Theory and Applications of Outsider Anonymity in Broadcast Encryption

Broadcast Encryption (BE) allows efficient one-to-many secret communication of data over a broadcast channel. In the standard setting of BE, information about receivers is transmitted in the clear together with ciphertexts. This could be a serious violation of recipient privacy since the identities of the users authorized to access the secret content in certain broadcast scenarios are as sensitive as the content itself. Anonymous Broadcast Encryption (AnoBe) prevents this leakage of recipient identities from ciphertexts but at a cost of a linear lower bound (in the number of receivers) on the length of ciphertexts. A linear ciphertext length is a highly undesirable bottleneck in any large-scale broadcast application. In this thesis, we propose a less stringent yet very meaningful notion of anonymity for anonymous broadcast encryption called Outsider-Anonymous Broadcast Encryption (oABE) that allows the creation of ciphertexts that are sublinear in the number of receivers. We construct several oABE schemes with varying security guarantees and levels of efficiency. We also present two very interesting cryptographic applications afforded by the efficiency of our oABE schemes. The first is Broadcast Steganography (BS), the extension of the state of the art setting of point-to-point steganography to the multi-recipient setting. The second is Oblivious Group Storage (OGS), the introduction of fine-grained data access control policies to the setting of multi-client oblivious cloud storage protocols

Attribute-based encryption for cloud computing access control: A survey

National Research Foundation (NRF) Singapore; AXA Research Fun

Towards Black-Box Accountable Authority IBE with Short Ciphertexts and Private Keys

At Crypto'07, Goyal introduced the concept of Accountable Authority Identity-Based Encryption as a convenient tool to reduce the amount of trust in authorities in Identity-Based Encryption. In this model, if the Private Key Generator (PKG) maliciously re-distributes users' decryption keys, it runs the risk of being caught and prosecuted. Goyal proposed two constructions: the first one is efficient but can only trace well-formed decryption keys to their source; the second one allows tracing obfuscated decryption boxes in a model (called weak black-box model) where cheating authorities have no decryption oracle. The latter scheme is unfortunately far less efficient in terms of decryption cost and ciphertext size. In this work, we propose a new construction that combines the efficiency of Goyal's first proposal with a very simple weak black-box tracing mechanism. Our scheme is described in the selective-ID model but readily extends to meet all security properties in the adaptive-ID sense, which is not known to be true for prior black-box schemes.Comment: 32 page

Single Secret Key Crptosystem for Secure and Efficient Exchange of Data in Cloud

Nowadays users are storing their personal data on a cloud storage because of its numerous advantages. One of the important advantage in cloud storage is sharing of data between users or between organizations. In this paper we propose a simple, flexible, efficient and secure data sharing method for the cloud users. Here we are describing a special type of public key encryption scheme where public key, master-secret key, single secret key and cipher text sizes are constant. Single secret key can be obtained by combining number of secret keys. The sender can securely share multiple files with receiver by encrypting each file using a separate public key. Then the sender will combine all the public keys to form a single secret key which is exchanged with receiver by using Diffie-Hellman algorithm. Advantage of small single secret key is user can store this decryption key on a resource constraint devices like smart cards, smart cell phones or sensor nodes. Receiver can download the number of files by using single secret key

Contributions to Identity-Based Broadcast Encryption and Its Anonymity

Broadcast encryption was introduced to improve the efficiency of encryption when a message should be sent to or shared with a group of users. Only the legitimate users chosen in the encryption phase are able to retrieve the message. The primary challenge in construction a broadcast encryption scheme is to achieve collusion resistance such that the unchosen users learn nothing about the content of the encrypted message even they collude

Efficient semi-static secure broadcast encryption scheme

In this paper, we propose a semi-static secure broadcast encryption scheme with constant-sized private keys and ciphertexts. Our result improves the semi-static secure broadcast encryption scheme introduced by Gentry and Waters. Specifically, we reduce the private key and ciphertext size by half. By applying the generic transformation proposed by Gentry and Waters, our scheme also achieves adaptive security. Finally, we present an improved implementation idea which can reduce the ciphertext size in the aforementioned generic transformation

On the Impossibility of Basing Identity Based Encryption on Trapdoor Permutations

We ask whether an Identity Based Encryption (IBE) sys-tem can be built from simpler public-key primitives. We show that there is no black-box construction of IBE from Trapdoor Permutations (TDP) or even from Chosen Ci-phertext Secure Public Key Encryption (CCA-PKE). These black-box separation results are based on an essential prop-erty of IBE, namely that an IBE system is able to compress exponentially many public-keys into a short public parame-ters string. 1