Verifying integrity of data stored in a consortium blockchain using a public sidechain

1. A computer-implemented method, comprising:

storing a data item in a consortium blockchain maintained by a consortium blockchain network;

generating a first data digest based on the stored data item;

sending a copy of the first data digest to each of a plurality of verification nodes so that each verification node cryptographically signs the first data digest and stores a corresponding copy of a first signed first data digest in a public blockchain maintained by a public blockchain network;

receiving a request to retrieve the stored data item;

in response to receiving the request, retrieving the requested data item from the consortium blockchain;

generating a second data digest based on the retrieved data item;

sending a copy of the second data digest to each of the plurality of verification nodes so that each verification node cryptographically signs the second data digest and returns a corresponding copy of a second signed second data digest;

receiving the second signed second data digests from the plurality of verification nodes;

retrieving the first signed first data digests from the public blockchain;

determining that the first signed first data digests match the second signed second data digests; and

in response to determining that the first signed digests match the second signed digests, sending a response to the request to retrieve stored data item, the response indicating that the stored data item has not changed since it was stored.

2. The computer-implemented method of claim 1 , wherein the plurality of verification nodes are computing devices participating in the public blockchain network.

3. The computer-implemented method of claim 1 , further comprising storing a smart contract in the public blockchain, wherein the smart contract is configured to provide a monetary reward to the verification nodes in response to receiving the requested signed second data digests from the verification nodes.

4. The computer-implemented method of claim 1 , wherein generating the first data digest includes calculating a hash of the stored data item.

5. The computer-implemented method of claim 1 , wherein each verification node is configured to cryptographically sign the first data digest using a private key associated with that verification node.

6. The computer-implemented method of claim 1 , wherein sending the first data digest to the plurality of verification nodes includes broadcasting the first data digest to the public blockchain network.

7. The computer-implemented method of claim 1 , wherein retrieving the first signed first data digests from the public blockchain includes identifying the first signed first data digests based on an identifier associated with the stored data item and stored in the public blockchain.

8. A non-transitory computer-readable storage medium storing one or more instructions executable by a computer system to perform operations comprising:

storing a data item in a consortium blockchain maintained by a consortium blockchain network;

generating a first data digest based on the stored data item;

sending a copy of the first data digest to each of a plurality of verification nodes so that each verification node cryptographically signs the first data digest and stores a corresponding copy of a first signed first data digest in a public blockchain maintained by a public blockchain network;

receiving a request to retrieve the stored data item;

in response to receive the request, retrieving the requested data item from the consortium blockchain;

generating a second data digest based on the retrieved data item;

sending a copy of the second data digest to each of the plurality of verification nodes so that each verification node cryptographically signs the second data digest and returns a corresponding copy of a second signed second data digest;

receiving the second signed second data digests from the plurality of verification nodes;

retrieving the first signed first data digests from the public blockchain;

determining that the first signed first data digests match the second signed second data digests; and

in response to determining that the first signed digests match the second signed digests, sending a response to the request to retrieve stored data item, the response indicating that the stored data item has not changed since it was stored.

9. The non-transitory computer-readable storage medium of claim 8 , wherein the plurality of verification nodes are computing devices participating in the public blockchain network.

10. The non-transitory computer-readable storage medium of claim 8 , wherein the operations comprise:

store a smart contract in the public blockchain, wherein the smart contract is configured to provide a monetary reward to the verification nodes in response to receiving the requested signed second data digests from the verification nodes.

11. The non-transitory computer-readable storage medium of claim 8 , wherein generating the first data digest includes calculating a hash of the stored data item.

12. The non-transitory computer-readable storage medium of claim 8 , wherein each verification node is configured to cryptographically sign the first data digest using a private key associated with that verification node.

13. The non-transitory computer-readable storage medium of claim 8 , wherein sending the first data digest to the plurality of verification nodes includes broadcasting the first data digest to the public blockchain network.

14. The non-transitory computer-readable storage medium of claim 8 , wherein retrieving the first signed first data digests from the public blockchain includes identifying the first signed first data digests based on an identifier associated with the stored data item and stored in the public blockchain.

15. A system, comprising:

one or more computers; and

one or more computer memory devices interoperably coupled with the one or more computers and having tangible, non-transitory, machine-readable media storing one or more instructions that, when executed by the one or more computers, perform one or more operations comprising:

storing a data item in a consortium blockchain maintained by a consortium blockchain network;

generating a first data digest based on the stored data item;

sending a copy of the first data digest to each of a plurality of verification nodes so that each verification node cryptographically signs the first data digest and stores a corresponding copy of a first signed first data digest in a public blockchain maintained by a public blockchain network;

receiving a request to retrieve the stored data item;

in response to receiving the request, retrieving the requested data item from the consortium blockchain;

generating a second data digest based on the retrieved data item;

sending a copy of the second data digest to each of the plurality of verification nodes so that each verification node cryptographically signs the second data digest and returns a corresponding copy of a second signed second data digest;

receiving the second signed second data digests from the plurality of verification nodes;

retrieving the first signed first data digests from the public blockchain;

determining that the first signed first data digests match the second signed second data digests; and

in response to determining that the first signed digests match the second signed digests, sending a response to the request to retrieve stored data item, the response indicating that the stored data item has not changed since it was stored.

16. The system of claim 15 , wherein the plurality of verification nodes are computing devices participating in the public blockchain network.

17. The system of claim 15 , wherein the operations further comprise:

store a smart contract in the public blockchain, wherein the smart contract is configured to provide a monetary reward to the verification nodes in response to receiving the requested signed second data digests from the verification nodes.

18. The system of claim 15 , wherein generating the first data digest includes calculating a hash of the stored data item.

19. The system of claim 15 , wherein each verification node is configured to cryptographically sign the first data digest using a private key associated with that verification node.

20. The system of claim 15 , wherein sending the first data digest to the plurality of verification nodes includes broadcasting the first data digest to the public blockchain network.