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Hash Storage with KSI

Interledger component supports storing hashes to the Guardtime KSI blockchain using the Catena DB service. This can be used to e.g. improve privacy and provide auditability and transparency: private data is kept on a private ledger, while a hash of the data is stored on KSI to provide immutability for the data (if the original data is modified in any way, the hash verification would fail).

When using KSI with Interledger, the KSI Responder adapter of the Interledger component automatically calculates the hash over the data emitted in InterledgerEventSending() event, and stores this hash value to KSI, which in turn generates a new KSI signature. The resulting signature id will be passed to the sending ledger using the modified interledgerCommit() function described below. The signature can then be verified by the user using the Catena DB service.

Normally, the Responder adapter does no processing on the data payload, so this is also an example of how it is possible to create adapters that do some prosessing when it is relevant for that ledger.

Smart Contract Interface

In order to support reception of the KSI signature id, the Initiator ledger must implement a interledgerCommit() function with an additional data parameter that will be used to pass the KSI signature id, as shown in the InterledgerSenderInterface definition:

/**
 * @dev Function that will be called when the recipient has accepted the data,
 *      this function contains also an additional data parameter, which can be
 *      used to pass information to the Sender. Used by e.g. KSI Responder 
 *      to pass KSI id back to the Sender.
 * @param id The identifier of data sending event
 * @param data Arbitrary data as bytes
 */
function interledgerCommit(uint256 id, bytes memory data) public;

Configuration

The KSI can only be used as the destination ledger, so the Interledger setup must be unidirectional and direction parameter must be set to either left-to-right in which case KSI must be the right ledger, or to right-to-left in which case KSI must be the left ledger.

For ledger type = ksi, the required options in the configuration file are:

  • url: the URL for Catena signatures API;
  • hash_algorithm: the hash algorithm supported by Catena;
  • username: the username for Catena service;
  • password: the password for Catena service.

An example of the configuration file using left-to-right bridge between Ethereum and KSI:

[service]
direction=left-to-right
left=ethereum
right=ksi

[ethereum]
type=ethereum
url=http://localhost
port=7545
minter=0x63f7e0a227bCCD4701aB459b837446Ce61aaEb6D
contract=0x50dc31410Cae2527b034233338B85872BE67EEe6
contract_abi=./solidity/contracts/DataSender.abi.sol

[ksi]
type=ksi
url=https://tryout-catena-db.guardtime.net/api/v1/signatures
hash_algorithm=SHA-256
username=catena_username
password=catena_password