*15:17* [Pub][ePrint]
A quantum-safe circuit-extension handshake for Tor, by John Schanck and William Whyte and Zhenfei Zhang
We propose a method for integrating NTRUEncrypt into the ntor key exchange protocol as a means of achieving a quantum-safe variant of forward secrecy. The proposal is a minimal change to ntor, essentially consisting of an NTRUEncrypt-based key exchange performed in parallel with the ntor handshake. Performance figures are provided demonstrating that the client bears most of the additional overhead, and that the added load on the router side is acceptable.We make this proposal for two reasons. First, we believe it to be an interesting case study into the practicality of quantum-safe cryptography and into the difficulties one might encounter when transitioning to quantum-safe primitives within real-world protocols and code-bases. Second, we believe that Tor is a strong candidate for an early transition to quantum-safe primitives; users of Tor may be justifiably concerned about adversaries who record traffic in the present and store it for decryption when technology or cryptanalytic techniques improve in the future.

*15:17* [Pub][ePrint]
Automating Fast and Secure Translations from Type-I to Type-III Pairing Schemes, by Joseph A. Akinyele and Christina Garman and Susan Hohenberger
Pairing-based cryptography has exploded over the last decade, as this algebraic setting offers good functionality and efficiency. However, there is a huge security gap between how schemes are usually analyzed in the academic literature and how they are typically implemented. The issue at play is that there exist multiple types of pairings: Type-I called \"symmetric\" is typically how schemes are presented and proven secure in the literature, because it is simpler and the complexity assumptions can be weaker; however, Type-III called \"asymmetric\" is typically the most efficient choice for an implementation in terms of bandwidth and computation time.There are two main complexities when moving from one pairing type to another. First, the change in algebraic setting invalidates the original security proof. Second, there are usually multiple (possibly thousands) of ways to translate from a Type-I to a Type-III scheme, and the \"best\" translation may depend on the application.

Our contribution is the design, development and evaluation of a new software tool, AutoGroup+, that automatically translates from Type-I to Type-III pairings. The output of AutoGroup+ is: (1) \"secure\" provided the input is \"secure\" and (2) optimal based on the user\'s efficiency constraints (excluding software and run-time errors). Prior automation work for pairings was either not guaranteed to be secure or only partially automated and impractically slow. This work addresses the pairing security gap by realizing a fast and secure translation tool.

*15:17* [Pub][ePrint]
Fully Secure Unbounded Revocable Attribute-Based Encryption in Prime Order Bilinear Groups via Subset Difference Method, by Pratish Datta and Ratna Dutta and Sourav Mukhopadhyay
Providing an efficient revocation mechanism for attribute-based encryption (ABE) is ofutmost importance since over time an user\'s credentials may be revealed or expired. All previously

known revocable ABE (RABE) constructions (a) essentially utilize the complete subtree (CS) scheme

for revocation purpose, (b) are bounded in the sense that the size of the public parameters depends

linearly on the size of the attribute universe and logarithmically on the number of users in the

system, and (c) are either selectively secure, which seems unrealistic in a dynamic system such as

RABE, or fully secure but built in a composite order bilinear group setting, which is undesirable from

the point of view of both efficiency and security. This paper presents the first fully secure unbounded

RABE using subset difference (SD) mechanism for revocation which greatly improves the broadcast

efficiency compared to the CS scheme. Our RABE scheme is built on a prime order bilinear group

setting resulting in practical computation cost, and its security depends on the Decisional Linear

assumption.

*15:17* [Pub][ePrint]
Security Analysis of Re-Encryption RPC Mix Nets, by Ralf Kuesters and Tomasz Truderung
Re-Encryption randomized partial checking (RPC) mix nets were introduced by Jakobsson, Juels, and Rivest in 2002 and since then have been employed in prominent modern e-voting systems and in politically binding elections in order to provide verifiable elections in a simple and efficient way. Being one of or even the most used mix nets in practice so far, these mix nets are an interesting and valuable target for rigorous security analysis.In this paper, we carry out the first formal cryptographic analysis of re-encryption RPC mix nets. We show that these mix nets, with fixes recently proposed by Khazaei and Wikstr{\\\"o}m, provide a good level of verifiability, and more precisely, accountability: cheating mix servers, who try to manipulate the election outcome, are caught with high probability. Moreover, we show that all attacks that would break the privacy of voters\' inputs are caught with a probability of at least $1/4$. In many cases, for example, when penalties are severe or reputation can be lost, adversaries might not be willing to take this risk, and hence, would behave in a way that avoids this risk. Now, for such a class of ``risk-avoiding\'\' adversaries, we show that re-encryption RPC mix nets provide a good level of privacy, even if only one mix server is honest.

*15:17* [Pub][ePrint]
Identity-Based Encryption Secure Against Selective Opening Chosen-Ciphertext Attack, by Junzuo Lai and Robert H. Deng and Shengli Liu and Jian Weng and Yunlei Zhao
Security against selective opening attack (SOA) requires that in a multi-user setting, even if an adversary has access to all ciphertexts from users, and adaptively corrupts some fraction of the users by exposing not only their messages but also the random coins, the remaining unopened messages retain their privacy. Recently, Bellare, Waters and Yilek considered SOA-security in the identity-based setting, and presented the first identity-based encryption (IBE) schemes that are proven secure against selective opening chosen plaintext attack (SO-CPA). However, how to achieve SO-CCA security for IBE is still open.In this paper, we introduce a new primitive called extractable IBE, which is a hybrid of one-bit IBE and identity-based key encapsulation mechanism (IB-KEM), and define its IND-ID-CCA security notion. We present a generic construction of SO-CCA secure IBE from an IND-ID-CCA secure extractable IBE with ``One-Sided Public Openability\'\'(1SPO), a collision-resistant hash function and a strengthened cross-authentication code. Finally, we propose two concrete constructions of extractable 1SPO-IBE schemes, resulting in the first simulation-based SO-CCA secure IBE schemes without random oracles.