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of the Differential Fault Analysis (DFA) of AES by developing an inter
relationship between conventional cryptanalysis of AES and DFAs. We
show that the existing attacks have not reached these limits and present techniques to reach these. More specifically, we propose optimal DFA on states of AES-128 and AES-256. We also propose attacks on the key schedule of the three versions of AES, and demonstrate that these are some of the most efficient attacks on AES to date. Our attack on AES-128 key schedule is optimal, and the attacks on AES-192 and AES-256 key schedule are very close to optimal. Detailed experimental results have been provided for the developed attacks. The work has been compared to other works and also the optimal limits of Differential Fault Analysis of AES.
by a group of message recipients in the network coding setting. That is, a sender generates an
A-code over a message such that any intermediate node or recipient can check the authenticity
of the message, typically to detect pollution attacks. We call such an A-code as multi-receiver
homomorphic A-code (MRHA-code). In this paper, we first formally define an MRHA-code.
We then derive some lower bounds on the security parameters and key sizes associated with our
MRHA-codes. Moreover, we give efficient constructions of MRHA-code schemes that can be used
to mitigate pollution attacks on network codes. Unlike prior works on computationally secure
homomorphic signatures and MACs for network coding, our MRHA-codes achieve unconditional
We ask whether similar negative results also hold for a more recent notion of privacy called differential privacy (Dwork et al., TCC\'06), concentrating, in particular, on achieving differential privacy with the Santha-Vazirani source. We show that the answer is no. Specifically, we give a differentially private mechanism for approximating arbitrary \"low sensitivity\" functions that works even with randomness coming from a gamma-Santha-Vazirani source, for any gamma
The first result of this submission consists in defining ``secure\'\' database commitment and in observing that previous constructions do not satisfy this definition. This leaves open the question of whether there is any way this functionality can be achieved.
We then provide an affirmative answer to this question by using new techniques that combined together achieve ``secure\'\' database commitment. Our construction is in particular optimized to require only a constant number of rounds, to provide non-interactive proofs on the content of the database, and to rely only on the existence of a family of CRHFs. This is the first result where input-size hiding secure computation is achieved for an interesting functionality and moreover we obtain this result with standard security (i.e., simulation in expected polynomial time against fully malicious adversaries, without random oracles, non-black-box extraction assumptions, hardness assumptions against super-polynomial time adversaries, or other controversial/strong assumptions).
A key building block in our construction is a universal argument enjoying an improved proof of knowledge property, that we call quasi-knowledge. This property is significantly closer to the standard proof of knowledge property than the weak proof of knowledge property satisfied by previous constructions.
- Revocable Storage. We ask how a third party can process a ciphertext to disqualify revoked users from accessing data that was encrypted in the past, while the user still had access. In applications, such storage may be with an untrusted entity and as such, we require that the ciphertext management operations can be done without access to any sensitive data (which rules out decryption and re-encryption). We define the problem of revocable storage and provide a fully secure construction. Our core tool is a new procedure that we call ciphertext delegation. One can apply ciphertext delegation on a ciphertext encrypted under a certain access policy to `re-encrypt\' it to a more restrictive policy using only public information. We provide a full analysis of the types of delegation possible in a number of existing ABE schemes.
- Protecting Newly Encrypted Data. We consider the problem of ensuring that newly encrypted data is not decryptable by a user\'s key if that user\'s access has been revoked. We give the first method for obtaining this revocation property in a fully secure ABE scheme. We provide a new and simpler approach to this problem that has minimal modications to standard ABE. We identify and define a simple property called piecewise key generation which gives rise to efficient revocation. We build such solutions for Key-Policy and Ciphertext-Policy Attribute-Based Encryption by modifying an existing ABE scheme due to Lewko et al. to satisfy our piecewise property and prove security in the standard model.
It is the combination of our two results that gives an approach for revocation. A storage server can update stored ciphertexts to disqualify revoked users from accessing data that was encrypted before the user\'s access was revoked. This is the full version of the Crypto 2012 paper.