Seeing-Is-Believing: Using Camera Phones for Human- Verifiable Authentication Jonathan M. McCune Adrian Perrig Michael K. Reiter Carnegie Mellon University 2005報告人：張淯閎

Outline Related works Related works Authentication Authentication Barcode Recognition with Camera Phones Barcode Recognition with Camera Phones Seeing-Is-Believing Seeing-Is-Believing

Authentication Authentication between two co-located entities with no prior trust relationships. Authentication between two co-located entities with no prior trust relationships. Public key infrastructure relies on trusted certifiers. Public key infrastructure relies on trusted certifiers. Diffie-Hellman key Diffie-Hellman key Man-in-the-middle Man-in-the-middle Encrypted key exchange Encrypted key exchange

Barcode Recognition with Camera Phones SiB depends on a camera phone and can recognize 2D barcodes. SiB depends on a camera phone and can recognize 2D barcodes. 2D code used in mobile phones can be read from electronic screens and printed paper(Rohs and Gfeller). 2D code used in mobile phones can be read from electronic screens and printed paper(Rohs and Gfeller). Semacodes, which is a Data Matrix barcode standard(Woodside). Semacodes, which is a Data Matrix barcode standard(Woodside). HP Labs propose tagging electronics with barcode to be read by camera phones. HP Labs propose tagging electronics with barcode to be read by camera phones.

Seeing-Is-Believing A mobile phone’s integrated camera serves as a visual channel to provide identification of communicating devices. A mobile phone’s integrated camera serves as a visual channel to provide identification of communicating devices. User identifies that other device visually. User identifies that other device visually. With 2D barcodes With 2D barcodes

Pre-Authentication and the Visual channel SiB uses a visual channel instead of an invisible channel, thus adding a direct human factor. SiB uses a visual channel instead of an invisible channel, thus adding a direct human factor. Pre-authentication data is used in both communicating parties in any standard public-key over the wireless link.(Figure1.) Pre-authentication data is used in both communicating parties in any standard public-key over the wireless link.(Figure1.)

Figure1. Pre-authentication over the visual channel. Ka is A’s public key, which can be either long-term or ephemeral, depending the protocol.

Bidirectional Authentication Without a trusted authority Without a trusted authority Diffie-Hellman key exchange to establish a shared secret Diffie-Hellman key exchange to establish a shared secret Mutually authenticated one another’s public keys Mutually authenticated one another’s public keys

Unidirectional Authentication Figure2. Can a device of type X authenticate a device of type Y? We consider devices with cameras and displays(CD), cameras only(C), displays only(D), and neither(N).

SiB For Example

Security Analysis Assumption that an attacker is unable to perform an active attack on the visual channel. Assumption that an attacker is unable to perform an active attack on the visual channel. Unable to compromise the mobile device itself. Unable to compromise the mobile device itself. Cryptography Cryptography Selecting an Authentication Channel Selecting an Authentication Channel

Conclusion SiB is a system that uses barcodes and camera phones as a visual channel for human-verifiable authentication. SiB is a system that uses barcodes and camera phones as a visual channel for human-verifiable authentication. Visual channel provides demonstrative identification of communicating parties,that user assurance her device. Visual channel provides demonstrative identification of communicating parties,that user assurance her device. SiB characteristic SiB characteristic

Diffie-Hellman key exchange n, g public value n, g public value Both sides have his own value like X and Y (must a large number ). Both sides have his own value like X and Y (must a large number ). Count Secrete Key g xy Count Secrete Key g xy Alice Bob Count: (g y mod n) x = g xy mod n Count: (g x mod n) y = g xy mod n n, g, g x mod n g y mod n