Pratik Sarkar
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pratikscrypto.bsky.social
Pratik Sarkar
@pratikscrypto.bsky.social
110 followers 150 following 4 posts
Cryptography, ZK, and MPC Researcher | Currently a Research Scientist at Supra | ex-Cryptography Research Intern at Meta and Visa
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pratikscrypto.bsky.social
We generate instantly verifiable randomness that can be used on-chain without requiring two transactions.
eprint.ing.bot ePrint Updates @eprint.ing.bot · May 21
InstaRand: Instantly Available and Instantly Verifiable On-chain Randomness (Jacob Gorman, Lucjan Hanzlik, Aniket Kate, Pratyay Mukherjee, Pratik Sarkar, Sri AravindaKrishnan Thyagarajan) ia.cr/2025/896
Abstract. Web3 applications, such as on-chain gaming, require unbiased and publicly verifiable randomness that can be obtained quickly and cost-effectively whenever needed. Existing services, such as those based on Verifiable Random Functions (VRF), incur network delays and high fees due to their highly interactive nature. FlexiRand [CCS 2023] addressed these problems by hiding the output of the VRF and using that as a seed to derive many randomnesses locally. These randomnesses are instantly available for usage. However, these randomnesses can not be verified independently (or instantly) without disclosing the seed, leaving scope for malicious actors to cheat. To solve this problem, we introduce a new notion, called instantly-verifiable VRF (iVRF), which enables the generation of many randomnesses from one VRF output seed, such that each of them is verifiable independently - this enables the first solution to cost − effectively generate randomnesses, such that they are instantly available and also independently/instantly verifiable. To instantiate we propose a generic construction called InstaRand - it combines any (possibly distributed) VRF at the server’s end with another VRF at the client’s end to construct an iVRF. Our specific instantiation uses the BLS-based GLOW-DVRF [Euro S&P 2021] at the server’s end and the DDH-based VRF of Goldberg et al. [RFC 2023] at the client’s end. We use the universal composability framework to analyze the security. Moreover, due to its generality, InstaRand can be instantiated with any post-quantum secure VRF to yield a post-quantum secure iVRF. Our experiments demonstrate that our instantiation of InstaRand is highly practical. The client incurs a one − time cost to generate the seed (server’s VRF output) by querying the GLOW-dVRF servers once. Once the seed is set up, the client locally generates the pseudorandom value on demand in 0.18 ms, avoiding the client-server round-trip delay. Each value can be independently verified in 0.22 ms. This yields a 400× improvement in terms of output generation and 20× improvement in verification cost over existing solutions. Image showing part 2 of abstract.
May 21, 2025 at 2:59 PM
pratikscrypto.bsky.social
Dyna-hints got accepted in Crypto Valley Conference'25. See you all at Switzerland!
eprint.ing.bot ePrint Updates @eprint.ing.bot · Apr 11
Dyna-hinTS: Silent Threshold Signatures for Dynamic Committees (Aniket Kate, Pratyay Mukherjee, Samipa Samanta, Pratik Sarkar) ia.cr/2025/631
Abstract. The works of Garg et al. [S&P’24] (aka hinTS) and Das et al. [CCS’23] introduced the notion of silent threshold signatures (STS) - where a set of signers silently perform local computation to generate a public verification key. To sign a message, any set of t signers sign the message non-interactively and these are aggregated into a constant-sized signature. This paradigm avoids performing expensive Distributed Key Generation procedure for each set of signers while keeping the public verification key constant-sized. In this work, we propose the notion of committee-based silent threshold signature (c-STS) scheme. In a c-STS scheme, a set of signers initially perform a one-time setup to generate the verification key, and then a subset of signers are randomly chosen for an epoch to perform the threshold signing while the other signers are not authorized to sign during that epoch. This captures existing systems like Ethereum Altair and Dfinity where only a specific committee is authorized to sign in a designated epoch. The existing STS schemes cannot be extended to the committee setting because the signature verification only attests to the number of signing parties, not which committee they belong to. So, we upgrade hinTS to the committee setting by proposing Dyna-hinTS. It is the first c-STS scheme and it requires a one-time silent setup and generates a one-time public verification key that does not vary with the committee. Assuming a set of 1024 signers (with corrupt 682 signers), hinTS generates an aggregated signature in 1.7s whereas Dyna-hinTS generates it in 0.35s within a committee of 80 signers. This yields a 4.9× improvement over hinTS for signature generation at the cost of increasing signature verification time by 4% over hinTS. Dyna-hinTS supports general access structure, weighted signatures and improves existing multiverse threshold signatures. Image showing part 2 of abstract.
April 11, 2025 at 7:16 AM
Reposted by Pratik Sarkar
aravind16coiner.bsky.social
Happy to announce our paper "VRaaS: Verifiable Randomness as a Service on Blockchains" was accepted into IEEE CSF 2025. Led by @pratikscrypto.bsky.social @aniketkate.bsky.social, and Jacob Gorman from Supra. The paper can be found here eprint.iacr.org/2024/957
VRaaS: Verifiable Randomness as a Service on Blockchains
Web3 applications, such as on-chain games, NFT minting, and leader elections necessitate access to unbiased, unpredictable, and publicly verifiable randomness. Despite its broad use cases and huge dem...
eprint.iacr.org
April 9, 2025 at 11:39 AM
pratikscrypto.bsky.social
New Social Recovery Scheme!
eprint.ing.bot ePrint Updates @eprint.ing.bot · Mar 26
ANARKey: A New Approach to (Socially) Recover Keys (Aniket Kate, Pratyay Mukherjee, Hamza Saleem, Pratik Sarkar, Bhaskar Roberts) ia.cr/2025/551
Abstract. In a social key recovery scheme, users back up their secret keys (typically using Shamir’s secret sharing) with their social connections, known as a set of guardians. This places a heavy burden on the guardians, as they must manage their shares both securely and reliably. Finding and managing such a set of guardians may not be easy, especially when the consequences of losing a key are significant. We take an alternative approach of social recovery within a community, where each member already holds a secret key (with possibly an associated public key) and uses other community members as their guardians forming a mutual dependency among themselves. Potentially, each member acts as a guardian for upto (n−1) other community members. Therefore, in this setting, using standard Shamir’s sharing leads to a linear (O(n)) blow-up in the internal secret storage of the guardian for each key recovery. Our solution avoids this linear blowup in internal secret storage by relying on a novel secret-sharing scheme, leveraging the fact that each member already manages a secret key. In fact, our scheme does not require guardians to store anything beyond their own secret keys. We propose the first formal definition of a social key recovery scheme for general access structures in the community setting. We prove that our scheme is secure against any malicious and adaptive adversary that may corrupt up to t parties. As a main technical tool, we use a new notion of secret sharing, that enables (t+1) out of n sharing of a secret even when the shares are generated independently – we formalize this as bottom-up secret sharing (BUSS), which may be of independent interest. Finally, we provide an implementation benchmarking varying the number of guardians both in a regional, and geo-distributed setting. For instance, for 8 guardians, our backup protocol takes around 146-149 ms in a geo-distributed WAN setting, and 4.9-5.9 ms in the LAN setting; for recovery protocol, the timings are approximately the same for the WAN setting (as network latency dominates), and 1.2-1.4 ms for the LAN setting. Image showing part 2 of abstract. Image showing part 3 of abstract.
March 26, 2025 at 4:16 PM
pratikscrypto.bsky.social
I will be attending Indian Blockchain Week (IBW2024) next week in Bangalore.

If you want to talk about Secure computation, Cryptography, ZK, Blockchain or anything related to privacy I would be happy to meet and discuss.

indiablockchainweek.com
India Blockchain Week 2024 (Dec 2-8) | IBW Conference (Dec 4-5) | Sheraton Grand, Bangalore
Stay tuned for the IBW2024 Conference – Accelerating India's Digital Renaissance. Join us at the Sheraton Grand, Bangalore on December 4-5, 2024. Hosted by Hashed Emergent. Tickets coming soon!
indiablockchainweek.com
November 30, 2024 at 11:52 AM