RSA Without OAEP Padding

← Insufficient Cryptography

rsa_no_oaep_padding   MEDIUM

Description

A payload is RSA-encrypted with legacy PKCS#1 v1.5 padding instead of OAEP, exposing it to Bleichenbacher-style chosen-ciphertext padding-oracle attacks; the secure path uses RSA-OAEP.

How it works

A payload is RSA-encrypted with legacy PKCS#1 v1.5 padding instead of OAEP. PKCS#1 v1.5 is malleable and its padding-validity behavior is a classic chosen-ciphertext (Bleichenbacher) oracle, letting an attacker who can submit modified ciphertexts recover the plaintext without the private key. The module encrypts the same payload both ways with a real RSA keypair and shows that v1.5 padding produces structurally weaker, oracle-exposed ciphertext, while the secure path uses RSA-OAEP, whose randomized, non-malleable padding closes the oracle.

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: frida, openssl.
2. Locate the target. From the home index, open RSA Without OAEP Padding (rsa_no_oaep_padding). 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.

Tools (optional)

• frida
• openssl