IBM has high hopes for blockchain technology. The IT giant announced on Tuesday a laundry list of plans to use blockchain tech and to help developers do the same. IBM (IBM) will offer tools through its cloud service for building blockchain apps, and it will open up IBM "Garages" in London, New York, Singapore and Tokyo for experts to collaborate with developers on blockchain tech.

Taken in tandem with the recent flurry of banks and financial institutions expressing public interest in blockchain, the technology is having a moment. In September, a slew of banks including BBVA, Citi, Credit Suisse, JPMorgan, Royal Bank of Scotland, and UBS all joined a coalition, led by a firm called R3, to implement blockchain technology in banking. In December, five more big names hopped on board, including BNP Paribas, ING, and Wells Fargo.

But the great irony of the banks' interest in blockchain is that the idea of a blockchain for traditional banking defeats the purpose of the blockchain—at least as it has been used thus far, with the digital currency bitcoin. And top executives from some of the very same institutions that have signed on to R3 have separately disparaged bitcoin.

To understand what it is that banks claim to want to do with blockchain, you first need to understand the bitcoin blockchain, which is a public, decentralized ledger that records every single bitcoin transaction. Think of it like a library card in the cloud (not the card you use to take out a book, but the slip inside a book that lists all the borrowers). If you send a friend $5 worth of bitcoin, the transaction goes on the blockchain. If one bitcoin startup acquires another bitcoin startup for $500,000 in bitcoin, that, too, goes on the blockchain. And you can view the blockchain in real time, as transactions are uploaded, at blockchain.info. Transactions are added in bundles, called "blocks," by "miners," who receive a tiny fee in bitcoin as an incentive to mine. Miners use large, expensive computers to find and mine the blocks.

The excitement of the bitcoin blockchain, to people in the digital currency world, is the potential for decentralized applications to be built on top of it that cut out the middle man. And the blockchain can be used to store and send anything of value, so there are companies using it to store documents like property deeds and even marriage licenses.

And now: Enter the banks. They've long stayed away from bitcoin, which has a toxic public image thanks to headlines about bitcoin being used in embezzlement and Ponzi schemes. (Think of Mt. Gox and Silk Road.) MasterCard CEO Ajay Banga said he believes bitcoin "starts bumping up against societal rules, which I worry about," and that, "it doesn’t give me the safety and security of knowing that I am who I am, and I’m paying who I know, which is what traditional currency does." And yet, MasterCard (MA) invested in Digital Currency Group, a venture firm that has itself invested in 65 different bitcoin and blockchain-enabled businesses. JPMorgan CEO Jamie Dimon said bitcoin "is going nowhere... There is nothing behind a bitcoin, and I think if it was big, the governments would stop it." And yet, JPMorgan (JPM) has signed on with R3.

Forget bitcoin, embrace blockchain

Bitcoin is doomed, if you ask Dimon. But the blockchain—now that's exciting. As Dimon said on CNBC last month, "The blockchain is a technology, which we’ve been studying... and yes, it’s real. If it proves to be cheap and secure it will be adopted for a whole bunch of stuff."

Translation: Blockchain is hot, bitcoin is not. We are seeing this sentiment again and again. IBM, in its extensive press release this week about its blockchain efforts, does not use the word "bitcoin" once. Bitreserve, a cloud banking vault launched by CNET founder Halsey Minor and led by former Barclays CIO Anthony Watson, was so eager to shed the stink of bitcoin that it changed its name to Uphold. Blockchain "is so hot right now," writes Erik Voorhees, the CEO of bitcoin startup Shapeshift, while bitcoin "has been left by the wayside, ignored like an embarrassing relative at a family gathering.” (And yet the price of bitcoin is up 24% in the last six months, 85% in the last six.)

What will using blockchain tech even look like for banks? R3's web site says its mission is "building and empowering the next generation of global financial services technology." That's pretty vague. David Rutter, CEO of R3 and a former executive at London-based electronic brokerage ICAP, has said R3 will help banks and financial firms use the "fabric" of blockchain technology.

You might think that people in the bitcoin world are pleased to see big, incumbent financial institutions embracing the underlying technology behind the leading cryptocurrency. They are not. Most of them see the banks' stated interest as empty lip service so far.

What most people believe the banks want to do is employ something like the blockchain in their record-keeping processes: record customer deposits and withdrawals on a blockchain as opposed to whatever (likely outdated) software they currently use. Sounds simple enough. But it would have to be a closed ledger, accessible only to customers of the banks. And therein lies the contradiction: the bitcoin blockchain is public and open-sourced; nothing about it is closed.

"I can see why banks are interested in using permissioned ledgers, and maybe it will make their back office more efficient," says Jerry Brito, executive director of digital currency nonprofit Coin Center. "But at the end of the day, it's not a very exciting innovation. The real innovation is a completely open and global ledger that is permission-less. Having a closed, permissioned ledger run by banks, that might allow for better auditing, but there’s no innovation there, you still have to go through a consortium to use the ledger." That is, what banks seem to want to do is incongruous to the purpose of the blockchain.

Digital Currency Group's Barry Silbert, who founded SecondMarket, which allowed for the trading of stocks in non-public companies, is similarly dubious of the "blockchain for banking" theme. "I’ve spoken quite publicly about my skepticism around the private blockchain approach," he tells Yahoo Finance.

If R3 doesn't yield innovative fruit, then why are banks rushing to join up? For starters, as a PR effort: once a few were involved, the others looked stodgy by delaying. But Brito also believes the interest will subside once banks actually learn more about blockchain technology. "I think right now investors are kind of waiting for Wall Street to get through this blockchain phase," he says. "They have blockchain fever and they need to just get over it. Because if they develop their own closed blockchains, soon they’ll all realize they want to talk to each other, and they’ll be back to square one, doing banking."

The bitcoin blockchain is open, global and permissionless. It has potential to serve as the backbone for additional exciting applications. If traditional banks want to employ it in their way, by acting as gatekeepers, it defeats the purpose. But don't expect that to dampen their public expressions of interest just yet.

This is the first in a three-part Yahoo Finance series about blockchain technology. The second part is about how you can invest in the blockchain; the third part is about the biggest names in the industry.

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Daniel Roberts is a writer at Yahoo Finance, covering sports business and technology.

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