# Firmware Encryption Attacks: Mitigating CBC Malleability
> Learn how malleability attacks target AES-CBC in encrypted firmware updates and why authenticated encryption (AEAD) is essential for IoT security.

Tags: firmware-security, aes-cbc-attack, arm-microcontroller, embedded-security, cybersecurity, code-injection, aead
## Practical Evaluation of Code Injection in Encrypted Firmware
* Critical analysis of malleability attacks on AES-CBC in ARM Microcontrollers.
* Based on research by O. Guillen, D. Schmidt, & G. Sigl.

## The False Sense of Security
* Symmetric encryption (AES-CBC) without integrity checks is vulnerable.
* Encryption provides confidentiality, but not necessarily security against manipulation.

## Mechanism: CBC Malleability
* Modifying a bit in Ciphertext Block N-1 produces a predictable bit flip in Plaintext Block N during decryption.

## Targeting the ARM Exception Vector Table (EVT)
* Attackers use 'Known Plaintext' found in the ARM Cortex-M EVT (at 0x00000000).
* Reserved vectors initialized to zero provide a canvas for injection.

## The Copy-and-Paste Attack Strategy
* Replicating ciphertext blocks creates a chain of writable memory sections.
* Expands small spaces into larger areas for malicious payloads.

## Technical Implementation: Jump & Trigger
* **Jump Technique:** Code must jump over 'garbage' decryption blocks created by the attack.
* **Execution:** Attackers bit-flip IRQ vector addresses to point to injected code, triggered by physical interactions like button presses.

## Proof of Concept: Infineon XMC4500
* Targeted an ARM Cortex-M4 chip.
* Injected a SPI transmitter payload to extraction firmware and secret keys via GPIO pins.

## Mitigation: Authenticated Encryption
* Use AEAD modes like **AES-GCM** or **AES-CCM**.
* Authentication tags ensure that any modification to ciphertext causes validation failure before execution.

## Key Takeaways
* Encryption does not guarantee integrity.
* Secrets can be extracted without a key via code injection.
* Always use Authenticated Encryption (AEAD) for firmware updates.
---
This presentation was created with [Bobr AI](https://bobr.ai) — an AI presentation generator.