Method and system for inter-DLT networks trust enhancement

1. A method for enhancing a level of trust of a first Distributed Ledger Technology (DLT) network using one or more second DLT networks, where the first and the one or more second DLT networks comprise several computing nodes and are independent DLT networks connected by one or more telecommunications networks, the method comprising:

a) Receiving in the first DLT network a request to validate a smart contract, where for validation of the smart contract a trust policy is used;

b) Computing a hash value h(i) which identifies uniquely a current execution of the smart contract correspondent to a function that triggered the trust policy and a result of the function that triggered the trust policy, and storing said hash value h(i) in a database of the first DLT network;

c) Obtaining a hash value h(i−1) of a previous execution of the smart contract;

d) Transmitting from the first DLT network to the one or more second DLT networks, through at least one of the one or more telecommunications networks, a validation instruction including h(i) and a zero-knowledge proof (prf(i)), wherein prf(i)=Proof(Pk, hp(i), diff(i)), where Proof( ) is a pre-established function, Pk is a pre-established random proof key, diff(i)=h(i)−h(i−1) and hp(i)=hash(h(i)∥diff(i));

e) Receiving through at least one of the one or more telecommunications networks, from each of the one or more second DLT networks to which the validation instruction has been sent, a validation result, where the validation result is obtained in each of the one or more second DLT networks by computing: Verify (Vk, hp(i) 2 , prf(i)) where Verify( ) is a pre-established verification function, Vk is a pre-established random verification key, hp(i) 2 =hash(h(i)∥diff(i) 2 )), and diff(i) 2 =h(i)−h(i−1) 2 where h(i−1) 2 is a hash value stored in each respective second DLT network in the previous execution of the validation for the smart contract; and

f) Aborting further execution of the smart contract in the first DLT network, if more negative validation results than a pre-established threshold are received from the one or more second DLT networks.

2. A method according to claim 1 , wherein said hash value h(i)=hash (addr_SC_App, txid, fx(attr), attr, res), wherein addr_SC_App is an address of an application implementing the smart contract; txid is a transaction ID that triggered the trust policy; fx(attr) is the function that triggered the trust policy; attr is an attribute of the function that triggered the trust policy; and res is the result of the function that triggered the trust policy.

3. A method according to claim 1 , wherein a computation of Verify (Vk, hp(i) 2 , prf(i)) is made in all computing nodes of each of the one or more second DLT networks and the validation result received from each of the one or more second DLT networks is positive only if a result of the pre-established verification function is positive in all the computing nodes of said each one or more second DLT networks or if the result of the pre-established verification function is positive in a number of computing nodes of said each one or more second DLT networks higher than a second pre-established threshold.

4. A method according to claim 1 , wherein the smart contract to be validated is for modification of a network ledger.

5. A method according to claim 1 , wherein a communication between the first DLT network and the one or more second DLT networks is made through a governance instance in each computing node of the first DLT network and the one or more second DLT networks, which manage an interconnection logic between DLT networks, wherein each of the governance instance stores information about all other first DLT network and one or more second DLT networks.

6. A method according to claim 5 , where in step d), using stored network information about the second DLT network the governance instance of a computing node of the first DLT network sends the validation instruction to the governance instance of a computing node of each of the one or more second DLT networks through the one or more telecommunication networks.

7. A method according to claim 1 , wherein each computing node of each of the first DLT network and of the one or more second DLT networks has a register with available trust policies in the DLT network to which a computing node belongs and when a network user wants to add a new trust policy to the first DLT network or one of the one or more second DLT networks, at least one computing node in said DLT network checks if the user has enough permissions to add the new trust policy and only if the user has permission, the new trust policy is registered.

8. A method according to claim 1 , wherein each computing node of each of the first DLT network and of the one or more second DLT networks has a register with available DLT networks to be used to enhance the level of trust, and when a network user sends a request to add a new DLT network, at least one computing node of the DLT network where the request is received, sends the request to the other first DLT network and one or more second DLT networks, which verify if the new DLT network is accepted and only if at least a third pre-established threshold of the other first DLT network and one or more second DLT networks accept the new DLT network, the new DLT network is registered in all computing nodes of the first DLT network and the one or more second DLT networks as the new DLT network to be used to enhance the level of trust.

9. A system for enhancing a level of trust of a first Distributed Ledger Technology (DLT) network using one or more second DLT networks, where the first and the one or more second DLT networks are independent DLT networks connected by a telecommunications network, the system comprising the first DLT network and the one or more second DLT networks, the first DLT network comprising at least one computing node comprising a processor configured to:

receive a request to validate a smart contract, where for validation of the smart contract a trust policy is used;

compute a hash value h(i) which identifies uniquely a current execution of the smart contract correspondent to a function that triggered the trust policy and a result of said function, and store said hash value in a database of the first DLT network;

obtain a hash value h(i−1) of the previous execution of the smart contract;

transmit to a computing node of the one or more second DLT networks a validation instruction including h(i) and a zero-knowledge proof (prf(i)), where prf(i)=Proof(Pk, hp(i), diff(i)), where Proof( ) is a pre-established function, Pk is a pre-established random proof key, diff(i)=h(i)−h(i−1) and hp(i)=hash(h(i)∥diff (i));

the one or more second DLT networks comprising:

at least one computing node comprising a processor configured to:

(i) receive the validation instruction from the first DLT network directly or through another computing node of one of the one or more second DLT networks which at least one computing node belongs to; and

(ii) determine a validation result by calculating: Verify (Vk, hp(i) 2 , prf(i)) where Verify( ) is a pre-established verification function, Vk is a pre-established random verification key, hp(i) 2 =hash(h(i)∥diff(i)) 2 , and diff(i) 2 =h(i)−h(i−1) 2 where h(i−1) 2 is a hash value stored in the computing node in the previous execution of the validation for the smart contract;

where further execution of the smart contract in the first DLT network is aborted, if more negative validation results are received from the one or more second DLT networks than a pre-established threshold.

10. A non-transitory digital data storage medium for storing a computer program which comprises instructions causing a computer executing the program to perform the method according to claim 1 .