Key agreement protocols are frequently based on the Diffie-Hellman protocol but require authenticating the protocol messages in two ways. This can be made by a cross-authentication protocol. Such protocols, based on the assumption that a channel which can authenticate short strings is available (SAS-based), have been proposed by Vaudenay. In this paper, we survey existing protocols and we propose a new one. Our proposed protocol requires three moves and a single SAS to be authenticated in two ways. It is provably secure in the random oracle model. We can further achieve security with a generic construction (e.g. in the standard model) at the price of an extra move. We discuss applications such as secure peer-to-peer VoIP.

Abstract.Vaudenay recently proposed a message authentication protocol which is interactive and based on short authenticated strings (SAS). We study here SASbased non-interactive message authentication protocols (NIMAP). We start by the analysis of two popular non-interactive message authentication protocols. The first one is based on a collision-resistant hash function and was presented by Balfanz et al. The second protocol is based on a universal hash function family and was proposed by Gehrmann, Mitchell, and Nyberg. It uses much less authenticated bits but requires a stronger authenticated channel.We propose a protocol which can achieve the same security as the first protocol but using less authenticated bits, without any stronger communication model, and without requiring a hash function to be collision-resistant. Finally, we demonstrate the optimality of our protocol.

Abstract. New trends in consumer electronics have created a strong demand for fast, reliable and user-friendly key agreement protocols. However, many key agreement protocols are secure only against passive attacks. Therefore, message authentication is often unavoidable in order to achieve security against active adversaries. Pasini and Vaudenay were the first to propose a new compelling methodology for message authentication. Namely, their two-party protocol uses short authenticated strings (SAS) instead of pre-shared secrets or public-key infrastructure that are classical tools to achieve authenticity. In this article, we generalise this methodology for multi-party settings. We give a new group message authentication protocol that utilises only limited authenticated communication and show how to combine this protocol with classical key agreement procedures. More precisely, we describe how to transform any group key agreement protocol that is secure against passive attacks into a new protocol that is secure against active attacks.

Abstract-The techniques generally used to detect compromising emanations are based on a wide-band receiver tuned on a specific frequency or a spectral analyzer with a limited bandwidth. However, these methods may not be optimal since a significant amount of information is lost during the signal acquisition. In this paper, we propose a straightforward but efficient approach which acquires raw signal directly from the antenna and processes the entire captured electromagnetic spectrum thanks to the computation of short time Fourier transforms. We applied this approach to detect potential compromising electromagnetic emanations radiated by modern keyboard. Since keyboards are often used to transmit confidential data such as passwords, these emanations could remotely reveal sensitive information such as keystrokes. Thanks to this method, we detected four different kinds of compromising electromagnetic emanations generated by wired and wireless keyboards. These emissions lead to a full or a partial recovery of the keystrokes. We implemented these side-channel attacks and our best practical attack fully recovered 95% of the keystrokes of a PS/2 keyboard at a distance up to 20 meters, even through walls.