Secure Group Communication in Ad-Hoc Networks using Tree Parity Machines

Abstract. A fundamental building block of secure group communication is the establishment of a common group key. This can be divided into key agreement and key distribution. Common group key agreement protocols are based on the Diffie-Hellman (DH) key exchange and extend it to groups. Group key distribution protocols are centralized approaches which make use of one or more special key servers. In contrast to these approaches, we present a protocol which makes use of the Tree Parity Machine key exchange between multiple parties. It does not need a centralized server and therefore is especially suitable for ad-hoc networks of any kind.

Tribenzotriquinacene receptors for C60 fullerene rotors: towards C3 symmetrical chiral stators for unidirectionally operating nanoratchets

The synthesis of a stereochemically pure concave tribenzotriquinacene receptor (7) for C-60 fullerene, possessing C-3 point group symmetry, by threefold condensation of C-2-symmetric 1,2-diketone synthons (5) and a hexaaminotribenzotriquinacene core (6) is described. The chiral diketone was synthesized in a five-step reaction sequence starting from C-2h-symmetric 2,6-di-tert-butylanthracene. The highly diastereo-discriminating Diels-Alder reaction of 2,6-di-tertbutylanthracene with fumaric acid di(-)menthyl ester, catalyzed by aluminium chloride, is the relevant stereochemistry introducing step. The structure of the fullerene receptor was verified by H-1 and C-13 NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction. VCD and ECD spectra were recorded, which were corroborated by ab initio DFT calculations, establishing the chiral nature of 7 with about 99.7% ee, based on the ee (99.9%) of the chiral synthon (1). The absolute configuration of 7 could thus be established as all-S [(2S,7S,16S,21S,30S,35S)-(7)]. Spectroscopic titration experiments reveal that the host forms 1: 1 complexes with either pure fullerene (C-60) or fullerene derivatives, such as rotor 1'-(4-nitrophenyl)-3'-(4-N,N-dimethylaminophenyl)-pyrazolino[4',5':1,2][60]fullerene (R). The complex stability constants of the complexes dissolved in CHCl3/CS2 (1:1 vol.%) are K([C-60 subset of 7])= 319(+/- 156) M-1 and K([R subset of 7])= 110(+/- 50) M-1. With molecular dynamics simulations using a first-principles parameterized force field the asymmetry of the rotational potential for [R subset of 7] was shown, demonstrating the potential suitability of receptor 7 to act as a stator in a unidirectionally operating nanoratchet