1,721,078 research outputs found
On Secure Bulletin Boards for E-Voting
Get PDFPeaaegu iga elektroonilise hääletamise protokolli esimeseks etapiks on häälte kogumine ning nende talletamine. Seda teenust pakub teadetetahvlisüsteem (bulletin board). Paljud teadusartiklid eeldavad turvalise teadetetahvlisüsteemi olemasolu, kuid konkreetseid süsteeme on välja pakutud vähe. Tihti eeldatakse, et teadetetahvlisüsteem on tsentraalne usaldatav osapool, kuid hiljutistes töödes on tähelepanu juhitud tõrkekindla hajustalletuse olulisusele. Käesolevas töös pakume välja formaalse mudeli teadetetahvlisüsteemi funktsionaalsuse ning turvalisuse analüüsimisseks. Meie mudeli aluseks on Culnane ja Schneideri poolt konverentsil Computer Security Foundations Symposium 2014 väljapakutud teadetetahvlisüsteemi omadused. Me käsitleme turvalist teadetetahvlisüsteemi kui Garay ja teiste poolt konverentsil Eurocrypt 2015 tutvustatud avalikku tehingute pearaamatut, mis õnnestunud hääle talletamise korral väljastab kviitungi. Täpsemalt, me defineerime omadused (tõendatav) püsivus ning tõendatav elusus.Me analüüsime Culnane ja Schneideri väljapakutud teadetetahvlisüsteemi turvalisust ning näitame, et nende protokolli korral ei ole elususe omadus täidetud, kui mõni kogumisneel (item collection peer) on ebaaus. Nende süsteem saavutab tõendatava püsivuse kasutades triviaalset lävisignatuuri juhul, kui ebaausaid kogumisneele on <N/3, vastasel korral on tõke <N/4. Culnane ja Schneideri teadetetahvlisüsteemist motiveeritult pakume välja uue süsteemi, mille korral on tagatud nii tõendatav püsivus kui ka tõendatav elusus, kui ebaausaid kogumisneele on vastavalt <N/3 ning <N/2. Lisaks on meie protokoll lihtne suhtluskeerukuselt. Antud töö põhineb konverentsile esitatud artiklil „A Cryptographic Approach to Bulletin Boards“ („Krüptograafiline lähenemine teadetetahvlisüsteemidele“), mille kaasautoriteks on Aggelos Kiayas, Helger Lipmaa, Janno Siim ja Thomas Zacharias.Vote collection together with storage of collected votes is the first phase of practically any electronic voting (e-voting) protocol. This functionality is provided by a bulletin board system. Many research papers in e-voting require the existence of a secure bulletin board, but there are only a few concrete systems. In the literature it is common to assume that bulletin board is a centralized trusted party, but in recent works the importance of a distributed fault-tolerant bulletin board has been raised. In this thesis, we propose a formal model for analysis of security and functionality of a bulletin board system motivated by the security requirements Culnane and Schneider introduced in Computer Security Foundations Symposium 2014. We consider a secure bulletin board as a robust public transaction ledger presented by Garay et al. in Eurocrypt 2015 that additionally provides receipts for successful postings. More precisely, we introduce two properties: (Confirmable) Persistence and Confirmable Liveness. We study a bulletin board system proposed by Culnane and Schneider in our model, and show that their protocol does not achieve Confirmable Liveness if there exist corrupted item collection peers, but achieves Confirmable Persistence for <N/3 corrupted item collection peers using only our trivial threshold signature scheme, otherwise the bound is <N/4. Motivated by the security analysis of Culnane-Schneider bulletin board system, we propose a fully secure bulletin board system and prove that it tolerates <N/3 corrupted item collection peers for Confirmable Persistence and <N/2 corrupted item collection peers for Confirmable Liveness. This thesis is based on a submitted paper "A Cryptographic Approach to Bulletin Boards" with co-authors Aggelos Kiayas, Helger Lipmaa, Janno Siim and Thomas Zacharias
Privacy-Preserving Horizontally Partitioned Linear Programs
Get PDFWe propose a simple privacy-preserving reformulation of a linear program whose equality constraint
matrix is partitioned into groups of rows. Each group of matrix rows and its corresponding right hand side
vector are owned by a distinct private entity that is unwilling to share ormake public its row group or right hand
side vector. By multiplying each privately held constraint group by an appropriately generated and privately
held random matrix, the original linear program is transformed into an equivalent one that does not reveal any
of the privately held data or make it public. The solution vector of the transformed secure linear program is
publicly generated and is available to all entities
Privacy-Preserving Linear and Nonlinear Approximation via Linear Programming
Get PDFWe propose a novel privacy-preserving random kernel approximation based on a data matrix
A ? Rm�n whose rows are divided into privately owned blocks. Each block of rows belongs to
a different entity that is unwilling to share its rows or make them public. We wish to obtain an
accurate function approximation for a given y ? Rm corresponding to each of the m rows of A. Our
approximation of y is a real function on Rn evaluated at each row of A and is based on the concept of
a reduced kernel K(A,B?) where B? is the transpose of a completely random matrix B. The proposed
linear-programming-based approximation, which is public but does not reveal the privately-held data
matrix A, has accuracy comparable to that of an ordinary kernel approximation based on a publicly
disclosed data matrix A
Private Branching Programs: On Communication-Efficient Cryptocomputing
Get PDFWe polish a recent cryptocomputing method of Ishai and Paskin from TCC 2007. More precisely, we show that every function can be cryptocomputed in communication, linear in the product of client\u27s input length and the length of the branching program, and computation, linear in the size of the branching program that computes it. The method is based on the existence of a communication-efficient -CPIR protocol. We give several nontrivial applications, including: (a) improvement on the communication of Lipmaa\u27s CPIR protocol, (b) a CPIR protocol with log-squared communication and sublinear server-computation by giving a secure function evaluation protocol for Boolean functions with similar performance, (c) a protocol for PIR-writing with low amortized complexity, (d) a selective private function evaluation (SPFE) protocol. We detail one application of SPFE that makes it possible to compute how similar is client\u27s input to an element in server\u27s database, without revealing any information to the server. For SPFE, we design a -message extension of the basic protocol that is efficient for a large class of functionalities
New communication-efficient oblivious transfer protocols based on pairings. Cryptology ePrint Archive, Report 2007/133
No full textAbstract. We construct two simple families of two-message (n, 1)-oblivious transfer protocols based on degree-t homomorphic cryptosystems with the communication of respectively 1 + ⌈n/t ⌉ and 3 + ⌈n/(t + 1) ⌉ ciphertexts. The construction of both families relies on efficient cryptocomputable conditional disclosure of secret protocols; the way this is done may be of independent interest. The currently most interesting case t = 2 can be based on the Boneh-Goh-Nissim cryptosystem. We show how to reduce the communication of virtually any existing oblivious transfer protocols by proposing a new related communicationefficient generic transformation from computationally-private information retrieval protocols to oblivious transfer protocols. Keywords. Computationally-private information retrieval, conditional disclosure of secrets, homomorphic encryption, oblivious transfer.
Prover-Efficient Commit-And-Prove Zero-Knowledge SNARKs
Get PDFZk-SNARKs (succinct non-interactive zero-knowledge arguments of knowledge) are needed in many applications. Unfortunately, all previous zk-SNARKs for interesting languages are either inefficient for the prover, or are non-adaptive and based on a commitment scheme that depends both on the prover\u27s input and on the language, i.e., they are not commit-and-prove (CaP) SNARKs. We propose a proof-friendly extractable commitment scheme, and use it to construct prover-efficient adaptive CaP succinct zk-SNARKs for different languages, that can all reuse committed data. In new zk-SNARKs, the prover computation is dominated by a linear number of cryptographic operations. We use batch-verification to decrease the verifier\u27s computation; importantly, batch-verification can be used also in QAP-based zk-SNARKs
On Diophantine Complexity and Statistical Zero-Knowledge Arguments
No full textWe show how to construct practical honest-verifier statistical zero-knowledge Diophantine arguments of knowledge (HVSZK AoK) that a committed tuple of integers belongs to an arbitrary language in bounded arithmetic. While doing this, we propose a new algorithm for computing the Lafgrange representation of nonnegative integers and a new eficient representing polynomial for the exponential relation. We apply our results by constructing the most efficient known HVSZK AoK for non-negativity and the first constant-round practical HVSZK AoK for exponential relation. Finally, we propose the outsourcing model for cryptographic protocols and design communication-efficient versions of the Damgard-Jurik multi-candidate voting scheme and of the Lipmaa-Asokan-Niemi (b + 1)st-price auction scheme that work in this model
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