Communications of the ACM
Neuroscience Meets Cryptography: Crypto Primitives Secure Against Rubber Hose Attacks
Credit: Impulse
Cryptographic systems often rely on the secrecy of cryptographic keys given to users. Many schemes, however, cannot resist coercion attacks where the user is forcibly asked by an attacker to reveal the key. These attacks, known as rubber hose cryptanalysis, are often the easiest way to defeat cryptography. We present a defense against coercion attacks using the concept of implicit learning from cognitive psychology. Implicit learning refers to learning of patterns without any conscious knowledge of the learned pattern. We use a carefully crafted computer game to allow a user to implicitly learn a secret password without them having any explicit or conscious knowledge of the trained password. While the trained secret can be used for authentication, participants cannot be coerced into revealing it since they have no conscious knowledge of it. We performed a number of user studies using Amazon's Mechanical Turk to verify that participants can successfully re-authenticate over time and that they are unable to reconstruct or even robustly recognize the trained secret.
1. Introduction
Consider the following scenario: a high security facility employs a sophisticated authentication system to check that only persons who know a secret key, possess a hardware token, and have an authorized biometric can enter. Guards ensure that only people who successfully authenticate can enter the facility. Suppose a clever attacker captures an authenticated user. The attacker can steal the user's hardware token, fake the user's biometrics, and coerce the victim by threatening them with a weapon such as a rubber hose into revealing his or her secret key. At this point, the attacker can impersonate the victim and defeat the expensive authentication system deployed at the facility.
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