It has just concluded a three-month trial of the technology with Japanese IT company Fujitsu.
Mizuho used the Open Assets Protocol in its trial to encapsulate the type and number of financial instruments being traded, the amount due and the currency used, the country of settlement, and the transaction date. The encapsulated data was then added to a blockchain as a new transaction, providing a tamper-resistant record of the trade.
The best-known use of blockchain technology is the worldwide public ledger of bitcoin transactions, but a number of banks and trading exchanges are experimenting with their own private blockchains to record other kinds of information.
A blockchain is a record of transactions, each block in the record containing a computational "hash" of itself and of the previous block so that all are connected like links in a chain.
The hash is a digital digest of a block of data, determined using a hash function. Calculating the function for a given chunk of data is easy, while creating a block of data with a given hash is hard. Adding a new block to the chain involves solving the computationally difficult task of creating a block containing a hash that is also the hash of the block itself.
The blockchain record is distributed across a network of computers, which compete to gather up new transactions submitted to the network into blocks, validating them by calculating a hash that will complete the block. In the bitcoin system, this process is called mining.
While it's not impossible to modify the transaction record, going back in the blockchain to modify or fake a past transaction involves performing that validation process on all blocks from the modified one to the latest one, before another machine can add a new, legitimate transaction to the end of the chain.
Mizuho has used the Open Assets Protocol only in a trial so far, but other financial institutions are already using it in live systems.
Nasdaq uses it to store and vouch for the authenticity of documents in its own blockchain system, Linq, which last December recorded the issuance of shares by Chain.com to a private investor. Later this year, Nasdaq plans to use the protocol to speed the recording of stockholders' electronic votes for companies listed on its exchange in Tallinn, Estonia.
Speed was the motivation for Mizuho's trial. Because of the difficulties in verifying the authenticity of electronic orders in cross-border securities trades, transactions typically take three days to complete, exposing all parties to the risk of price or currency fluctuations.
With a blockchain-based ledger, Mizuho can complete transactions on the same day, it said Tuesday.
While other approaches can speed up such transactions, they typically involve a centralized system. In a blockchain system, each machine storing or adding to the blockchain behaves independently, with the validity of the record determined by consensus among all the machines.
This decentralized approach keeps cost down, according to Fujitsu and Mizuho.
In the trial, the system was run entirely in Fujitsu's cloud infrastructure, but in principle there is nothing to stop other banks or infrastructure providers from participating and submitting their own transactions by running their own instances of the system.