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02 May 2024
Arka Rai Choudhuri, Sanjam Garg, Julien Piet, Guru-Vamsi Policharla
In this work we focus on achieving mempool transaction privacy through a new primitive that we term batched-threshold encryption, which is a variant of threshold encryption with strict efficiency requirements to better model the needs of resource constrained environments such as blockchains. Unlike the naive use of threshold encryption, which requires communication proportional to $O(nB)$ to decrypt $B$ transactions with a committee of $n$ parties, our batched-threshold encryption scheme only needs $O(n)$ communication. We additionally discuss pitfalls in prior approaches that use (vanilla) threshold encryption for mempool privacy.
To show that our scheme is concretely efficient, we implement our scheme and find that transactions can be encrypted in under 6 ms, independent of committee size, and the communication required to decrypt an entire batch of $B$ transactions is 80 bytes per party, independent of the number of transactions $B$, making it an attractive choice when communication is very expensive. If deployed on Ethereum, which processes close to 500 transaction per block, it takes close to 2.8 s for each committee member to compute a partial decryption and under 3.5 s to decrypt all transactions for a block in single-threaded mode.
Abdoulaye Ndiaye
Karolin Varner, Wanja Zaeske, Sven Friedrich, Aaron Kaiser, Alice Bowman
Because cryptographic technology can suddenly become obsolete as attacks become more sophisticated, "crypto-agility" -– the ability to swiftly replace ciphers – represents the key challenge to deployment of software like ours. Partitioning is a crucial method for establishing such agility, as it enables the replacement of compromised software without affecting software on other partitions, greatly simplifying the certification process necessary in an avionics environment.
Our performance measurements constitute initial evidence that both the memory and performance characteristics of this approach are suitable for deployment in flight-computers currently in use. Prior to optimisation, performance measurements show a modest memory requirement of under 400 KB of RAM, but employ a more substantial stack usage of just under 200 KB. Our most advanced redundant post-quantum cipher is five times slower than its non-redundant, pre-quantum counterpart.
Mayank Rathee, Yuwen Zhang, Henry Corrigan-Gibbs, Raluca Ada Popa
Amit Deo, Marc Joye, Benoit Libert, Benjamin R. Curtis, Mayeul de Bellabre
In this work, we consider the homomorphic evaluation of pseudorandom functions (PRFs) with a focus on practical lattice-based candidates. In the homomorphic PRF evaluation setting, given a fully homomorphic encryption of the PRF secret key $\vec{s}$, it should be possible to homomorphically compute encryptions of PRF evaluations $\{ \text{PRF}_{\vec{s}}(x_i) \}_{i=1}^M$ for public inputs $\{ x_i\}_{i=1}^M$. We consider this problem for PRF families based on the hardness of the Learning-With-Rounding (LWR) problem introduced by Banerjee, Peikert and Rosen (Eurocrypt '12). We build on the random-oracle variant of a PRF construction suggested by Banerjee et al. and demonstrate that it can be evaluated using only two sequential programmable bootstraps in the TFHE homomorphic encryption scheme. We also describe several modifications of this PRF---which we prove as secure as the original function---that support homomorphic evaluations using only one programmable bootstrap per slot.
Numerical experiments were conducted using practically relevant FHE parameter sets from the TFHE-rs library. Our benchmarks show that a throughput of about $1000$ encrypted pseudorandom bits per second (resp. $900$ encrypted pseudorandom bits per second) can be achieved on an AWS hpc7a.96xlarge machine (resp. on a standard laptop with an Apple M2 chip), on a single thread. The PRF evaluation keys in our experiments have sizes roughly $40\%$ and $60\%$ of a bootstrapping key. Applying our solution to transciphering enables important bandwidth savings, typically trading $64$-bit values for $4$-bit values per transmitted ciphertext.
Xin Wang, Haochen Wang, Haibin Zhang, Sisi Duan
In this paper, we develop BFT protocols from the so-called committee sampling approach that selects a small committee for consensus and conveys the results to all replicas. Such an approach, however, has been focused on the Byzantine agreement (BA) problem (considering replicas only) instead of the BFT problem (in the client-replica model); also, the approach is mainly of theoretical interest only, as concretely, it works for impractically large $n$.
We build an extremely efficient, scalable, and adaptively secure BFT protocol called Pando in partially synchronous environments based on the committee sampling approach. In particular, we devise novel BFT building blocks targeting scalability, including communication-efficient and computation-efficient consistent broadcast and atomic broadcast protocols.
Pando inherits some inherent issues of committee sampling-based protocols: Pando can only achieve near-optimal resilience (i.e., $f<(1/3-\epsilon)n$, where $f$ is the number of faulty replicas and $\epsilon$ is a small constant), and Pando attains safety and liveness only probabilistically. Interestingly, to make $\epsilon$ come close to 0 (near-optimal resilience), $n$ needs to be sufficiently large but not impractically large, e.g., $n>500$---just what we need for scalable BFT.
Our evaluation on Amazon EC2 shows that in contrast to existing protocols, Pando can easily scale to a thousand replicas in the WAN environment, achieving a throughput of 62.57 ktx/sec.
Xinwei Yong, Jiaojiao Wu, Jianfeng Wang
Kelong Cong, Jiayi Kang, Georgio Nicolas, Jeongeun Park
In this paper, we propose two novel non-interactive batched PDTE protocols, BPDTE_RCC and BPDTE_CW, based on two new ciphertext-plaintext comparison algorithms, the improved range cover comparison (RCC) comparator and the constant-weight (CW) piece-wise comparator, respectively. Compared to the current state-of-the-art Level Up (CCS'23), our comparison algorithms are up to $72\times$ faster for batched inputs of 16 bits. Moreover, we introduced a new tree traversal method called Adapted SumPath, to achieve $\mathcal{O}(1)$ complexity of the server's response, whereas Level Up has $\mathcal{O}(2^d)$ for a depth-$d$ tree where the client needs to look up classification values in a table. Overall, our PDTE protocols attain the optimal server-to-client communication complexity and are up to $17\times$ faster than Level Up in batch size 16384.
Albert Garreta, Hayk Hovhanissyan, Aram Jivanyan, Ignacio Manzur, Isaac Villalobos, Michał Zając
Both techniques apply to popular FRI-based proof systems such as ethSTARK, Plonky2/3, RISC Zero, and Boojum.
FE[r]Chain: Enforcing Fairness in Blockchain Data Exchanges Through Verifiable Functional Encryption
Camille Nuoskala, Reyhaneh Rabbaninejad, Tassos Dimitriou, Antonis Michalas
Thijs Veugen, Vincent Dunning, Michiel Marcus, Bart Kamphorst
30 April 2024
Faculty of engineering, Bar-Ilan University, Israel
The position involves performing theoretical research in cryptography, particularly on secure computation over unreliable channels and networks where the adversary controls the communication channels.
The position is offered for 1 year and can be extended by an additional year contingent upon funding and satisfactory performance.
Applicants should ideally have a background in information-theoretic secure computation as well as a general background in cryptography. Knowledge of coding theory and information theory is an advantage. Candidates are expected to be highly motivated and mathematically capable.
Applications should include
(1) a CV including a list of publications,
(2) a short research statement,
(3) names and contact information of 2-3 potential references.
Closing date for applications:
Contact: Applications should be emailed to carmit.hazay@biu.ac.il and ran.gelles@biu.ac.il
Filippo Valsorda, Go cryptography maintainer
I am looking for one or two interns to work on open source cryptography engineering projects, spanning from testing of the Go cryptography standard library, to open source maintenance of industry-spanning projects, to key transparency auditing, to developer tooling.
Detailed examples and application process in the posting.
You’ll be free to choose the project that interests you most amongst those we will discuss, including options that will lead to contributing to popular upstream open source projects, and/or to publishing a technical report on my website or as an ePrint.
- Fully remote. Flexible start date. Twelve weeks (or less).
- Twice a week check-ins, general collaboration via Slack.
- Flexible schedule, core collaboration hours 1500-1900 CET / 0900-1300 ET.
- $5,000 / month ($1,250 / week) regardless of location.
I’m committed to making this a growth and success opportunity in a welcoming, inclusive, and supportive environment.
Apply by May 5th (anywhere on Earth)!
Closing date for applications:
Contact: Filippo Valsorda (see posting)
More information: https://filippo.io/internship
29 April 2024
Tim Beyne, Yu Long Chen
We propose power bounds as an easy-to-use alternative for advantage bounds in the context of indistinguishability with asymmetric cost functions. We show that standard proof techniques such as hybrid arguments and the H-coefficient method can be generalized to the power model, and apply these techniques to the PRP-PRF switching lemma, the Even-Mansour (EM) construction, and the sum-of-permutations (SoP) construction.
As the final and perhaps most useful contribution, we provide two methods to convert single-user power bounds into multi-user power bounds, and investigate their relation to the point-wise proximity method of Hoang and Tessaro (Crypto 2016). These method are applied to obtain tight multi-user power bounds for EM and SoP.
Anaïs Barthoulot, Olivier Blazy, Sébastien Canard
Vincent Rijmen
Davide Carnemolla, Dario Catalano, Mario Di Raimondo, Federico Savasta
Alberto Ibarrondo, Ismet Kerenciler, Hervé Chabanne, Vincent Despiegel, Melek Önen
Xiaohai Dai, Chaozheng Ding, Hai Jin, Julian Loss, Ling Ren
To approach our holy grail, we propose Ipotane. Ipotane achieves performance comparable to partially-synchronous protocols in favorable situations, and attains performance on par with purely asynchronous protocols in unfavorable situations---in both throughput and latency. This is accomplished by our newly introduced primitive Dual-functional Byzantine Agreement (DBA), which packs the functions of (biased) ABA and Validated Asynchronous Byzantine Agreement (VABA). In the context of Ipotane, it promptly detects the optimistic path's failure and, at the same time, generates blocks on the pessimistic path with little extra work. We conduct extensive experiments to demonstrate that Ipotane achieves high throughput and low latency in all situations.
Samuel Lavery
Empirical evidence and statistical testing support the zero-knowledge, completeness, and soundness properties of the Adh proof system. Comparative analysis demonstrates the Adh system's advantages in terms of key and proof sizes over existing post-quantum schemes like Kyber and Dilithium.
This paper represents an early preprint and is a work in progress. The core security arguments and experimental results are present, and formal proofs and additional analysis are provided. We invite feedback and collaboration from the research community to further strengthen the security foundations of the Adh system and explore its potential applications in quantum-resistant cryptography.