We show that any concurrent zero-knowledge protocol for a non-trivial
language (i.e., for a language outside $\BPP$), whose security is proven
via black-box simulation, must use at least $\tilde\Omega(\log n)$
rounds of interaction. This result achieves a substantial improvement
over previous lower bounds, and is the first bound to rule ... more >>>

We show that recognizing the $K_3$-freeness and $K_4$-freeness of
graphs is hard, respectively, for two-player nondeterministic
communication protocols with exponentially many partitions and for
nondeterministic (syntactic) read-$s$ times branching programs.

The key ingradient is a generalization of a coloring lemma, due to
Papadimitriou and Sipser, which says that for every ... more >>>

In this paper we give a direct proof of $N_0=N_0^\prime$, i.e., the equivalence of
uniform $NC^1$ based on different recursion principles: one is OR-AND complete
binary tree (in depth $\log n$) and the other is the recursion on notation with value
bounded in $[0,k]$ and $|x|(=n)$ many ... more >>>