In the secure group communication, data is transmitted in such a way that only the group members are able to receive the messages. The main problem in the solution using symmetric key is heavy re-keying cost. To reduce re-keying cost tree based architecture is used. But it requires extra overhead to balance the keytree in order to achieve logarithmic re-keying cost. The main challenging issue i...

Many emerging group oriented and collaborative applications such as audio/video conferences use the peer-to-peer paradigm. Confidentiality is an often demanded feature for such applications, e.g. in business meetings, to provide group privacy. To assure confidentiality in a meeting the partners have to agree upon a common secret key for encrypting their communication. This requires efficient di...

In this paper we present adaptive key recovery attacks on NTRU-based somewhat homomorphic encryption schemes. Among such schemes, we study the proposal by Bos et al [BLLN13] in 2013. Given access to a decryption oracle, the attack allows us to compute the private key for all parameter choices. Such attacks show that one must be very careful about the use of homomorphic encryption in practice. T...

Protocols for group key exchange are cryptographic algorithms that describe how a group of parties communicating over a public network can come up with a common secret key. Due to their critical role in building secure multicast channels, a number of group key exchange protocols have been proposed over the years for a variety of settings. In this work, we present a new protocol for password-aut...

One way to use Diffie-Hellman’s 1976 secret key exchange protocol is to create a key to be used in later rounds for symmetric encryption. This requires multiple rounds of communication. Rivest, Shamir, and Adleman in 1978 developed the one round communication scheme discussed earlier. Namely, in order for Bob to receive messages Bob produces an integer N = pq where p and q are primes of equal l...

Protocols for authenticated key exchange allow parties within an insecure network to establish a common session key which can then be used to secure their future communication. In this paper we introduce a protocol for distributed key agreement over a noncommutative ring with a large number of noninvertible elements. This protocol uses polynomials with coefficients in the center of the ring. We...

Group key management presents a fundamental challenge in secure dynamic group communications. In this paper, we propose an efficient group authenticated key agreement protocol (EGAKA), which is designed to be fully distributed and fault-tolerant, provides efficient dynamic group membership management, mutual authentication among group members and is secure against both passive and active attack...

The aim of this paper is to propose an efficient and simpler Contributory Group Key Agreement protocol (CGKA) based on Elliptic Curve Diffie Hellman (ECDH). In this CGKA protocol, a member acts as a group controller (GC) and forms two-party groups with remaining group members and generates an ECDH-style shared key per each two-party group. It then combines these keys into a single group key and...

Certificateless public key encryption is an advanced version of identity-based and public key encryption techniques. It eliminates the inherent key escrow and other key management issues in both techniques, e.g., it does not need any public key infrastructure or digital certificates. This paper presents a survey of the certificateless public key encryption schemes that have been proposed to imp...

Contrary to conventional cryptographic wisdom, the NIST SP 800-56A standard ex-plicitly allows the use of a static key pair in more than one of the key establishment protocolsdescribed in the standard. In this paper, we give examples of key establishment protocols that are individually secure, but which are insecure when static key pairs are reused in two of the protocols.We also pr...