Continuous authentication has been proposed as a possible approach for passive and seamless user authentication, using sensor data comprising biometric, behavioral, and context-oriented characteristics. Since these are personal data being transmitted and are outside the control of the user, this approach causes privacy issues. Continuous authentication has security challenges concerning poor matching rates and susceptibility of replay attacks. The security issues are mainly poor matching rates and the problems of replay attacks. In this survey, we present an overview of continuous authentication and comprehensively discusses its different modes, and issues that these modes have related to security, privacy, and usability. A comparison of privacy-preserving approaches dealing with the privacy issues is provided, and lastly recommendations for secure, privacy-preserving, and user-friendly continuous authentication.

Cryptographic schemes that provide establishment of secret keys among a number of participants are generally known as conference key establishment schemes and key broadcasting schemes. In any case, such protocols provide secure establishment of group-oriented cryptographic keys, but with the costs of multiple transmissions of key establishment messages and in some cases multiple secret user keys. In this paper, we present a simple and straightforward efficient non-interactive group-oriented key establishment scheme that provides off-line computation of secret group keys, without computations and transmissions of key establishment messages

In this paper, we present three related and efficient cryptographic schemes for secure communication for hierarchically composed user groups. In such a group, each user is associated with a hierarchical level, so that the group members are divided into two or more hierarchical security classes. Most existing hierarchical cryptographic schemes provide hierarchical deduction of hierarchically arranged predefined keys. In contrast, the first scheme provides secure establishment of hierarchically ordered session keys. Since it prohibits long-term key deduction for underlying (and overlying) classes, such keys do not need to be updated session-wise. An essential security property is that the users can only obtain hierarchical session keys for their own and underlying levels, while it is prevented that a user can obtain hierarchical session keys of overlying levels.This scheme is extended to a hierarchical public key cryptosystem based on the ElGamal cryptosystem, and furthermore to an ElGamal-based threshold decryption scheme. Due to the threshold security requirement, at least t arbitrary group members are required to carry out decryption. The threshold scheme requires only one round of broadcasting in the decryption phase, and is thus well-suitable for wireless networks.

No abstract

No abstract