Nishanth Chandran

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Recently, at Crypto 2008, Boneh, Halevi, Hamburg, and Ostrovsky (BHHO) solved the longstanding open problem of “circular encryption,” by presenting a public key encryption scheme and proving that it is semantically secure against key dependent chosen plaintext attack (KDMCPA security) under standard assumptions (and without resorting to random oracles).(More)
We consider what constitutes identities in cryptography. Typical examples include your name and your social-security number, or your fingerprint/iris-scan, or your address, or your (non-revoked) publickey coming from some trusted public-key infrastructure. In many situations, however, where you are defines your identity. For example, we know the role of a(More)
The Universal Composability framework was introduced by Canetti to study the security of protocols which are concurrently executed with other protocols in a network environment. Unfortunately it was shown that in the so called plain model, a large class of functionalities cannot be securely realized. These severe impossibility results motivated the study of(More)
Ring signatures, introduced by Rivest, Shamir and Tauman, enable a user to sign a message anonymously on behalf of a “ring”. A ring is a group of users, which includes the signer. We propose a ring signature scheme that has size O( √ N) where N is the number of users in the ring. An additional feature of our scheme is that it has perfect anonymity. Our ring(More)
Cryptographic keys must be protected from exposure. In real-world applications, they are often guarded by cryptographic tokens that employ sophisticated hardware-security measures. Several logical attacks on the key management operations of cryptographic tokens have been reported in the past, which allowed to expose keys merely by exploiting the token API(More)
Today, enterprises collect large amounts of data and leverage the cloud to perform analytics over this data. Since the data is often sensitive, enterprises would prefer to keep it confidential and to hide it even from the cloud operator. Systems such as CryptDB and Monomi can accomplish this by operating mostly on encrypted data; however, these systems rely(More)
We study the problem of &#8220;privacy amplification&#8221;: key agreement between two parties who both know a weak secret <i>w</i>, such as a password. (Such a setting is ubiquitous on the internet, where passwords are the most commonly used security device.) We assume that the key agreement protocol is taking place in the presence of an active(More)
In this work, we study position-based cryptography in the quantum setting. The aim is to use the geographical position of a party as its only credential. On the negative side, we show that if adversaries are allowed to share an arbitrarily large entangled quantum state, the task of secure position-verification is impossible. To this end, we prove the(More)
We introduce the notion of locally updatable and locally decodable codes (LULDCs). While, intuitively, updatability and error-correction seem to be contrasting goals, we show that for a suitable, yet meaningful, metric (which we call the Prefix Hamming metric), one can construct such codes. Informally, the Prefix Hamming metric allows the adversary to(More)
In STOC'05, Aim, Hopper and Longford introduced the notion of covert computation. A covert computation protocol is one in which parties am run a protocol without knowing if other parties ore also participating in the protocol or not. At the end of the protocol, if all parties participated in the protocol and if the function output is favorable to all(More)