Since the heady days of late 2017 and January of this year, cryptocurrencies have gone into retreat. Bitcoin, the best-known example, is now worth just a third of its value at its peak.
But there remain plenty of true believers in digital currencies. They point out that prices are still well above where they were in 2016. And interest from institutional investors is still strong enough for analysts to want to make sense of the crypto-phenomenon.
The latest bank to take a shot is Barclays, which devotes a lot more of its "Equity Gilt Study 2018" to the impact of technological change on finance and the economy than it does to either equities or gilts. Its report describes crypto-technology as "a solution still seeking a problem".
It identifies four challenges in particular. The first is trust. In most countries, consumers and businesses have faith in the currencies issued by the government.
The second is sovereignty: the potential for tax avoidance and loss of financial control means that neither governments nor central banks will be keen to see private cryptocurrencies take off.
A third challenge is privacy. Although they can be used pseudonymously, cryptocurrencies are less reliably anonymous than cash since the blockchain that lies behind them records all transactions. If a pseudonym is cracked, the user's purchase history is revealed. A fourth relates to the ability to undo a transaction in cases of error or fraud — blockchain transactions are hard to reverse.
On top of all these problems is the fact that existing alternatives seem to work perfectly well. It is easy to make payments and transfer money in an instant.
So what is the appeal of digital newcomers? Private cryptocurrencies can be attractive in societies where trust is low, or where governments are unwilling or unable to provide reliable means of exchange — in wartime or during periods of sovereign default, for example. Barclays also suggests that in countries where opportunities to invest are limited, "cryptocurrencies may be one of the few ways to diversify savings out of domestic assets."