Golang : Generate QR codes for Google Authenticator App and fix "Cannot interpret QR code" error



Tags : golang qr-codes generate png google-authenticator two-factor-authentication

This is a supplement tutorial for the previous tutorial on how to generate QR codes with Golang and how to fix the error "Cannot interpret QR code"

To generate QR codes that is acceptable to Google Authenticator App. You need to follow the URI format specified in https://github.com/google/google-authenticator/wiki/Key-Uri-Format. Otherwise, the QR codes will not be interpreted correctly by Google Authenticator. Your app users will see the following error when attempt to scan the QR code.

Cannot Interpret QR code

Below is a code example on how to generate the proper QR codes for Google Authenticator :

 package main

 import (
 "bytes"
 "code.google.com/p/rsc/qr"
 "crypto/rand"
 "encoding/base32"
 "fmt"
 "github.com/disintegration/imaging"
 "image"
 "os"
 "runtime"
 )

 func randStr(strSize int, randType string) string {

 var dictionary string

 if randType == "alphanum" {
 dictionary = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 }

 if randType == "alpha" {
 dictionary = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 }

 if randType == "number" {
 dictionary = "0123456789"
 }

 var bytes = make([]byte, strSize)
 rand.Read(bytes)
 for k, v := range bytes {
 bytes[k] = dictionary[v%byte(len(dictionary))]
 }
 return string(bytes)
 }

 func main() {

 // maximize CPU usage for maximum performance
 runtime.GOMAXPROCS(runtime.NumCPU())

 // generate a random string - preferably 6 or 8 characters
 randomStr := randStr(6, "alphanum")
 fmt.Println(randomStr)

 // For Google Authenticator purpose
 // for more details see
 // https://github.com/google/google-authenticator/wiki/Key-Uri-Format
 secret := base32.StdEncoding.EncodeToString([]byte(randomStr))

 // authentication link. Remember to replace SocketLoop with yours.
 // for more details see
 // https://github.com/google/google-authenticator/wiki/Key-Uri-Format
 authLink := "otpauth://totp/SocketLoop?secret=" + secret + "&issuer=SocketLoop"

 // Encode authLink to QR codes
 // qr.H = 65% redundant level
 // see https://godoc.org/code.google.com/p/rsc/qr#Level

 code, err := qr.Encode(authLink, qr.H)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 imgByte := code.PNG()

 // convert byte to image for saving to file
 img, _, _ := image.Decode(bytes.NewReader(imgByte))

 err = imaging.Save(img, "./QRImgGA.png")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // everything ok
 fmt.Println("QR code generated and saved to QRimgGA.png")

 }

Output ( tested with Google Authenticator app ) :

QRimgGA.png

Hope this tutorial can be helpful to you!

References :

http://blog.gopheracademy.com/advent-2013/day-21-two-factor-auth/

https://github.com/google/google-authenticator/wiki/Key-Uri-Format

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  See also : Golang : How to generate QR codes?



Tags : golang qr-codes generate png google-authenticator two-factor-authentication

By Adam Ng

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