Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Advances in Concrete Cryptanalysis of Lattice Problems and Interactive Signature Schemes(2024) Kippen, Hunter Michael; Dachman-Soled, Dana; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Advanced cryptography that goes beyond what is currently deployed to service our basic internet infrastructure is continuing to see widespread adoption. The enhanced functionality achieved by these schemes frequently yields an increase in complexity. Solely considering the asymptotic security of the underlying computational assumptions is often insufficient to realize practical and secure instantiations.In these cases, determining the risk of any particular deployment involves analyzing the concrete security (the exact length of time it would take to break the encryption) as well as quantifying how concrete security can degrade over time due to any exploitable information leakage. In this dissertation, we examine two such cryptographic primitives where assessing concrete security is paramount. First, we consider the cryptanalysis of lattice problems (used as the basis for current standard quantum resistant cryptosystems). We develop a novel side-channel attack on the FrodoKEM key encapsulation mechanism as submitted to the NIST Post Quantum Cryptography (PQC) standardization process. Our attack involves poisoning the FrodoKEM Key Generation (KeyGen) process using a security exploit in DRAM known as “Rowhammer”. Additionally, we revisit the security of the lattice problem known as Learning with Errors (LWE) in the presence of information leakage. We further enhance the robustness of prior methodology by viewing side information from a geometric perspective. Our approach provides the rigorous promise that, as hints are integrated, the correct solution is a (unique) lattice point contained in an ellipsoidal search space. Second, we study the concrete security of interactive signature schemes (used as part of many Privacy Enhancing Technologies). To this end, we complete a new analysis of the performance of Wagner’s k-list algorithm [CRYPTO ‘02], which has found significant utility in computing forgeries on several interactive signature schemes that implicitly rely on the hardness of the ROS problem formulated by Schnorr [ICICS ‘01].Item Frontiers in Lattice Cryptography and Program Obfuscation(2017) Apon, Daniel Christopher; Katz, Jonathan; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, we explore the frontiers of theory of cryptography along two lines. In the first direction, we explore Lattice Cryptography, which is the primary sub-area of post-quantum cryptographic research. Our first contribution is the construction of a deniable attribute-based encryption scheme from lattices. A deniable encryption scheme is secure against not only eavesdropping attacks as required by semantic security, but also stronger coercion attacks performed after the fact. An attribute-based encryption scheme allows ``fine-grained'' access to ciphertexts, allowing for a decryption access policy to be embedded in ciphertexts and keys. We achieve both properties simultaneously for the first time from lattices. Our second contribution is the construction of a digital signature scheme that enjoys both short signatures and a completely tight security reduction from lattices. As a matter of independent interest, we give an improved method of randomized inversion of the G gadget matrix, which reduces the noise growth rate in homomorphic evaluations performed in a large number of lattice-based cryptographic schemes, without incurring the high cost of sampling discrete Gaussians. In the second direction, we explore Cryptographic Program Obfuscation. A program obfuscator is a type of cryptographic software compiler that outputs executable code with the guarantee that ``whatever can be hidden about the internal workings of program code, is hidden.'' Indeed, program obfuscation can be viewed as a ``universal and cryptographically-complete'' tool. Our third contribution is the first, full-scale implementation of secure program obfuscation in software. Our toolchain takes code written in a C-like programming language, specialized for cryptography, and produces secure, obfuscated software. Our fourth contribution is a new cryptanalytic attack against a variety of ``early'' program obfuscation candidates. We provide a general, efficiently-testable property for any two branching programs, called partial inequivalence, which we show is sufficient for launching an ``annihilation attack'' against several obfuscation candidates based on Garg-Gentry-Halevi multilinear maps.