In a proof-of-retrievability system, a data storage center convinces a verifier that he is actually storing all of a client's data. The central challenge is to build systems that are both efficient and provably secure--that is, it should be possible to extract the client's data from any prover that passes a verification check. In this paper, we give the first proof-of-retrievability schemes with full proofs of security against arbitrary adversaries in the strongest model, that of Juels and Kaliski. Our first scheme, built from BLS signatures and secure in the random oracle model, has the shortest query and response of any proof-of-retrievability with public verifiability. Our second scheme, which builds elegantly on pseudorandom functions (PRFs) and is secure in the standard model, has the shortest response of any proof-of-retrievability scheme with private verifiability (but a longer query). Both schemes rely on homomorphic properties to aggregate a proof into one small authenticator value.

/pdf/compact-proofs-of-retrievability-2cuaz82nov.pdf

Compact Proofs of Retrievability

An authenticated encryption scheme is a symmetric encryption scheme whose goal is to provide both privacy and integrity. We consider two possible notions of authenticity for such schemes, namely integrity of plaintexts and integrity of ciphertexts, and relate them (when coupled with IND-CPA) to the standard notions of privacy (IND-CCA,NM-CPA) by presenting implications and separations between all notions considered. We then analyze the security of authenticated encryption schemes designed by “generic composition,” meaning making blackbox use of a given symmetric encryption scheme and a given MAC. Three composition methods are considered, namely Encrypt-and-MAC, MAC-then-encrypt, and Encrypt-then-MAC. For each of these, and for each notion of security, we indicate whether or not the resulting scheme meets the notion in question assuming the given symmetric encryption scheme is secure against chosen-plaintext attack and the given MAC is unforgeable under chosen-message attack. We provide proofs for the cases where the answer is “yes” and counter-examples for the cases where the answer is “no.”

/pdf/authenticated-encryption-relations-among-notions-and-2asso16w07.pdf

Authenticated Encryption: Relations among notions and analysis of the generic composition paradigm.

At some point in the future, how far out we do not exactly know, wireless access to the Internet will outstrip all other forms of access bringing the freedom of mobility to the way we access the we...

ACM SIGCOMM computer communication review

Recent work by Krawczyk [12] and Menezes [16] has highlighted the importance of understanding well the guarantees and limitations of formal security models when using them to prove the security of protocols In this paper we focus on security models for authenticated key exchange (AKE) protocols We observe that there are several classes of attacks on AKE protocols that lie outside the scope of the Canetti-Krawczyk model Some of these additional attacks have already been considered by Krawczyk [12] In an attempt to bring these attacks within the scope of the security model we extend the Canetti-Krawczyk model for AKE security by providing significantly greater powers to the adversary Our contribution is a more compact, integrated, and comprehensive formulation of the security model We then introduce a new AKE protocol called NAXOS and prove that it is secure against these stronger adversaries

/pdf/stronger-security-of-authenticated-key-exchange-1t0j7ztp7s.pdf

Stronger security of authenticated key exchange

An authenticated encryption scheme is a symmetric encryption scheme whose goal is to provide both privacy and integrity. We consider two possible notions of authenticity for such schemes, namely integrity of plaintexts and integrity of ciphertexts, and relate them, when coupled with IND-CPA (indistinguishability under chosen-plaintext attack), to the standard notions of privacy IND-CCA and NM-CPA (indistinguishability under chosen-ciphertext attack and nonmalleability under chosen-plaintext attack) by presenting implications and separations between all notions considered. We then analyze the security of authenticated encryption schemes designed by “generic composition,” meaning making black-box use of a given symmetric encryption scheme and a given MAC. Three composition methods are considered, namely Encrypt-and-MAC, MAC-then-encrypt, and Encrypt-then-MAC. For each of these and for each notion of security, we indicate whether or not the resulting scheme meets the notion in question assuming that the given symmetric encryption scheme is secure against chosen-plaintext attack and the given MAC is unforgeable under chosen-message attack. We provide proofs for the cases where the answer is “yes” and counter-examples for the cases where the answer is “no.”

/pdf/authenticated-encryption-relations-among-notions-and-4s8vvjvgpy.pdf

Authenticated Encryption: Relations among Notions and Analysis of the Generic Composition Paradigm

In this paper we analyse the security of a new key exchange protocol proposed in [3], which is based on mutually learning neural networks. This is a new potential source for public key cryptographic schemes which are not based on number theoretic functions, and have small time and memory complexities. In the first part of the paper we analyse the scheme, explain why the two parties converge to a common key, and why an attacker using a similar neural network is unlikely to converge to the same key. However, in the second part of the paper we show that this key exchange protocol can be broken in three different ways, and thus it is completely insecure.

Analysis of neural cryptography

We demonstrate a system designed to elicit relative relevance judgments from users to rank images with respect to an image query. The system has been deployed and in use publicly for approximately one year. Furthermore, preference data collected from the users has been made available for research purposes. Further details regarding research on this system is available from Bennett et al. [1].

/pdf/picture-this-preferences-for-image-search-3mr76t3dde.pdf

Picture this: preferences for image search

Interactively associating user-defined descriptions with objects. At least two users create descriptions based on provided objects. The users analyze the descriptions to determine whether the users were provided with the same or different objects. If all the users are correct in their determinations, associations between the created descriptions and the corresponding objects are adjusted. In some embodiments, the users interact via a two-player game where the input is obfuscated and the output is optionally obfuscated. For example, the users each provide a search query responsive to receipt of a search intention. If a single search intention was provided and all the users make the correct determination, the search queries are associated with the search intention.

Associating user-defined descriptions with objects

An exemplary method for verifying the integrity of remotely stored data includes providing a key; providing a fingerprint, the fingerprint generated using the key in a keyed cryptographic hash function as applied to data of known integrity; sending the key to a remote storage location that stores a copy of the data of known integrity; receiving a fingerprint from the remote storage location, the fingerprint generated using the key in a keyed cryptographic hash function as applied to the remotely stored copy of the data; and verifying the integrity of the remotely stored copy of the data based at least in part on comparing the provided fingerprint to the received fingerprint. Other exemplary methods, systems, etc., are also disclosed.

Protocol for verifying integrity of remote data

We consider a mix-network as a cryptographic primitive that provides anonymity. A mix-network takes as input a number of ciphertexts and outputs a random shuffle of the corresponding plaintexts. Common applications of mix-nets are electronic voting and anonymous network traffic. In this paper, we present a novel construction of a mix-network, which is based on shuffling ElGamal encryptions. Our scheme is the first mix-net to meet the strongest security requirements: it is robust and secure against chosen ciphertext attacks as well as against active attacks in the Universally Composable model. Our construction allows one to securely execute several mix-net instances concurrently, as well as to run multiple mix-sessions without changing a set of keys. Nevertheless, the scheme is efficient: it requires a linear work (in the number of input messages) per mix-server.

Anton Mityagin

Papers

Analysis of neural cryptography

Picture this: preferences for image search

Associating user-defined descriptions with objects

Protocol for verifying integrity of remote data

Mix-Network with stronger security