Hardcoded Keys & Static IVs

← Insufficient Cryptography

hardcoded_keys_ivs   EASY

Description

Symmetric key and IV baked into the binary; IV reused across messages.

How it works

The AES key and IV are hardcoded in the app and the same IV is reused for every message. Extracting the key with standard reverse-engineering tools (jadx/strings on Android, class-dump/nm/strings on iOS) decrypts all traffic forever, and IV reuse in CBC makes identical plaintexts produce identical ciphertexts, so encrypting the same input twice yields the same hex output.

How to exercise it. DVMA is the harness - open this module from the home index and tap the demo action. The screen ships the malicious input and simulates the attacker (e.g. the companion app, crafted intent, or scanned payload) in-process, and the evidence panel prints the proof. The Tools (optional) and Attack inputs below are only needed to reproduce the exploit end-to-end on a real device.

Exploit steps

1. Set up. Build DVMA with a flavor that enables the Insufficient Cryptography category (e.g. --dart-define-from-file=config/flavors/dev.json) and run on an emulator/simulator you control. The demo needs no external tooling; for the optional on-device reproduction the relevant tools are: strings, frida, r2, MobSF, JEB · Android: jadx, apktool, apkleaks · iOS: ipsw, class-dump, Hopper, otool.
2. Locate the target. From the home index, open Hardcoded Keys & Static IVs (hardcoded_keys_ivs). The How it works section above describes this module’s specific weakness; the screen states the intended-secure behavior and exposes the vulnerable action.
3. Exploit. Capture the algorithm/key/IV the module uses (the evidence panel prints it), then reproduce the weakness offline - e.g. recompute the digest, brute the short key, or decrypt a captured blob - to show the protection is ineffective.
4. Observe the evidence. Trigger the vulnerable action and read the evidence panel - it prints the concrete proof (leaked value, accepted replay, executed payload, or unauthorized result).
5. Contrast with the secure path. Run the module’s secure/hardened action (where provided) and confirm the same attack is rejected - this is what a correct implementation should do.
6. Map it back. Cross-reference the MASTG v2 test(s) MASTG-TEST-0212, MASTG-TEST-0214, MASTG-TEST-0309, MASTG-TEST-0310 for the canonical procedure and remediation.

Tools (optional)

• strings
• frida
• r2
• MobSF
• JEB

Android

• jadx
• apktool
• apkleaks

iOS

• ipsw
• class-dump
• Hopper
• otool