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A block cipher is the foundation stone of symmetric-key cryptography. Due to its simplicity and high performance, it is often the workhorse for providing confidentiality - one of the primary goals of cryptography. Hence the security of a block cipher is of fundamental importance in the entire infrastructure of cryptography, and therefore block ciphers shall be analyzed and evaluated. This practice is called block cipher cryptanalysis. In this thesis, we analyze a few block ciphers in the classic meet-in-the-middle model and in the recently proposed multidimensional linear cryptanalysis model.
Besides for encryption, block ciphers are also one of the most versatile building blocks used for constructing many other cryptographic primitives. One such example is the compression function of cryptographic hash functions, and there is a close relation between the security analysis of block ciphers and hash functions. In addition, many dedicated cryptographic hash functions are designed with ideas used in block ciphers. Therefore, it is natural that many block cipher cryptanalysis techniques can be transferred to hash function analysis. In this thesis, we analyze hash functions with differential cryptanalysis and techniques inspired by differential cryptanalysis. On the other hand, recent advances in hash function cryptanalysis contribute to the analysis of block ciphers. We give one such example too.
In total we have four main topics on (or closely related to) the security analysis of block ciphers.
ranging from fast and generic symmetric ciphers to compact public key and white-box constructions based on generic affine transformations combined with specially designed low degree non-linear layers. While explaining our design process we show several instructive attacks on the
weaker variants of our schemes.
(ABE) schemes for all boolean circuits. GVW show that TOR schemes can be constructed assuming the hardness of the learning-with-errors (LWE) problem.
We propose a slightly weaker variant of TOR schemes called correlation-relaxed two-to-one recoding (CR-TOR). Unlike the TOR schemes, our weaker variant does not require an encoding function to
be pseudorandom on correlated inputs. We instead replace it with an indistinguishability property that states a ciphertext is hard to decrypt without access to a certain encoding. The primary benefit of this relaxation is that it allows the construction of ABE for circuits using the TOR paradigm from a broader class of cryptographic assumptions.
We show how to construct a CR-TOR scheme from the noisy cryptographic multilinear maps of Garg, Gentry, and Halevi as well as those of Coron, Lepoint, and Tibouchi. Our framework leads to an instantiation of ABE for circuits that is conceptually different from the existing constructions.