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We address the question of whether or not semantically secure public-key encryption primitives imply the existence of chosen ci-phertext attack (CCA) secure primitives. We show a black-box separation , following the methodology introduced by Impagliazzo and Rudich [23], for a large non-trivial class of constructions. In particular, we show that if the(More)
A central focus of modern cryptography is the construction of efficient, " high-level " cryptographic tools (e.g., encryption schemes) from weaker, " low-level " cryptographic primitives (e.g., one-way functions). Of interest are both the existence of such constructions , and their efficiency. Here, we show essentially-tight lower bounds on the best(More)
Children use syntax to interpret sentences and learn verbs; this is syntactic bootstrapping. The structure-mapping account of early syntactic bootstrapping proposes that a partial representation of sentence structure, the set of nouns occurring with the verb, guides initial interpretation and provides an abstract format for new learning. This account(More)
A fundamental task in sentence comprehension is to assign semantic roles to sentence constituents. The structure-mapping account proposes that children start with a shallow structural analysis of sentences: children treat the number of nouns in the sentence as a cue to its semantic predicate-argument structure, and represent language experience in an(More)
A fundamental step in sentence comprehension involves assigning semantic roles to sentence constituents. To accomplish this, the listener must parse the sentence, find constituents that are candidate arguments , and assign semantic roles to those constituents. Each step depends on prior lexical and syntactic knowledge. Where do children learning their first(More)
Theories of human language acquisition assume that learning to understand sentences is a partially-supervised task (at best). Instead of using 'gold-standard' feedback, we train a simplified " Baby " Semantic Role Labeling system by combining world knowledge and simple grammatical constraints to form a potentially noisy training signal. This combination of(More)
Children quickly acquire basic grammatical facts about their native language. Does this early syntactic knowledge involve knowledge of words or rules? According to lexical accounts of acquisition, abstract syntactic and semantic categories are not primitive to the language-acquisition system; thus, early language comprehension and production are based on(More)
Private information retrieval (PIR) schemes provide a user with information from a database while keeping his query secret from the database manager. We propose a new model for PIR, utilizing auxiliary random servers providing privacy services for database access. The principal database initially engages in a preprocessing setup computation with the random(More)