International Association for Cryptologic Research

International Association
for Cryptologic Research


Ersin Uzun


HAPADEP: Human Asisted Pure Audio Device Pairing
The number and diversity of electronic gadgets has been steadily increasing and they are becoming indispensable to more and more professionals and non-professionals alike. At the same time, there has been fairly little progress in secure pairing of such devices. The pairing challenge revolves around establishing on-the-fly secure communication without any trusted (on- or off-line) third parties between devices that have no prior association. The main security issue is the danger of so-called Man-in-the-Middle (MiTM) attacks, whereby an adversary impersonates one of the devices by inserting itself into the pairing protocol. One basic approach to countering these MiTM attacks is to involve the user in the pairing process. Therein lies the usability challenge since it is natural to minimize user burden. Previous research yielded some interesting secure pairing techniques, some of which ask too much of the human user, while others assume availability of specialized equipment (e.g., wires, photo or video cameras) on devices. Furthermore, all prior methods assumed the existence of a common digital (humanimperceptible) communication medium, such as Infrared, 802.11 or Bluetooth. In this paper we introduce a very simple technique called HAPADEP (Human-Assisted Pure Audio Device Pairing). It places very little burden on the human user and requires no common means of electronic communication. Instead, HAPADEP uses the audio channel to exchange both data and verification information among devices. It makes secure pairing possible even if devices are equipped only with a microphone and a speaker. Despite its simplicity, a number of interesting issues arise in the design of HAPADEP. We discuss design and implementation highlights as well as usability features and limitations.
BEDA: Button-Enabled Device Pairing
Secure initial pairing of electronic gadgets is a challenging problem, especially considering lack of any common security infrastructure. The main security issue is the threat of so-called Man-in-the-Middle (MiTM) attacks, whereby an attacker inserts itself into the pairing protocol by impersonating one of the legitimate parties. A number of interesting techniques have been proposed, all of which involve the user in the pairing process. However, they are inapplicable to many common scenarios where devices to-be-paired do not possess required interfaces, such as displays, speakers, cameras or microphones. In this paper, we introduce BEDA (Button-Enabled Device Association), a protocol suite for secure pairing devices with minimal user interfaces. The most common and minimal interface available on wide variety of devices is a single button. BEDA protocols can accommodate pairing scenarios where one (or even both) devices only have a single button as their "user interface". Our usability study demonstrates that BEDA protocols involve very little human burden and are quite suitable for ordinary users.
Loud and Clear: Human-Verifiable Authentication Based on Audio
Secure pairing of electronic devices that lack any previous association is a challenging problem which has been considered in many contexts and in various flavors. In this paper, we investigate an alternative and complementary approach--the use of the audio channel for human-assisted authentication of previously un-associated devices. We develop and evaluate a system we call Loud-and-Clear (L&C) which places very little demand on the human user. L&C involves the use of a text-to-speech (TTS) engine for vocalizing a robust-sounding and syntactically-correct (English-like) sentence derived from the hash of a device's public key. By coupling vocalization on one device with the display of the same information on another device, we demonstrate that L&C is suitable for secure device pairing (e.g., key exchange) and similar tasks. We also describe several common use cases, provide some performance data for our prototype implementation and discuss the security properties of L&C.