mobile-weak-crypto

Mobile Weak Cryptography

What Is Broken and Why

Mobile apps frequently implement cryptography incorrectly: using broken algorithms (DES, RC4), insecure modes (ECB), static/reused IVs, hardcoded keys embedded in source or resources, or non-cryptographic RNGs for key generation. Android's java.util.Random is not a CSPRNG. iOS's arc4random() is acceptable but older code uses rand(). ECB mode leaks plaintext patterns in ciphertext. Hardcoded keys are extractable via static analysis of the APK or IPA in seconds.

Key Signals

• Cipher.getInstance("AES/ECB/NoPadding") or Cipher.getInstance("DES/...") in Android code
• kCCAlgorithmDES, kCCAlgorithmRC4 in iOS CommonCrypto calls
• Hardcoded hex/base64 strings adjacent to crypto API calls
• new Random() or Math.random() used to generate keys or IVs
• arc4random() replaced by rand() or custom PRNG in security-critical iOS code
• Static byte arrays used as IV: byte[] iv = {0,0,0,0,...}
• SecretKeySpec initialized directly from a string literal: new SecretKeySpec("hardcoded".getBytes(), "AES")
• RSA without OAEP: Cipher.getInstance("RSA/ECB/PKCS1Padding")
• Key sizes below 128-bit (AES), 2048-bit (RSA), 256-bit (EC)

Methodology

1. Static analysis — Android: Decompile APK with jadx or apktool; search for Cipher.getInstance, SecretKeySpec, MessageDigest, SecureRandom, Random()
2. Static analysis — iOS: Extract IPA; search Swift/ObjC source or binary strings for CCCrypt, kCCAlgorithm, SecKey, hardcoded key strings
3. Identify algorithm strings — grep for "DES", "ECB", "RC4", "MD5", "SHA-1" in decompiled code
4. Locate hardcoded key material — search for 16/32-byte hex strings, base64-encoded strings near crypto calls
5. Check IV handling — look for static IV byte arrays or IVs derived from non-random sources
6. Check key storage — verify keys are in Android Keystore / iOS Secure Enclave, not in SharedPreferences or NSUserDefaults
7. Dynamic analysis — use Frida to hook Cipher.doFinal() / CCCrypt() and log key, IV, and plaintext at runtime
8. Verify RNG — check that SecureRandom (Android) and SecRandomCopyBytes (iOS) are used for all security-sensitive randomness