*08:32*[Event][New] SECITC '13: The 6th International Conference on Security for IT&C

Submission: 29 April 2013

Notification: 28 May 2013

From June 25 to June 26

Location: Bucharest, Romania

More Information: http://www.secitc.eu

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Submission: 29 April 2013

Notification: 28 May 2013

From June 25 to June 26

Location: Bucharest, Romania

More Information: http://www.secitc.eu

Submission: 18 March 2013

Notification: 18 April 2013

From July 22 to July 25

Location: Las Vegas, USA

More Information: http://sam.udmercy.edu/sam13/

2013-01-18

In this paper, we address the problem of formal and automated security verification of WSN transport

protocols that may perform cryptographic operations. The verification of this class of protocols is difficult

because they typically consist of complex behavioral characteristics, such as real-time, probabilistic, and

cryptographic operations. To solve this problem, we propose a

probabilistic timed calculus for cryptographic protocols, and demonstrate how to use this formal language

for proving security or vulnerability of protocols. The main advantage of the proposed language is that it

supports an expressive syntax and semantics, including bisimilarities that supports real-time, probabilistic,

and cryptographic issues at the same time. Hence, it can be used to verify the systems that involve these three

property in a more convenient way. In addition, we propose an automatic verification method, based on the

well-known PAT process analysis toolkit, for this class of protocols.

For demonstration purposes, we apply the proposed manual and automatic proof methods for verifying the security of

DTSN and SDTP, which are two of the recently proposed WSN tranport protocols.

We analyze four recently proposed normal forms for elliptic curves. Though these forms are mathematically appealing and exhibit some cryptographically desirable properties, they nonetheless fall short of cryptographic viability, especially when compared to various types of Edwards Curves. In this paper, we present these forms and demonstrate why they fail to measure up to the standards set by Edwards Curves.

In ACM CCS 2008, Boldyreva et al. proposed an elegant way of achieving an Identity-based Encryption (IBE) with {\\em efficient} revocation, which we call revocable IBE (RIBE). One of the significant benefit of their construction is scalability, where the overhead of the trusted authority is logarithmically increased in the number of users, whereas that in the Boneh-Franklin naive revocation way is linearly increased. All subsequent RIBE schemes follow the Boldyreva et al. security model and syntax. In this paper, we first revisit the Boldyreva et al. security model,

and aim at capturing the exact notion for the security of the naive but non-scalable Boneh-Franklin RIBE scheme. To this end, we consider a realistic threat, which we call {\\em decryption key exposure}. We also show that all prior RIBE constructions except for the Boneh-Franklin one are vulnerable to decryption key exposure. As the second contribution, we revisit approaches to achieve (efficient and adaptively secure) scalable RIBE schemes, and propose a simple RIBE scheme, which is the first scalable RIBE scheme with decryption key exposure resistance, and is more efficient than previous (adaptively secure) scalable RIBE schemes.

In particular, our construction has the shortest ciphertext size and the fastest decryption algorithm even compared with all scalable RIBE schemes without decryption key exposure resistance.

This paper provides the provable-security treatment of path vector routing protocols. We first design a security definition for routing path vector protocols by studying, generalizing, and formalizing numerous known threats. Our model incorporates three major security goals. It is quite strong, yet simple to use. We prove by reduction that S-BGP satisfies two out of the security model\'s three goals, assuming the underlying signature scheme is secure. Under the same assumption, we next show how the protocol can be modified to meet all three security goals simultaneously. We also analyze SoBGP and show that it fails to meet two security goals. Finally, we study security of partial PKI deployment of path vector protocols when not all nodes have public keys. We investigate the possibilities of relaxing the PKI requirement and relying on non-cryptographic physical security of networks that use the protocol in order to achieve possibly weaker, but still well-defined, notions of security. We also present the necessary and sufficient conditions to achieve full security in the partial PKI deployment scenario. We believe our conclusions will prove useful for protocol developers, standards bodies and government agencies.

In the public key cryptosystems, revocation functionality is required when a secret key is corrupted by hacking or the period of a contract expires. In the public key infrastructure setting, numerous solutions have been proposed, and in the Identity Based Encryption (IBE) setting, a recent series of papers proposed revocable IBE schemes. Delegation of key generation is also an important functionality in cryptography from a practical standpoint since it allows reduction of excessive workload for a single key generation authority. Although fficient solutions for either revocation or delegation of key generation in IBE systems have been proposed, an important open problem is efficiently delegating both the key generation and revocation functionalities in IBE systems. Libert and Vergnaud, for instance, left this as an open problem in their CT-RSA 2009 paper. In this paper, we propose the first solution for this problem. We prove the selective-ID security of our proposal under the Decisional Bilinear Diffie-Hellman assumption in the standard model.

The question of security of various efficient key-length

extending constructions for block ciphers in the ideal

cipher model has so far received considerable attention. The

security of triple encryption was investigated in

[Luc98,BR06], longer cascades were considered in [GM09] and

a construction with comparable security as triple encryption

requiring only 2 block cipher calls, denoted 2-XOR-cascade,

was proposed and analyzed in [GT12].

In this paper, we put the above results into perspective by

completing the picture of the investigated landscape in

various ways. We give the following attacks and security

lower bounds for constructions using a block cipher with key

length $k$ and block length $n$:

- For the plain cascade of odd (resp. even) length $l$ we

present a generic attack requiring roughly

$2^{k+\\frac{l-1}{l+1}n}$ (resp. $2^{k+\\frac{l-2}{l}n}$)

queries. This is a generalization of both the well-known

meet-in-the-middle attack on double encryption and the

attack on triple cascade given in [Luc98].

- For the general case of XOR-cascade of odd (resp. even)

length $l$ we prove security up to

$2^{k+\\frac{l-1}{l+1}n}$ (resp. $2^{k+\\frac{l-2}{l}n}$)

queries and also an improved bound $2^{k+\\frac{l-1}{l}n}$

for the special case $l\\in\\{3,4\\}$. This is achieved by

relating the problem to existing results in an independent

line of work on the security of key-alternating ciphers in

the random permutation model.

- Finally, for a natural class of sequential constructions

where block cipher encryptions are interleaved with

key-dependent permutations, we show a generic attack

requiring roughly $2^{k+\\frac{l-1}{l}n}$ queries. Since

XOR-cascades are sequential, this proves tightness of our

above result for XOR-cascades of length $l\\in\\{3,4\\}$ as

well as their optimal security within the class of

sequential constructions.

Aggregate signatures provide bandwidth-saving aggregation of ordinary signatures. We present the first unrestricted instantiation in the standard model, Moreover, our construction yields a multisignature scheme where a single message is signed by a number of signers. Our second result is an application to verifiably encrypted signatures. There, signers encrypt their signature under the public key of a trusted third party and output a proof that the signature is inside. Upon dispute between signer and verifier, the trusted third party is able to recover the signature. These schemes are provably secure in the standard model.

We introduce the notion of rate-limited secure function evaluation (RL-SFE). Loosely speaking, in an RL-SFE protocol participants can monitor and limit the number of distinct inputs (i.e., rate) used by their counterparts in multiple executions of an SFE, in a private and verifiable manner. The need for RL-SFE naturally arises in a variety of scenarios: e.g., it enables service providers to ``meter\'\' their customers\' usage without compromising their privacy, or can be used to prevent oracle attacks against SFE constructions.

We consider three variants of RL-SFE providing different levels of security. As a stepping stone, we also formalize the notion of commit-first SFE (cf-SFE) wherein parties are committed to their inputs before each SFE execution. We provide compilers for transforming any cf-SFE protocol into each of the three RL-SFE variants. Our compilers are accompanied with simulation-based proofs of security in the standard model and show a clear tradeoff between the level of security offered and the overhead required. Moreover, motivated by the fact that in many client-server applications clients do not keep state, we also describe a general approach for transforming the resulting RL-SFE protocols into stateless ones.

As a case study, we take a closer look at the oblivious polynomial evaluation (OPE) protocol of Hazay and Lindell, show that it is commit-first and instantiate efficient rate-limited variants of it.

We utilise a simulated annealing algorithm to find several nonlinear approximations to various S-boxes which can be used to replace the linear approximations in the outer rounds of existing attacks. We propose three variants of a new nonlinear cryptanalytic algorithm which overcomes the main issues that prevented the use of nonlinear approximations in previous research, and we present the statistical frameworks for calculating the complexity of each version. We present new attacks on 11-round Serpent with better data complexity than any other known-plaintext or chosen-plaintext attack, and with the best overall time complexity for a 256-bit key.