OUR MISSION
The Blockchain & Platform chair combines academic excellence with business & tech leadership to foster blockchain innovation.
PUBLICATIONS
Reversible and Composable Financial Contracts (extended abstract)
It is widely believed that financial markets cannot be liquid without centralised processes to manage counterparty risk. We propose an alternative method for liquidity based on reversible and composable contracts run atop a blockchain. Novel instruments for zero-collateral intermediation can be defined.
Fundamental Pricing of Utility Tokens
We propose a framework for the fundamental valuation of utility tokens. Our model endogenizes the velocity of circulation of tokens and yields a pricing formula that is fully microfounded. According to our model, tokens are valuable because they have to be immediately accessible when the services are needed, a requirement that is reminiscent of the cash-in-advance constraint. The equilibrium price paths of successful projects go through two successive phases: A speculative phase where marginal holders are investors that do not intend to use the services and, later on, a user phase where all tokens are held by clients. Calibrating the model, we find that it helps rationalizing the extreme volatility and significant valuation of tokens early on during the adoption stage.
2-Step Multi-Client Quadratic Functional Encryption from Decentralized Function-Hiding Inner-Product
In this paper, we present a multi-client quadratic functional encryption (MCQFE) scheme from function-hiding inner-product (FHIP). The main challenge in such construction is that all the clients require the access to the master secret key of
the underlying FHIP scheme, which clearly breaches the security.
To overcome this challenge, we present an efficient decentralized version of FHIP scheme of Lin (Crypto 16). This leads to a 2-step MCQFE (2-MCQFE) scheme. In a 2-step MCQFE scheme, the encryption phase is a (non-interactive) protocol among clients and a set of honest-but-curious authorities. More precisely, clients are the owner of messages and the master secret-key of the underlying FHIP is shared among authorities. In the first step, the client publishes a pre-ciphertext pct associated with its message. Then in the second step, each authority generates its share ct_i extracted from the pre-ciphertext. The public aggregation of these shares ct_i will generate the target ciphertext ct which then would be applied on the functional key sk_F to compute the quadratic functionality. The security model is strong enough to consider no trust among clients and authorities, and also the revelation of some secret keys (of clients or authorities) through corruptions. We instantiate our 2-MCQFE scheme and prove its security in the random-oracle model based on the SXDH assumption. Moreover, we show that its security holds as long as at least one of the authorities is not corrupted.
the underlying FHIP scheme, which clearly breaches the security.
To overcome this challenge, we present an efficient decentralized version of FHIP scheme of Lin (Crypto 16). This leads to a 2-step MCQFE (2-MCQFE) scheme. In a 2-step MCQFE scheme, the encryption phase is a (non-interactive) protocol among clients and a set of honest-but-curious authorities. More precisely, clients are the owner of messages and the master secret-key of the underlying FHIP is shared among authorities. In the first step, the client publishes a pre-ciphertext pct associated with its message. Then in the second step, each authority generates its share ct_i extracted from the pre-ciphertext. The public aggregation of these shares ct_i will generate the target ciphertext ct which then would be applied on the functional key sk_F to compute the quadratic functionality. The security model is strong enough to consider no trust among clients and authorities, and also the revelation of some secret keys (of clients or authorities) through corruptions. We instantiate our 2-MCQFE scheme and prove its security in the random-oracle model based on the SXDH assumption. Moreover, we show that its security holds as long as at least one of the authorities is not corrupted.
No upcoming events.
See past events.EDUCATION
We provide a series of courses at the Ecole Polytechnique for students and professionals that wish to foster their understanding of DLT and blockchains.
TEAM
The Blockchain & Platform chair is directed by Daniel Augot and Julien Prat. It is composed of researchers and Ph.D. students at the Ecole Poytechnique as well as of associate researchers dedicated to these four areas of expertise :
Cryptography
Distributed Algorithms
Formal proof
