Abstract: The disclosed embodiments provide a system that verifies user access to accounts. One example method involves: receiving a request to access a feature of a first account; obtaining, from a data repository, one or more transactions of a first account; obtaining, from the data repository, one or more transactions of a second account; matching at least one of the one or more transactions of the first account to at least one of the one or more transactions from the second account; generating a first verification of ownership of the first account by a user based on the matching at least one of the one or more transactions of the first account to the at least one of the one or more transactions from the second account; and enabling the user to access the feature of the first account based on the first verification of ownership.

Abstract: Certain aspects of the present disclosure provide techniques for summarizing data in a distributed system. Embodiments include generating an ordered list of blocks by iterating through a first group of blocks of a hash chain starting at a last block of the hash chain and adding each of the first group of blocks of the hash chain to the ordered list. Embodiments further include generating summary data by applying a summary function to the first group of blocks based on the ordered list. The summary function may take the ordered list as an input and provide the summary data of the first group of blocks as an output. Embodiments further include generating a summary block comprising the summary data and adding the summary block to a summary chain.