International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Arnab Roy

Affiliation: University of Bristol, United Kingdom

Publications

Year
Venue
Title
2019
ASIACRYPT
Forkcipher: A New Primitive for Authenticated Encryption of Very Short Messages
Highly efficient encryption and authentication of short messages is an essential requirement for enabling security in constrained scenarios such as the CAN FD in automotive systems (max. message size 64 bytes), massive IoT, critical communication domains of 5G, and Narrowband IoT, to mention a few. In addition, one of the NIST lightweight cryptography project requirements is that AEAD schemes shall be “optimized to be efficient for short messages (e.g., as short as 8 bytes)”.In this work we introduce and formalize a novel primitive in symmetric cryptography called forkcipher. A forkcipher is a keyed primitive expanding a fixed-lenght input to a fixed-length output. We define its security as indistinguishability under a chosen ciphertext attack (for n-bit inputs to 2n-bit outputs). We give a generic construction validation via the new iterate-fork-iterate design paradigm.We then propose $$ {\mathsf {ForkSkinny}} $$ as a concrete forkcipher instance with a public tweak and based on SKINNY: a tweakable lightweight cipher following the TWEAKEY framework. We conduct extensive cryptanalysis of $$ {\mathsf {ForkSkinny}} $$ against classical and structure-specific attacks.We demonstrate the applicability of forkciphers by designing three new provably-secure nonce-based AEAD modes which offer performance and security tradeoffs and are optimized for efficiency of very short messages. Considering a reference block size of 16 bytes, and ignoring possible hardware optimizations, our new AEAD schemes beat the best SKINNY-based AEAD modes. More generally, we show forkciphers are suited for lightweight applications dealing with predominantly short messages, while at the same time allowing handling arbitrary messages sizes.Furthermore, our hardware implementation results show that when we exploit the inherent parallelism of $$ {\mathsf {ForkSkinny}} $$ we achieve the best performance when directly compared with the most efficient mode instantiated with SKINNY.
2019
ASIACRYPT
Shorter QA-NIZK and SPS with Tighter Security
Quasi-adaptive non-interactive zero-knowledge proof (QA-NIZK) systems and structure-preserving signature (SPS) schemes are two powerful tools for constructing practical pairing-based cryptographic schemes. Their efficiency directly affects the efficiency of the derived advanced protocols.We construct more efficient QA-NIZK and SPS schemes with tight security reductions. Our QA-NIZK scheme is the first one that achieves both tight simulation soundness and constant proof size (in terms of number of group elements) at the same time, while the recent scheme from Abe et al. (ASIACRYPT 2018) achieved tight security with proof size linearly depending on the size of the language and the witness. Assuming the hardness of the Symmetric eXternal Diffie-Hellman (SXDH) problem, our scheme contains only 14 elements in the proof and remains independent of the size of the language and the witness. Moreover, our scheme has tighter simulation soundness than the previous schemes.Technically, we refine and extend a partitioning technique from a recent SPS scheme (Gay et al., EUROCRYPT 2018). Furthermore, we improve the efficiency of the tightly secure SPS schemes by using a relaxation of NIZK proof system for OR languages, called designated-prover NIZK system. Under the SXDH assumption, our SPS scheme contains 11 group elements in the signature, which is shortest among the tight schemes and is the same as an early non-tight scheme (Abe et al., ASIACRYPT 2012). Compared to the shortest known non-tight scheme (Jutla and Roy, PKC 2017), our scheme achieves tight security at the cost of 5 additional elements.All the schemes in this paper are proven secure based on the Matrix Diffie-Hellman assumptions (Escala et al., CRYPTO 2013). These are a class of assumptions which include the well-known SXDH and DLIN assumptions and provide clean algebraic insights to our constructions. To the best of our knowledge, our schemes achieve the best efficiency among schemes with the same functionality and security properties. This naturally leads to improvement of the efficiency of cryptosystems based on simulation-sound QA-NIZK and SPS.
2016
ASIACRYPT
2015
EPRINT
2014
CHES
2014
FSE
2013
CHES
2013
FSE
2011
FSE

Program Committees

PKC 2020
FSE 2019