthex.length());
    
}

#End If