International Association for Cryptologic Research

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2015-02-26
13:17 [Pub][ePrint]

We construct an identity-based encryption (IBE) scheme that is tightly secure in a very strong sense. Specifically, we consider a setting with many instances of the scheme and many encryptions per instance. In this setting, we reduce the security of our scheme to a variant of a simple assumption used for a similar purpose by Chen and Wee (Crypto 2013). The security loss of our reduction is O(k) (where k is the security parameter). Our scheme is the first IBE scheme to achieve this strong flavor of tightness under a simple assumption.

Technically, our scheme is a variation of the IBE scheme by Chen and Wee. However, in order to \"lift\" their results to the multi-instance, multi-ciphertext case, we need to develop new ideas. In particular, while we build on (and extend) their high-level proof strategy, we deviate significantly in the low-level proof steps.

13:17 [Pub][ePrint]

Designers of secure hardware are required to harden their implementations against physical threats, such as power analysis attacks. In particular, cryptographic hardware circuits are required to decorrelate their current consumption from the information inferred by processing (secret) data. A common technique to achieve this goal is the use of special logic styles that aim at equalizing the current consumption at each single processing step. However, since all hiding techniques like Dual-Rail Precharge (DRP) were originally developed for ASICs, the deployment of such countermeasures on FPGA devices with fixed and predefined logic structure poses a particular challenge.

In this work, we propose and practically evaluate a new DRP scheme (GliFreD) that has been exclusively designed for FPGA platforms. GliFreD overcomes the well-known early propagation issue, prevents glitches, uses an isolated dual-rail concept, and mitigates imbalanced routings. With all these features, GliFreD significantly exceeds the level of physical security achieved by any previously reported, related countermeasures for FPGAs.

13:17 [Pub][ePrint]

We define the new notion of a multilinear pseudorandom function (PRF), and give a construction with a proof of security assuming the hardness of the decisional Diffie-Hellman problem. A direct application of our construction yields (non-multilinear) PRFs with aggregate security from the same assumption, resolving an open question of Cohen, Goldwasser, and Vaikuntanathan. Additionally, multilinear PRFs give a new way of viewing existing algebraic PRF constructions: our main theorem implies they too satisfy aggregate security.

13:17 [Pub][ePrint]

We construct trapdoor permutations based on (sub-exponential) indistinguishability obfuscation and one-way functions, thereby providing the first candidate that is not based on the hardness of factoring.

Our construction shows that even highly structured primitives, such as trapdoor permutations, can be potentially based on hardness assumptions with noisy structures such as those used in candidate constructions of indistinguishability obfuscation. It also suggest a possible way to construct trapdoor permutations that resist quantum attacks, and that their hardness may be based on problems outside the complexity class SZK - indeed, while factoring-based candidates do not possess such security, future constructions of indistinguishability obfuscation might.

As a corollary, we eliminate the need to assume trapdoor permutations and injective one-way function in many recent constructions based on indistinguishability obfuscation.

13:17 [Pub][ePrint]

In this paper we present adaptive key recovery attacks on NTRU-based somewhat homomorphic encryption schemes. Among such schemes, we study the proposal by Bos et al [BLLN13] in 2013. Given access to a decryption oracle, the attack allows us to compute the private key for all parameter choices. Such attacks show that one must be very careful about the use of homomorphic encryption in practice. The existence of a key recovery attack means that the scheme is not CCA1-secure. Indeed, almost every somewhat homomorphic construction proposed till now in the literature is vulnerable to an attack of this type. Hence our result adds to a body of literature that shows that building CCA1-secure homomorphic schemes is not trivial.

13:17 [Pub][ePrint]

A self-bilinear map is a bilinear map where the domain and target groups are identical. In this paper, we introduce a self-bilinear map with auxiliary information which is a weaker variant of a self-bilinear map, construct it based on indistinguishability obfuscation and prove that a useful hardness assumption holds with respect to our construction under the factoring assumption. From our construction, we obtain a multilinear map with interesting properties: the level of multilinearity is not bounded in the setup phase, and representations of group elements are compact, i.e., their size is independent of the level of multilinearity. This is the first construction of a multilinear map with these properties. Note, however, that to evaluate the multilinear map, auxiliary information is required. As applications of our multilinear map, we construct multiparty non-interactive key-exchange and distributed broadcast encryption schemes where the maximum number of users is not fixed in the setup phase. Besides direct applications of our self-bilinear map, we show that our technique can also be used for constructing somewhat homomorphic encryption based on indistinguishability obfuscation and the Phi-hiding assumption.

13:17 [Pub][ePrint]

Non-malleable codes, introduced by Dziembowski, Pietrzak, and Wichs (ICS \'10), provide the guarantee that if a codeword $c$ of a message $m$, is modified by a tampering function $f$ to $c\'$, then $c\'$ either decodes to $m$ or to something unrelated\" to $m$. It is known that non-malleable codes cannot exist for the class of all tampering functions and hence a lot of work has focused on explicitly constructing such codes against a large and natural class of tampering functions. One such popular, but restricted, class is the so-called \\emph{split-state} model in which the tampering function operates on different parts of the codeword \\emph{independently}.

In this work, we remove the above restriction by considering a stronger adversarial model that we call the {\\em block-wise tampering} model. In this model, the adversary can tamper every block of the codeword, with the only restriction being that he can tamper every block at most once. As an example, if a codeword $c = (c_1,c_2)$, then the first tampering function $f_1$ could produce a tampered part $c_1\'=f_1(c_1)$ and the second tampering function $f_2$ could produce $c_2\' = f_2(c_1,c_2)$ which can depend on {\\em both} $c_2$ and $c_1$. An example is when the blocks are being sent one by one and the adversary must temper and send the first block before the second block comes along.

- Surprisingly, defining non-malleability in the block-wise tampering model is challenging. Our first contribution is that of providing a relaxed, yet meaningful definition of non-malleability for this model. Unfortunately, we show, that even this notion is impossible to achieve in the information-theoretic setting (i.e., when the tampering functions can be unbounded) and we must turn our attention towards computationally bounded adversaries.

- Next, we provide an interesting connection between block-wise non-malleable codes and non-malleable commitments. We show that any block-wise non-malleable code can be converted into a non-malleable (wrt opening) commitment. In the other direction, we show that any non-interactive non-malleable (wrt opening) commitment can be used to construct a block-wise non-malleable code (with $2$ blocks).

- While the above transformation gives us a construction of a block-wise non-malleable code, it is based on the highly non-standard assumption of adaptive one-way functions (which can only be realized based on assumptions such as Oracle DDH). As our main result, we show, how to construct a block-wise non-malleable code from any sub-exponentially hard one-way permutations. Our techniques, quite surprisingly, also give rise to a non-malleable commitment scheme (secure against so-called synchronizing adversaries), in which {\\em only} the committer sends messages. We believe this result to be of independent interest.

2015-02-25
17:15 [Job][New]

The positions is funded by the German Research Foundation (DFG) in the project WSNSec (Wireless Sensor Network Security), being a collaboration with Universtiy of Erlangen-Nuremberg.

========

This position ocuses on the theoretical aspects of WSNSec:

- Formalization of attacker models and security goals

- Cryptanalysis of existing cryptographic protocols

- Development of provably secure cryptographic protocols

========

The candidate should have the following qualifications:

• Master degree (or an equivalent degree) in Mathematics, Computer Science or a related discipline

• Experience in cryptography

• Knowledge in the modeling and formal analysis of cryptographic protocols is helpful, but not required

2015-02-24
15:34 [Event][New]

Submission: 24 April 2015
From January 1 to September 11

10:18 [Job][Update]

Postdoc Positions in Cloud-Computing and Storage Security

The cloud storage and cloud solutions security research teams at IBM Research - Zurich are looking for outstanding researchers to strengthen their activities covering security mechanisms for storage systems and cloud computing. Topics include cryptographic schemes addressing privacy and authenticity, software-defined storage systems, and distributed secure protocols.

The successful candidate will hold a PhD in computer science or a related field, with an excellent record of publications and other accomplishments in the field. A good understanding of cryptographic techniques and a strong background in storage systems, file systems, databases, distributed systems and operating systems is beneficial. Candidates must have a strong desire and proven ability to conduct research independently, invent new ideas, implement them in real systems, and publish the results of their work.

The highly motivated, creative individual will join a multi-disciplinary research team to design and implement advanced mechanisms for protecting cloud computing and storage systems.

IBM is committed to diversity at the workplace. With us, you will find an open, multicultural environment. Excellent, flexible working arrangements enable both women and men to strike the desired balance between their professional development and their personal lives.

There is no specific closing date, even though the form here asks for a date.

To apply, please send your CV including contact information for two references by email to: cloudsec (at) zurich.ibm.com

IBM Research - Zurich

http://www.research.ibm.com/labs/zurich/

07:00 [Job][New]

Designed and developed solutions that will allow for seamless multimedia service provisioning and transparently and securely using heterogeneous network technologies.

- Researched for various cryptographic algorithms.

- Recommended a combination of AES and RSA algorithms for encrypted data transmission between chat client peers of a secure chat communication over a messenger.

- Designed and implemented the cryptographic algorithm and the messenger prototype using Java platform.

- Made use of Java for developing the messenger GUI, event handling in GUI through implementing Interfaces, establishing connection between server and client.