google authentication base on time

README.md

google authentication base on time in Racket Programming Language

How to use

following these steps below:

1. install package racket-base32:

raco pkg install https://github.com/sackpost/racket-base32.git

2. test it:

raco test google-auth.rkt

google-auth.rkt

#lang racket/base

(require base32
         file/sha1
         web-server/stuffers/hmac-sha1
         racket/contract)

(define/contract (get-code key)
  (-> bytes? integer?)
  (let* ([key (base32-decode key)]
         [code (hex-string->bytes
                (string-append "0"
                               (number->string (round (/ (current-seconds) 30)) 16)))]
         [fdb (bytes-append
               (apply bytes-append
                      (for/list ([_ (- 8 (bytes-length code))])
                        (bytes 0)))
               code)]
         [hmac (HMAC-SHA1 key fdb)]
         [o (bitwise-and (bytes-ref hmac 19) 15)]
         [h (subbytes hmac o (+ o 4))]
         [q1 (arithmetic-shift
              (+ (arithmetic-shift (bytes-ref h 0) 8)
                 (bytes-ref h 1))
              16)]
         [q2 (+ (arithmetic-shift (bytes-ref h 2) 8)
                (bytes-ref h 3))]
         [qq (+ q1 q2)]
         [mid (bitwise-and qq #x7fffffff)])
    (remainder mid 1000000)))

(module+ test
  (displayln (get-code #"VBKVUBKHV4EB2IEB")))