Verify OTP Without SMS Permission In Android Using Kotlin

Introduction

Verification Message Format

1. A message should have a maximum of 140 bytes length.
2. Should start with “<#>”.
3. Followed by OTP - One Time Pass (code/word).
4. 11 character length hash for the app (it is generated by our app).

Coding Part

1. Open Android Studio and select "Create new project".
2. Name the project as your wish and tick the Kotlin Support checkbox.
3. Then Select your Activity type (For example, Navigation Drawer Activity, Empty Activity, etc.).
   
   
   
   
   
4. Then, click the “Finish” button to create a new project in Android Studio.

1. Then add the following lines in app level build.gradle file to apply Google services to your project.
   
   1. dependencies {
   2. …
   3. implementation 'com.google.android.gms:play-services-base:11.6.0'
   4. implementation 'com.google.android.gms:play-services-auth-api-phone:11.6.0'
   5. …
   6. }

2. Then click “Sync Now” to setup your project.
3. Now the project is ready and no need to add any permissions in Manifest.

• Create a user interface to display your OTP read through the API. Open or create “activity_main.xml” and paste the following code snippet.
  
  1. <?xml version="1.0" encoding="utf-8"?>
  2. <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3. xmlns:app="http://schemas.android.com/apk/res-auto"
  4. xmlns:tools="http://schemas.android.com/tools"
  5. android:layout_width="match_parent"
  6. android:layout_height="match_parent"
  7. tools:context="com.androidmad.smsretrieverapisample.MainActivity">
  9. <EditText
  10. android:id="@+id/editText"
  11. android:layout_width="match_parent"
  12. android:layout_height="wrap_content"
  13. android:layout_marginLeft="20dp"
  14. android:layout_marginRight="20dp"
  15. app:layout_constraintBottom_toBottomOf="parent"
  16. app:layout_constraintLeft_toLeftOf="parent"
  17. app:layout_constraintRight_toRightOf="parent"
  18. app:layout_constraintTop_toTopOf="parent" />
  20. <Button
  21. android:onClick="onBtnResendClick"
  22. android:id="@+id/btn_restart"
  23. android:text="Resend"
  24. android:layout_width="0dp"
  25. android:layout_height="wrap_content"
  26. android:layout_marginLeft="20dp"
  27. android:layout_marginRight="20dp"
  28. app:layout_constraintBottom_toBottomOf="parent"
  29. app:layout_constraintEnd_toEndOf="parent"
  30. app:layout_constraintHorizontal_bias="0.0"
  31. app:layout_constraintLeft_toLeftOf="parent"
  32. app:layout_constraintRight_toRightOf="parent"
  33. app:layout_constraintStart_toStartOf="parent"
  34. app:layout_constraintTop_toTopOf="@id/editText"
  35. app:layout_constraintVertical_bias="0.247" />
  37. </android.support.constraint.ConstraintLayout>

• We need to create a helper class to provide the hash value for our app to construct the verification message. Create a Kotlin class file named as “AppSignatureHelper.kt” and paste the following code snippet which is helpful to create an 11 character length hash for our application.
  
  1. package com.androidmad.smsretrieverapisample
  3. import android.annotation.SuppressLint
  4. import android.content.Context
  5. import android.content.ContextWrapper
  6. import android.content.pm.PackageManager
  7. import android.os.Build
  8. import android.support.annotation.RequiresApi
  9. import android.util.Base64
  10. import android.util.Log
  11. import java.nio.charset.StandardCharsets
  12. import java.security.MessageDigest
  13. import java.security.NoSuchAlgorithmException
  14. import java.util.*
  16. class AppSignatureHelper(context: Context) : ContextWrapper(context) {
  18. /**
  19. * Get all the app signatures for the current package
  20. *
  21. * @return
  22. */
  23. // Get all package signatures for the current package
  24. // For each signature create a compatible hash
  25. val appSignatures: ArrayList<String>
  26. @SuppressLint("PackageManagerGetSignatures")
  27. @RequiresApi(api = Build.VERSION_CODES.KITKAT)
  28. get() {
  29. val appCodes = ArrayList<String>()
  31. try {
  32. val packageName = packageName
  33. val packageManager = packageManager
  34. val signatures = packageManager.getPackageInfo(packageName,
  35. PackageManager.GET_SIGNATURES).signatures
  36. signatures
  37. .mapNotNull { hash(packageName, it.toCharsString()) }
  38. .mapTo(appCodes) { String.format("%s", it) }
  39. } catch (e: PackageManager.NameNotFoundException) {
  40. Log.v(TAG, "Unable to find package to obtain hash.", e)
  41. }
  43. return appCodes
  44. }
  46. companion object {
  47. val TAG = AppSignatureHelper::class.java.simpleName!!
  48. private val HASH_TYPE = "SHA-256"
  49. private val NUM_HASHED_BYTES = 9
  50. private val NUM_BASE64_CHAR = 11
  52. @RequiresApi(api = Build.VERSION_CODES.KITKAT)
  53. private fun hash(packageName: String, signature: String): String? {
  54. val appInfo = packageName + " " + signature
  55. try {
  56. val messageDigest = MessageDigest.getInstance(HASH_TYPE)
  57. messageDigest.update(appInfo.toByteArray(StandardCharsets.UTF_8))
  58. var hashSignature = messageDigest.digest()
  60. // truncated into NUM_HASHED_BYTES
  61. hashSignature = Arrays.copyOfRange(hashSignature, 0, NUM_HASHED_BYTES)
  62. // encode into Base64
  63. var base64Hash = Base64.encodeToString(hashSignature, Base64.NO_PADDING or Base64.NO_WRAP)
  64. base64Hash = base64Hash.substring(0, NUM_BASE64_CHAR)
  66. Log.v(TAG + "sms_sample_test", String.format("pkg: %s -- hash: %s", packageName, base64Hash))
  67. return base64Hash
  68. } catch (e: NoSuchAlgorithmException) {
  69. Log.v(TAG + "sms_sample_test", "hash:NoSuchAlgorithm", e)
  70. }
  72. return null
  73. }
  74. }
  75. }