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We present a Hierarchical Identity Based Encryption (HIBE) system where the ciphertext consists of just three group elements and decryption requires only two bilinear map computations, regardless of the hierarchy depth. Encryption is as efficient as in other HIBE systems. We prove that the scheme is selective-ID secure in the standard model and fully secure(More)
Let ψ be a 2-DNF formula on boolean variables x1, . . . , xn ∈ {0, 1}. We present a homomorphic public key encryption scheme that allows the public evaluation of ψ given an encryption of the variables x1, . . . , xn. In other words, given the encryption of the bits x1, . . . , xn, anyone can create the encryption of ψ(x1, . . . , xn). More generally, we can(More)
Address-space randomization is a technique used to fortify systems against buffer overflow attacks. The idea is to introduce artificial diversity by randomizing the memory location of certain system components. This mechanism is available for both Linux (via PaX ASLR) and OpenBSD. We study the effectiveness of address-space randomization and find that its(More)
A secure index is a data structure that allows a querier with a “trapdoor” for a word x to test in O(1) time only if the index contains x; The index reveals no information about its contents without valid trapdoors, and trapdoors can only be generated with a secret key. Secure indexes are a natural extension of the problem of constructing data structures(More)
Privacy-preserving protocols allow multiple parties with private inputs to perform joint computation while preserving the privacy of their respective inputs. An important cryptographic primitive for designing privacy-preserving protocols is secure function evaluation (SFE). The classic solution for SFE by Yao uses a gate representation of the function that(More)
We propose and analyze two efficient signature schemes whose security is tightly related to the Diffie-Hellman problems in the random oracle model. The security of our first scheme relies on the hardness of the computational Diffie-Hellman problem; the security of our second scheme - which is more efficient than the first-is based on the hardness of the(More)
Encryption schemes are designed to provide data confidentiality and are a fundamental cryptographic primitive with many applications in higher-level protocols. Groups with a bilinear map allow us to build public key encryption schemes with new properties that are otherwise difficult to obtain using groups without a bilinear map. We support our thesis by(More)
We examine covert channels in privacy-enhanced mobile identification devices where the devices uniquely identify themselves to an authorized verifier. Such devices (e.g. RFID tags) are increasingly commonplace in hospitals and many other environments. For privacy, the device outputs used for identification should "appear random" to any entity other than the(More)