Pedro Adão

Soundness of formal encryption in the presence of key-cycles

Both the formal and the computational models of cryptography contain the notion of message equivalence or indistinguishability. An encryption scheme provides soundness for indistinguishability if, when mapping formal messages into the computational model, equivalent formal messages are mapped to indistinguishable computational distributions. Previous soundness results are limited in that they do not apply when key-cycles are present. We demonstrate that an encryption scheme provides soundness in the presence of key-cycles if it satisfies the recently-introduced notion of key-dependent message (KDM) security. We also show that soundness in the presence of key-cycles (and KDM security) neither implies nor is implied by security against chosen ciphertext attack (CCA-2). Therefore, soundness for key-cycles is possible using a new notion of computational security, not possible using previous such notions, and the relationship between the formal and computational models extends beyond chosen-ciphertext security.

Vanadium Diaminebis(phenolate) Complexes: Syntheses, Structures, and Reactivity in Sulfoxidation Catalysis

Vanadium diaminebis(phenolate) complexes of the general formulas [LVCl(THF)] (L = Me(2)NCH(2)CH(R)N(CH(2)-2-O-3,5-C(6)H(2)(t)Bu(2))(2), where R = H, Me) and [LV(O)X] [X = Cl; R = H (2), Me (3), O(i)Pr (4), (mu-O)V(O)L (5)] are described. All compounds display octahedral geometry and trans-O(Ph) coordination. For compounds 2, 3, and 5, only one isomer, presenting the V=O ligand trans to the tripodal nitrogen, was formed, while for 4, two isomers were observed by NMR in solution. The UV-vis and circular dichroism spectra of 2 and 3 display very intense charge-transfer transition bands from the phenolate donors to the vanadium, which are in agreement with the (51)V low-field shifts observed. All vanadium(V) complexes were tested as thioanisole sulfoxidation catalysts, revealing very high selectivity when H(2)O(2) was used as the oxidant. However, no enantioselectivity was observed even when enantiopure 3 was used as the catalyst precursor. (1)H and (51)V NMR studies were conducted for the reactions of 2 with aqueous solutions of H(2)O(2) in methanol-d(4) and in acetonitrile-d(3); 2 reacts with the solvents, leading to [LV(O)OMe], by replacement of Cl by MeO in methanol, and to a new vanadium aminebis(phenolate) complex, where the dimethylamine fragment of the original ligand L was replaced by CH(3)CN. In either case, (51)V NMR spectra suggest the formation of peroxovanadium species upon the addition of a H(2)O(2) solution. The subsequent addition of thioanisole to the methanol-d(4) solution leads to regeneration of the original complex.

Vanadium-salen and -salan complexes: Characterization and application in oxygen-transfer reactions

Salen complexes are a versatile and standard system in oxidation catalysis. Their reduced derivatives, called salan, share their versatility but are still widely unexplored. We report the synthesis of a group of new vanadium-salen and -salan complexes, their characterization and application in the oxidation of simple organic molecules with H2O2. The ligands are derived from pyridoxal and chiral diamines (1,2-diaminocyclohexane and 1,2-diphenylethylenediamine) and were easily obtained in high yields. The VIV complexes were prepared and characterized in the solid state (Fourier transform infrared, FTIR, and magnetic properties) and in solution by spectroscopic techniques: UV–vis, circular dichroism (CD), electron paramagnetic resonance (EPR), and 51V NMR, which provide information on the coordination geometry. Single crystals suitable for X-ray diffraction studies were obtained from solutions containing the VIV-pyr(S,S-chan) complex: [VVO{pyr(S,S-chen)}]2(μ-O)2·2(CH3)2NCHO, where the ligand is the “half” Schiff base formed by pyridoxal and 1S,2S-diaminocyclohexane. The dinuclear species shows a OVV(μ-O)2VVO unit with tridentate ligands and two μ-oxo bridges. The VIV complexes of the salan-type ligands oxidize in organic solvents to a VV species, and the process was studied by spectroscopic techniques. The complexes were tested as catalysts in the oxidation of styrene, cyclohexene, and cumene with H2O2 as oxidant. Overall, the V-salan complexes show higher activity than the parent V-salen complexes and are an alternative ligand system for oxidation catalysis.

Computational and information-theoretic soundness and completeness of formal encryption

We consider expansions of the Abadi-Rogaway logic of indistinguishability of formal cryptographic expressions. We expand the logic in order to cover cases when partial information of the encrypted plaintext is revealed. We consider not only computational, but also purely probabilistic, information-theoretic interpretations. We present a general, systematic treatment of the expansions of the logic for symmetric encryption. We establish general soundness and completeness theorems for the interpretations. We also present applications to specific settings not covered in earlier works: a purely probabilistic one based on one-time pad, and computational settings of the so-called type-2 (which-key revealing) and type-3 (which-key and length revealing) encryption schemes based on computational complexity.

Hydroxyquinoline derived vanadium(IV and V) and copper(II) complexes as potential anti-tuberculosis and anti-tumor agents

Several mixed ligand vanadium and copper complexes were synthesized containing 8-hydroxyquinoline (8HQ) and a ligand such as picolinato (pic(-)), dipicolinato (dipic(2-)) or a Schiff base. The complexes were characterized by spectroscopic techniques and by single-crystal X-ray diffraction in the case of [V(V)O(L-pheolnaph-im)(5-Cl-8HQ)] and [V(V)O(OMe)(8HQ)2], which evidenced the distorted octahedral geometry of the complexes. The electronic absorption data showed the presence of strong ligand to metal charge transfer bands, significant solvent effects, and methoxido species in methanol, which was further confirmed by (51)V-NMR spectroscopy. The structures of [Cu(II)(dipic)(8HQ)]Na and [V(IV)O(pic)(8HQ)] were confirmed by EPR spectroscopy, showing only one species in solution. The biological activity of the compounds was assessed through the minimal inhibitory concentration (MIC) of the compounds against Mycobacterium tuberculosis (Mtb) and the cytotoxic activity against the cisplatin sensitive/resistant ovarian cells A2780/A2780cisR and the non-tumorigenic HEK cells (IC50 values). Almost all tested vanadium complexes were very active against Mtb and the MICs were comparable to, or better than, the MICs of drugs, such as streptomycin. The activity of the complexes against the A2780 cell line was dependent on incubation time presenting IC50 values in the 3-14 μM (at 48 h) range. In these conditions, the complexes were significantly (*P<0.05-**P<0.001) more active than cisplatin (22 μM), in the A2780 cells and even surpassing its activity in the cisplatin-resistant cells A2780cisR (2.4-8 μM vs. 75.4; **P<0.001). In the non-tumorigenic HEK cells poor selectivity toward cancer cells for most of the complexes was observed, as well as for cisplatin.

Amino Alcohol-Derived Reduced Schiff Base VIVO and VV Compounds as Catalysts for Asymmetric Sulfoxidation of Thioanisole with Hydrogen Peroxide

We report the synthesis and characterization of several amino alcohol-derived reduced Schiff base ligands (AORSB) and the corresponding V(IV)O and V(V) complexes. Some of the related Schiff base variants (amino alcohol derived Schiff base = AOSB) were also prepared and characterized. With some exceptions, all compounds are formulated as dinuclear compounds {V(IV)O(L)}(2) in the solid state. Suitable crystals for X-ray diffraction were obtained for two of the AORSB compounds, as well as a rare X-ray structure of a chiral V(IV)O compound, which revealed a dinuclear {V(IV)O(AOSB)}(2) structure with a rather short V-V distance of 3.053(9) Å. Electron paramagnetic resonance (EPR), (51)V NMR, and density functional theory (DFT) studies were carried out to identify the intervenient species prior to and during catalytic reactions. The quantum-chemical DFT calculations were important to determine the more stable isomers in solution, to explain the EPR data, and to assign the (51)V NMR chemical shifts. The V(AORSB) and V(AOSB) complexes were tested as catalysts in the oxidation of thioanisole, with H(2)O(2) as the oxidant in organic solvents. In general, high conversions of sulfoxide were obtained. The V(AOSB) systems exhibited greater activity and enantioselectivity than their V(AORSB) counterparts. Computational and spectroscopic studies were carried out to assist in the understanding of the mechanistic aspects and the reasons behind such marked differences in activity and enantioselectivity. The quantum-chemical calculations are consistent with experimental data in the assessment of the differences in catalytic activity between V(AOSB) and V(AORSB) peroxido variants because the V(AORSB) peroxido transition states correspond to ca. 22 kJ/mol higher energy activation barriers than their V(AOSB) counterparts.

Cryptographically sound implementations for communicating processes

We design a core language of principals running distributed programs over a public network. Our language is a variant of the pi calculus, with secure communications, mobile names, and high-level certificates, but without any explicit cryptography. Within this language, security properties can be conveniently studied using trace properties and observational equivalences, even in the presence of an arbitrary (abstract) adversary With some care, these security properties can be achieved in a concrete setting, relying on standard cryptographic primitives and computational assumptions, even in the presence of an adversary modeled as an arbitrary probabilistic polynomial-time algorithm. To this end, we develop a cryptographic implementation that preserves all properties for all safe programs. We give a series of soundness and completeness results that precisely relate the language to its implementation

Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

Soundness and completeness of formal encryption: The cases of key cycles and partial information leakage

In their seminal work, Abadi and Rogaway show that the formal (Dolev-Yao) notion of indistinguishability is sound with respect to the computational model: messages that are indistinguishable in the formal model become indistinguishable messages in the computational model. However, this result leaves two problems unsolved. First, it cannot tolerate key cycles. Second, it makes the too-strong assumption that the underlying cryptography hides all aspects of the plaintext, including its length. In this paper we extend their work in order to address these problems. We show that the recently-introduced notion of KDM-security can provide soundness even in the presence of key cycles. For this, we have to consider encryption that reveals the length of plaintexts, which we use to motivate a general examination information-leaking encryption. In particular, we consider the conditions under which an encryption scheme that may leak some partial information will provide soundness and completeness to some (possibly weakened) version of the formal model. Partially supported by FCT grant SFRH/BD/8148/2002. Additional support from FEDER/FCT projects QuantLog POCI/MAT/55796/2004, QSec PTDC/EIA/67661/2006 and KLog PTDC/MAT/68723/2006. Partially supported by OSD/ONR CIP/SW URI “Software Quality and Infrastructure Protection for Diffuse Computing” through ONR Grant N00014-01-1-0795. Additional support from NSF Grant CNS-0429689. Additional support from the Packard Fellowship. Part of this work was done while the author was affiliated with University of Pennsylvania, Department of Mathematics. Partially supported by OSD/ONR CIP/SW URI “Software Quality and Infrastructure Protection for Diffuse Computing” through ONR Grant N00014-01-1-0795 and OSD/ONR CIP/SW URI “Trustworthy Infrastructure, Mechanisms, and Experimentation for Diffuse Computing” through ONR Grant N00014-04-1-0725. Additional support from NSF Grants CCR-0098096 and CNS-0429689.

A Process Algebra for Reasoning About Quantum Security

We present a process algebra for specifying and reasoning about quantum security protocols. Since the computational power of the protocol agents must be restricted to quantum polynomial-time, we introduce the logarithmic cost quantum random access machine (QRAM) similar to [S.A. Cook, R.A. Reckhow, Time bounded random access machines, Journal of Computer and System Sciences 7 (1973) 354-375, E. Knill, Conventions for quantum pseudocode, Technical Report LAUR-96-2724, Los Alamos National Laboratory (1996)], and incorporate it in the syntax of the algebra. Probabilistic transition systems give the semantic for the process algebra. Term reduction is stochastic because quantum computation is probabilistic and, moreover, we consider a uniform scheduler to resolve non-deterministic choices. With the purpose of defining security properties, we introduce observational equivalence and quantum computational indistinguishability, and show that the latter is a congruence relation. A simple corollary of this result asserts that any security property defined via emulation is compositional. Finally, we illustrate our approach by establishing the concept of quantum zero-knowledge protocol.