Structure-Preserving Compilers from New Notions of Obfuscations

The dream of software obfuscation is to take programs, as they are, and then generically compile them into obfuscated versions that hide their secret inner workings. In this work we investigate notions of obfuscations weaker than virtual black-box (VBB) but which still allow obfuscating cryptographic primitives preserving their original functionalities as much as possible. In particular we propose two new notions of obfuscations, which we call oracle-differing-input obfuscation (odiO) and oracle-indistinguishability obfuscation (oiO). In a nutshell, odiO is a natural strengthening of differing-input obfuscation (diO) and allows obfuscating programs for which it is hard to find a differing-input when given only oracle access to the programs. An oiO obfuscator allows to obfuscate programs that are hard to distinguish when treated as oracles. We then show applications of these notions, as well as positive and negative results around them. A few highlights include: – Our new notions are weaker than VBB and stronger than diO. – As it is the case for VBB, we show that there exist programs that cannot be obfuscated with odiO or oiO. – Our new notions allow to generically compile several flavours of secret-key primitives (e.g., SKE, MAC, designated verifier NIZK) into their public-key equivalent (e.g., PKE, signatures, publicly verifiable NIZK) while preserving one of the algorithms of the original scheme (function-preserving), or the structure of their outputs (format-preserving)

Basing Obfuscation on Simple Tamper-Proof Hardware Assumptions

Code obfuscation is one of the most powerful concepts in cryptography. It could yield functional encryption, digital rights management, and maybe even secure cloud computing. However, general code obfuscation has been proven impossible and the research then focused on obfuscating very specific functions, studying weaker security definitions for obfuscation, and using tamper-proof hardware tokens to achieve general code obfuscation. Following this last line this work presents the first scheme which bases general code obfuscation of multiple programs on one single stateless hardware token. Our construction is proven secure in the UC-framework and proceeds in three steps: 1. We construct an obfuscation scheme based on fully homomorphic encryption (FHE) and a hybrid functionality conditional decrypt, which decrypts the result of a homomorphic computation given a proof that the computation was performed as intended. One difficulty of the first step are possible decryptions errors in the FHE. These decryption errors can occur whenever the randomness for the encryption is chosen maliciously by the receiver of the obfuscated code. Such decryption errors then could make a real obfuscated computation distinguishable from a black box use of the non-obfuscated program. 2. Given two common reference strings (CRS) we construct a UC-protocol realizing the functionality conditional decrypt with a stateless hardware token. As the token is stateless it is resettable by a dishonest receiver and the proofs given to the token must be resettably sound. One additional difficulty occurs when the issuer of the token can be corrupted. A malicious token can be stateful and it cannot be prevented that it aborts after a hardwired number of invocations. To prevent adaptive behavior of a malicious token the data of the receiver has to be hidden from the token and the proofs given to the token must even hide the size of the program and the length of the computation. 3. Last we construct a protocol constructing a CRS with a stateless hardware token. Care has to be taken here to not let the token learn anything about the resulting CRS which could not be simulated, because the very same token will later be used in a protocol based on the security of this CRS

Advances in cryptographic voting systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 241-254).Democracy depends on the proper administration of popular elections. Voters should receive assurance that their intent was correctly captured and that all eligible votes were correctly tallied. The election system as a whole should ensure that voter coercion is unlikely, even when voters are willing to be influenced. These conflicting requirements present a significant challenge: how can voters receive enough assurance to trust the election result, but not so much that they can prove to a potential coercer how they voted? This dissertation explores cryptographic techniques for implementing verifiable, secret-ballot elections. We present the power of cryptographic voting, in particular its ability to successfully achieve both verifiability and ballot secrecy, a combination that cannot be achieved by other means. We review a large portion of the literature on cryptographic voting. We propose three novel technical ideas: 1. a simple and inexpensive paper-base cryptographic voting system with some interesting advantages over existing techniques, 2. a theoretical model of incoercibility for human voters with their inherent limited computational ability, and a new ballot casting system that fits the new definition, and 3. a new theoretical construct for shuffling encrypted votes in full view of public observers.by Ben Adida.Ph.D

LIPIcs, Volume 251, ITCS 2023, Complete Volume

LIPIcs, Volume 251, ITCS 2023, Complete Volum