@article {15117,
	title = {Which Languages Have 4-Round Zero-Knowledge Proofs?},
	journal = {Journal of cryptology},
	volume = {25},
	year = {2012},
	month = {2012///},
	pages = {41 - 56},
	abstract = {We show that if a language L has a 4-round, black-box, computational zero-knowledge proof system with negligible soundness error, then . Assuming the polynomial hierarchy does not collapse, this means in particular that NP-complete languages do not have 4-round zero-knowledge proofs with black-box simulation.},
	doi = {10.1007/s00145-010-9081-y},
	author = {Katz, Jonathan}
}
