## CryptoDB

### Dawu Gu

#### Publications

Year
Venue
Title
2021
CRYPTO
Double-block Hash-then-Sum (\textsf{DbHtS}) MACs are a class of MACs that aim for achieving beyond-birthday-bound security, including \textsf{SUM-ECBC}, \textsf{PMAC\_Plus}, \textsf{3kf9} and \textsf{LightMAC\_Plus}. Recently Datta et al. (FSE'19), and then Kim et al. (Eurocrypt'20) prove that \textsf{DbHtS} constructions are secure beyond the birthday bound in the single-user setting. However, by a generic reduction, their results degrade to (or even worse than) the birthday bound in the multi-user setting. In this work, we revisit the security of \textsf{DbHtS} MACs in the multi-user setting. We propose a generic framework to prove beyond-birthday-bound security for \textsf{DbHtS} constructions. We demonstrate the usability of this framework with applications to key-reduced variants of \textsf{DbHtS} MACs, including \textsf{2k-SUM-ECBC}, \textsf{2k-PMAC\_Plus} and \textsf{2k-LightMAC\_Plus}. Our results show that the security of these constructions will not degrade as the number of users grows. On the other hand, our results also indicate that these constructions are secure beyond the birthday bound in both single-user and multi-user setting without additional domain separation, which is used in the prior work to simplify the analysis. Moreover, we find a critical flaw in \textsf{2kf9}, which is proved to be secure beyond the birthday bound by Datta et al. (FSE'19). We can successfully forge a tag with probability 1 without making any queries. We go further to show attacks with birthday-bound complexity on several variants of \textsf{2kf9}.
2021
TCHES
With the renaissance of deep learning, the side-channel community also notices the potential of this technology, which is highly related to the profiling attacks in the side-channel context. Many papers have recently investigated the abilities of deep learning in profiling traces. Some of them also aim at the countermeasures (e.g., masking) simultaneously. Nevertheless, so far, all of these papers work with an (implicit) assumption that the number of time samples in raw traces can be reduced before the profiling, i.e., the position of points of interest (PoIs) can be manually located. This is arguably the most challenging part of a practical black-box analysis targeting an implementation protected by masking. Therefore, we argue that to fully utilize the potential of deep learning and get rid of any manual intervention, the end-to-end profiling directly mapping raw traces to target intermediate values is demanded.In this paper, we propose a neural network architecture that consists of encoders, attention mechanisms and a classifier, to conduct the end-to-end profiling. The networks built by our architecture could directly classify the traces that contain a large number of time samples (i.e., raw traces without manual feature extraction) while whose underlying implementation is protected by masking. We validate our networks on several public datasets, i.e., DPA contest v4 and ASCAD, where over 100,000 time samples are directly used in profiling. To our best knowledge, we are the first that successfully carry out end-to-end profiling attacks. The results on the datasets indicate that our networks could get rid of the tricky manual feature extraction. Moreover, our networks perform even systematically better (w.r.t. the number of traces in attacks) than those trained on the reduced traces. These validations imply our approach is not only a first but also a concrete step towards end-to-end profiling attacks in the side-channel context.
2021
TCHES
Deep learning (DL)-based techniques have recently proven to be very successful when applied to profiled side-channel attacks (SCA). In a real-world profiled SCA scenario, attackers gain knowledge about the target device by getting access to a similar device prior to the attack. However, most state-of-the-art literature performs only proof-of-concept attacks, where the traces intended for profiling and attacking are acquired consecutively on the same fully-controlled device. This paper reminds that even a small discrepancy between the profiling and attack traces (regarded as domain discrepancy) can cause a successful single-device attack to completely fail. To address the issue of domain discrepancy, we propose a Cross-Device Profiled Attack (CDPA), which introduces an additional fine-tuning phase after establishing a pretrained model. The fine-tuning phase is designed to adjust the pre-trained network, such that it can learn a hidden representation that is not only discriminative but also domain-invariant. In order to obtain domain-invariance, we adopt a maximum mean discrepancy (MMD) loss as a constraint term of the classic cross-entropy loss function. We show that the MMD loss can be easily calculated and embedded in a standard convolutional neural network. We evaluate our strategy on both publicly available datasets and multiple devices (eight Atmel XMEGA 8-bit microcontrollers and three SAKURA-G evaluation boards). The results demonstrate that CDPA can improve the performance of the classic DL-based SCA by orders of magnitude, which significantly eliminates the impact of domain discrepancy caused by different devices.
2021
ASIACRYPT
For Key Encapsulation Mechanism (KEM) deployed in a multi-user setting, an adversary may corrupt some users to learn their secret keys, and obtain some encapsulated keys due to careless key managements of users. To resist such attacks, we formalize Enhanced security against Chosen Plaintext/Ciphertext Attack (ECPA/ECCA), which ask the pseudorandomness of unrevealed encapsulated keys under uncorrupted users. This enhanced security for KEM serves well for the security of a class of Authenticated Key Exchange protocols built from KEM. In this paper, we study the achievability of tight ECPA and ECCA security for KEM in the multi-user setting, and present an impossibility result and an optimal security loss factor that can be obtained. The existing meta-reduction technique due to Bader et al. (EUROCRYPT 2016) rules out some KEMs, but many well-known KEMs, e.g., Cramer-Shoup KEM (SIAM J. Comput. 2003), Kurosawa-Desmedt KEM (CRYPTO 2004), run out. To solve this problem, we develop a new technique tool named rank of KEM and a new secret key partitioning strategy for meta-reduction. With this new tool and new strategy, we prove that KEM schemes with polynomially-bounded ranks have no tight ECPA and ECCA security from non-interactive complexity assumptions, and the security loss is at least linear in the number n of users. This impossibility result covers lots of well-known KEMs, including the Cramer-Shoup KEM, Kurosawa-Desmedt KEM and many others. Moreover, we show that the linear security loss is optimal by presenting concrete KEMs with security loss Θ(n). This is justified by a non-trivial security reduction with linear loss factor from ECPA/ECCA security to the traditional multi-challenge CPA/CCA security.
2020
TCHES
Persistence fault analysis (PFA) is a novel fault analysis technique proposed in CHES 2018 and demonstrated with rowhammer-based fault injections. However, whether such analysis can be applied to traditional fault attack scenario, together with its difficulty in practice, has not been carefully investigated. For the first time, a persistent fault attack is conducted on an unprotected AES implemented on ATmega163L microcontroller in this paper. Several critical challenges are solved with our new improvements, including (1) how to decide whether the fault is injected in SBox; (2) how to use the maximum likelihood estimation to pursue the minimum number of ciphertexts; (3) how to utilize the unknown fault in SBox to extract the key. Our experiments show that: to break AES with physical laser injections despite all these challenges, the minimum and average number of required ciphertexts are 926 and 1641, respectively. It is about 38% and 28% reductions of the ciphertexts required in comparison to 1493 and 2273 in previous work where both fault value and location have to be known. Furthermore, our analysis is extended to the PRESENT cipher. By applying the persistent fault analysis to the penultimate round, the full PRESENT key of 80 bits can be recovered. Eventually, an experimental validation is performed to confirm the accuracy of our attack with more insights. This paper solves the challenges in most aspects of practice and also demonstrates the feasibility and universality of PFA on SPN block ciphers.
2020
PKC
We revisit the method of designing public-key puncturable encryption schemes and present a generic conversion by leveraging the techniques of distributed key-distribution and revocable encryption. In particular, we first introduce a refined version of identity-based revocable encryption, named key-homomorphic identity-based revocable key encapsulation mechanism with extended correctness . Then, we propose a generic construction of puncturable key encapsulation mechanism from the former by merging the idea of distributed key-distribution. Compared to the state-of-the-art, our generic construction supports unbounded number of punctures and multiple tags per message, thus achieving more fine-grained revocation of decryption capability. Further, it does not rely on random oracles , not suffer from non-negligible correctness error, and results in a variety of efficient schemes with distinct features. More precisely, we obtain the first scheme with very compact ciphertexts in the standard model, and the first scheme with support for both unbounded size of tags per ciphertext and unbounded punctures as well as constant-time puncture operation. Moreover, we get a comparable scheme proven secure under the standard DBDH assumption, which enjoys both faster encryption and decryption than previous works based on the same assumption, especially when the number of tags associated with the ciphertext is large.
2020
ASIACRYPT
We propose a generic construction of 2-pass authenticated key exchange (AKE) scheme with explicit authentication from key encapsulation mechanism (KEM) and signature (SIG) schemes. We improve the security model due to Gjosteen and Jager [Crypto2018] to a stronger one. In the strong model, if a replayed message is accepted by some user, the authentication of AKE is broken. We define a new security notion named ''IND-mCPA with adaptive reveals'' for KEM. When the underlying KEM has such a security and SIG has unforgeability with adaptive corruptions, our construction of AKE equipped with counters as states is secure in the strong model, and stateless AKE without counter is secure in the traditional model. We also present a KEM possessing tight ''IND-mCPA security with adaptive reveals'' from the Computation Diffie-Hellman assumption in the random oracle model. When the generic construction of AKE is instantiated with the KEM and the available SIG by Gjosteen and Jager [Crypto2018], we obtain the first practical 2-pass AKE with tight security and explicit authentication. In addition, the integration of the tightly IND-mCCA secure KEM (derived from PKE by Han et al. [Crypto2019]) and the tightly secure SIG by Bader et al. [TCC2015] results in the first tightly secure 2-pass AKE with explicit authentication in the standard model.
2019
PKC
Robustly reusable Fuzzy Extractor (rrFE) considers reusability and robustness simultaneously. We present two approaches to the generic construction of rrFE. Both of approaches make use of a secure sketch and universal hash functions. The first approach also employs a special pseudo-random function (PRF), namely unique-input key-shift (ui-ks) secure PRF, and the second uses a key-shift secure auxiliary-input authenticated encryption (AIAE). The ui-ks security of PRF (resp. key-shift security of AIAE), together with the homomorphic properties of secure sketch and universal hash function, guarantees the reusability and robustness of rrFE. Meanwhile, we show two instantiations of the two approaches respectively. The first instantiation results in the first rrFE from the LWE assumption, while the second instantiation results in the first rrFE from the DDH assumption over non-pairing groups.
2019
CRYPTO
We propose the concept of quasi-adaptive hash proof system (QAHPS), where the projection key is allowed to depend on the specific language for which hash values are computed. We formalize leakage-resilient(LR)-ardency for QAHPS by defining two statistical properties, including LR-$\langle \mathscr {L}_0, \mathscr {L}_1 \rangle$-universal and LR-$\langle \mathscr {L}_0, \mathscr {L}_1 \rangle$-key-switching.We provide a generic approach to tightly leakage-resilient CCA (LR-CCA) secure public-key encryption (PKE) from LR-ardent QAHPS. Our approach is reminiscent of the seminal work of Cramer and Shoup (Eurocrypt’02), and employ three QAHPS schemes, one for generating a uniform string to hide the plaintext, and the other two for proving the well-formedness of the ciphertext. The LR-ardency of QAHPS makes possible the tight LR-CCA security. We give instantiations based on the standard k-Linear (k-LIN) assumptions over asymmetric and symmetric pairing groups, respectively, and obtain fully compact PKE with tight LR-CCA security. The security loss is ${{O}}(\log {Q_{{e}}})$ where ${Q_{{e}}}$ denotes the number of encryption queries. Specifically, our tightly LR-CCA secure PKE instantiation from SXDH has only 4 group elements in the public key and 7 group elements in the ciphertext, thus is the most efficient one.
2018
PKC
Selective opening security (SO security) is desirable for public key encryption (PKE) in a multi-user setting. In a selective opening attack, an adversary receives a number of ciphertexts for possibly correlated messages, then it opens a subset of them and gets the corresponding messages together with the randomnesses used in the encryptions. SO security aims at providing security for the unopened ciphertexts. Among the existing simulation-based, selective opening, chosen ciphertext secure (SIM-SO-CCA secure) PKEs, only one (Libert et al. Crypto’17) enjoys tight security, which is reduced to the Non-Uniform LWE assumption. However, their public key and ciphertext are not compact.In this work, we focus on constructing PKE with tight SIM-SO-CCA security based on standard assumptions. We formalize security notions needed for key encapsulation mechanism (KEM) and show how to transform these securities into SIM-SO-CCA security of PKE through a tight security reduction, while the construction of PKE from KEM follows the general framework proposed by Liu and Paterson (PKC’15). We present two KEM constructions with tight securities based on the Matrix Decision Diffie-Hellman assumption. These KEMs in turn lead to two tightly SIM-SO-CCA secure PKE schemes. One of them enjoys not only tight security but also compact public key.
2017
CRYPTO
2016
CHES
2016
ASIACRYPT
2015
TCC
2015
CRYPTO
2015
CHES
2014
CHES
2012
FSE

Asiacrypt 2018
Asiacrypt 2015