Overview
This lecture discusses the vulnerabilities of the RC4 encryption algorithm in HTTPS and WPA-TKIP, demonstrating practical attacks that allow decryption of sensitive information like web cookies and network packets.
Introduction to RC4 and HTTPS
- HTTPS is used to secure web communications, often indicated by a lock icon in the browser.
- RC4 was once widely used for HTTPS encryption but is now largely deprecated.
- The RC4 NOMORE attack exposes weaknesses in RC4, enabling attackers to decrypt web cookies.
RC4 NOMORE Attack Details
- The attack can decrypt web cookies, allowing attackers to impersonate victims on websites.
- The process involves injecting malicious JavaScript, capturing encrypted requests, and testing likely cookie values.
- The attack is practical, requiring as little as 52 hours to recover a cookie from real devices.
Demonstration and Impact
- Proof-of-concept attack was performed against a fictitious website using Internet Explorer.
- Roughly 92 million encryptions of a cookie are needed for a 94% success rate, achievable in about 75 hours.
- If lucky, less traffic is needed; decryption of cookies can happen in as little as 52 hours.
Broader Implications
- The attack can decrypt any repeatedly encrypted data, not just cookies.
- Similar attacks can be carried out against WPA-TKIP wireless networks, with network access gained in about an hour.
Comparison to Previous Attacks
- Previous attacks required much more time and could only be simulated, not performed on real devices.
- RC4 NOMORE reduces attack time from thousands to dozens of hours and increases request generation efficiency.
Underlying Weaknesses in RC4
- The attack exploits statistical biases in the RC4 keystream: Fluhrer-McGrew biases (biased consecutive bytes) and Mantin's ABSAB biases (repeated pairs).
- These biases allow recovery of repeated plaintext like cookies.
Countermeasures and Recommendations
- The only robust defense is to stop using RC4 entirely.
- Slowing down request generation can make attacks more expensive but not prevent them.
Key Terms & Definitions
- HTTPS — Protocol securing data between browsers and websites.
- RC4 — Stream cipher formerly used in TLS/HTTPS and Wi-Fi (WPA-TKIP).
- Web Cookie — Data used by websites to identify/authenticate users.
- Statistical Bias — Predictable patterns in encrypted data that attackers exploit.
- Fluhrer-McGrew Biases — Biases in consecutive RC4 keystream bytes.
- Mantin's ABSAB Biases — Biases where pairs of consecutive keystream bytes repeat.
Action Items / Next Steps
- Stop using RC4 in all security protocols.
- Review the linked research paper and demonstration slides for deeper understanding.
- Analyze detailed graphs and datasets provided in the lecture resources.