Anonymous credential schemes enable service providers to verify information that a credential holder willingly discloses, without needing any further personal data to corroborate that information, and without allowing the user to be tracked from one interaction to the next. Mercurial signatures are a novel class of anonymous credentials which show good promise as a simple and efficient construction without heavy reliance on zero-knowledge proofs. However, they still require significant development in order to achieve the functionality that most existing anonymous credential schemes provide. Encoding multiple attributes of the credential holder in such a way that they can be disclosed selectively with each use of the credential is often seen as a vital feature of anonymous credentials, and is one that mercurial signatures have not yet implemented. In this paper, we show a simple way to encode attributes in a mercurial signature credential and to regulate which attributes a credential holder can issue when delegating their credential to another user. We also extend the security model associated with mercurial signatures to account for the inclusion of attributes, and prove the security of our extension with respect to the original mercurial signature construction.
In this work, we extend the MPC-in-the-Head framework, used in recent efficient zero-knowledge protocols, to work over the ring ℤ_2^k , which is the primary operating domain for modern CPUs. The proposed schemes are compatible with any threshold linear secret sharing scheme and draw inspiration from MPC protocols adapted for ring operations. Additionally, we explore various batching methodologies, leveraging Shamir’s secret sharing schemes and Galois ring extensions, and show the applicability of our approach in RAM program verification. Finally, we analyse different options for instantiating the resulting ZK scheme over rings and compare their communication costs.
Low Rank Parity Check (LRPC) codes form a class of rank-metric error-correcting codes that was purposely introduced to design public-key encryption schemes. An LRPC code is defined from a parity check matrix whose entries belong to a relatively low dimensional vector subspace of a large finite field. This particular algebraic feature can then be exploited to correct with high probability rank errors when the parameters are appropriately chosen. In this paper, we present theoretical upper-bounds on the probability that the LRPC decoding algorithm fails.
The notion of coset leader has applications in coding theory and cryptography. It has been studied in several papers. In this paper, we extend a recent study, made on the coset leaders of the first order Reed-Muller codes, to two classes of Boolean functions which have played an important role in diverse domains of Boolean functions, and whose study was missing in this context. We characterize the coset leaders that belong to the classes of Niho functions and threshold functions (this second class being a generalization of the class of majority functions).
The FBC block cipher is an award-winning algorithm of the recent Cryptographic Algorithm Design Competition in China, which has three versions: FBC128-128 with a 128-bit block size and a 128-bit key size, FBC128-256 with a 128-bit block size and a 256-bit key size, and FBC256 with a 256-bit block size and a 256-bit key size. The best previously published cryptanalysis results on FBC are an impossible differential attack on 13-round FBC128-128 and a boomerang attack on 13-round FBC128-256. In this paper, we exploit a 12-round rectangle distinguisher with probability $$2^{-234}$$ of FBC128 and a 16-round rectangle distinguisher with probability $$2^{-448}$$ of FBC256, and observe that preliminary satisfying ciphertext quartets can be efficiently filtered out by sorting plaintext pairs according to some nibble positions at the ciphertext side during key-recovery phase, and finally we mount rectangle attacks on 14-round FBC128-128, 15-round FBC128-256 and 19-round FBC256 to recover their respective user key. Our attacks break more rounds than any previously published attacks on FBC.
