Efficient and Secure Multicast in WirelessMAN: A Cross-layer Design

Effectively adding security measures to a multicast service is an intriguing problem, especially when the service isdeployed in a wireless setting. Next generation IEEE 802.16standard WirelessMAN networks are a perfect example of this problem, and the latest draft specification of the standard includes a secure protocol solution called Multicast and Broadcast Rekeying Algorithm (MBRA). In this paper, we expose the security problems of MBRA, including non-scalability and omission of backward and forward secrecy, and propose new approaches, ELAPSE and ELAPSE+, to address these problems. In particular, ELAPSE+ makes use of membership and mobility information gathered in the application layer to augment the adaptive group management in the MAC layer. We analyze the security property of ELAPSE and ELAPSE+, and compare their performances with MBRA by simulating group rekeying scenarios

Multi-Stage Group Key Distribution and PAKEs: Securing Zoom Groups against Malicious Servers without New Security Elements

Video conferencing apps like Zoom have hundreds of millions of daily users, making them a high-value target for surveillance and subversion. While such apps claim to achieve some forms of end-to-end encryption, they usually assume an incorruptible server that is able to identify and authenticate all the parties in a meeting. Concretely this means that, e.g., even when using the “end-to-end encrypted” setting, malicious Zoom servers could eavesdrop or impersonate in arbitrary groups. In this work, we show how security against malicious servers can be improved by changing the way in which such protocols use passwords (known as passcodes in Zoom) and integrating a password-authenticated key exchange (PAKE) protocol. To formally prove that our approach achieves its goals, we formalize a class of cryptographic protocols suitable for this setting, and define a basic security notion for them, in which group security can be achieved assuming the server is trusted to correctly authorize the group members. We prove that Zoom indeed meets this notion. We then propose a stronger security notion that can provide security against malicious servers, and propose a transformation that can achieve this notion. We show how we can apply our transformation to Zoom to provably achieve stronger security against malicious servers, notably without introducing new security elements

Multi-Stage Group Key Distribution and PAKEs: Securing Zoom Groups against Malicious Servers without New Security Elements

Video conferencing apps like Zoom have hundreds of millions of daily users, making them a high-value target for surveillance and subversion. While such apps claim to achieve some forms of end-to-end encryption, they usually assume an incorruptible server that is able to identify and authenticate all the parties in a meeting. Concretely this means that, e.g., even when using the “end-to-end encrypted” setting, malicious Zoom servers could eavesdrop or impersonate in arbitrary groups. In this work, we show how security against malicious servers can be improved by changing the way in which such protocols use passwords (known as passcodes in Zoom) and integrating a password-authenticated key exchange (PAKE) protocol. To formally prove that our approach achieves its goals, we formalize a class of cryptographic protocols suitable for this setting, and define a basic security notion for them, in which group security can be achieved assuming the server is trusted to correctly authorize the group members. We prove that Zoom indeed meets this notion. We then propose a stronger security notion that can provide security against malicious servers, and propose a transformation that can achieve this notion. We show how we can apply our transformation to Zoom to provably achieve stronger security against malicious servers, notably without introducing new security elements