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StarHub Password Encryption Technique

Reverse Engineering Stage

Using [GitHub] skylot/jadx to decompile My StarHub app, I started digging through the source code.

There are 3 parts to this documentation

  1. How StarHub encrypts/decrypt the plaintext password and hub id email to the local SQLite DB (Android)

  2. How StarHub encrypts/decrypt the plaintext password for HTTPS request payload

  3. Implementing the algorithm in Python

Encryption/Decryption from SQLite DB (Android)

import java.security.Key;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

Encryption to SQLite

public static String encrypt(String str) throws Exception {
    byte[] bytes = "2eobgrwapapifsxa".getBytes();
    AlgorithmParameterSpec ivParameterSpec = new IvParameterSpec("jsfkew4plc20mnds".getBytes());
    Key secretKeySpec = new SecretKeySpec(bytes, "AES");
    Cipher instance = Cipher.getInstance("AES/CBC/PKCS5Padding");
    instance.init(1, secretKeySpec, ivParameterSpec);   // 1: ENCRYPT_MODE
    return Base64.encodeToString(instance.doFinal(str.getBytes()), 0);
}

Decryption from SQLite

public static String decrypt(String str) throws Exception {
    byte[] bytes = "2eobgrwapapifsxa".getBytes();
    AlgorithmParameterSpec ivParameterSpec = new IvParameterSpec("jsfkew4plc20mnds".getBytes());
    Key secretKeySpec = new SecretKeySpec(bytes, "AES");
    Cipher instance = Cipher.getInstance("AES/CBC/PKCS5Padding");
    instance.init(2, secretKeySpec, ivParameterSpec);   // 2: DECRYPT_MODE
    return new String(instance.doFinal(Base64.decode(str, 0)));
}

Encryption/Decryption for HTTPS Request Payload

This part involves 2 Strings, the password and the salt.

The password and salt was retrieved from a class (class name obfuscated) under the package com.starhub.csselfhelp.utils.

PRODUCTION(
 "https://fapi.starhub.com/MyStarhub",
 "http://fapi.starhub.com/MyStarhub",
 "https://login.starhubgee.com.sg/sso/api/common",
 "FZH9f/TWMhNR2vLC7M0Tuhy/8jG1it8H",
 "1d2286041ee068cb1561f2838e0e71fa",
 "U09wQs6svgbl",        // password
 "a54792ef11d53c68",    // salt
 "https://starhubvocsurveys.com/backend/web/survey?feed_id=",
 "https://login.starhubgee.com.sg/msso/bapp/api/ssoredirect?src_siteid=mystarhub&src_token=%1$s&src_session_id=%2$s&tgt_siteid=jprotect&cb=https://juniorprotect.starhub.com/user/index.html"
)

Encryption Algorithm

The encryption of the password is based on SpringFramework's Encryptors. This information is gathered from the decompiled source code.

import org.springframework.security.crypto.encrypt.Encryptors;

public static String encrypt(String str) {
    String password = "U09wQs6svgbl";
    String salt = "a54792ef11d53c68";
    return Encryptors.text(password, salt).encrypt(str);
}

From what I understand, the encryption library (default setting) uses:

  • 256 bit AES encryption and derives the secret key using PKCS #5's PBKDF2.
  • The provided salt is expected to be hex-encoded and at least 8 bytes in length
  • Also applies a random 16 byte initialization vector (IV) to ensure uniqueness

SpringFramework Encryptor Documentation (4.2.5)

Format of Input Password

In one of the Android Activity, I found this line of code (obfuscated)

private MSSOLoginResponse a() {
    this.b = com.starhub.csselfhelp.chat.utils.a.c(this.b + "_" + System.currentTimeMillis());
    return com.starhub.csselfhelp.network.c.b(MyStarHubApplication.d().b("KEY_MSSO_LOGIN_URL", ""), String.format("{\"user_id\":\"%1$s\",\"user_password\":\"%2$s\",\"site_id\":\"%3$s\"}", new Object[] {
  this.a, this.b, "mystarhub"
 }), this.f.b);
}

this.b represents the plaintext password. What StarHub does is that it appends _ plus current time in milliseconds behind the plaintext password.

Input: YOURPASSWORD_1529598919501

Output: 1a5ebfa6e2445515451af1f7fa2b45ec8385514c660f611ec1ee05478d0083b96848e2f064f51100242b9242e956dff1

Implementing in Python

TODO: Test sample implementation in Python

Someone has already done the implementation in Python thanks to this article: http://www.tmarthal.com/2016/07/using-pycrypto-with-spring-cryptospring.html archive.org link here

The fork of the GitHub Gist is available here: https://gist.github.com/Vantablack/21ec8f66974c5b22627d120671a71d9c