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A Trusted Channel is a secure communication channel which is cryptographically bound to the state of the hardware and software configurations of the endpoints. In this paper, we describe secure and flexible mechanisms to establish and maintain Trusted Channels which do not have the deficiencies of previous proposals. We also present a concrete implementation proposal based on Transport Layer Security (TLS) protocol, and Trusted Computing technology. We use Subject Key Attestation Evidence extensions to X.509v3 certificates to convey configuration information during key agreement (TLS handshake). The resulting session key is kept within the Trusted Computing Base, and is updated in a pre-determined manner to reflect any detected change in the local configuration. This allows an endpoint to detect changes in the configuration of the peer endpoint while the Trusted Channel is in place, and to decide according to a local policy whether to maintain or tear down the Trusted Channel.

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Abstract. SMS-based One-Time Passwords (SMS OTP)were introduced to counter phishing and other attacks against Internet services such as online banking. Today, SMS OTPs are commonly used for authentication and authorization for many different applications. Recently, SMS OTPs have come under heavy attack, especially by smartphone Trojans. In this paper, we analyze the security architecture of SMS OTP systems and study attacks that pose a threat to Internet-based authentication and authorization services. We determined that the two foundations SMS OTP is built on, cellular networks and mobile handsets, were completely different at the time when SMS OTP was designed and introduced. Throughout this work, we show why SMS OTP systems cannot be considered secure anymore. Based on our findings, we propose mechanisms to secure SMS OTPs against common attacks and specifically against smartphone Trojans.

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