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A cryptocurrency expert who gave a talk at a Pyongyang conference has admitted conspiring to help North Korea evade sanctions.

Virgil Griffith, a former senior researcher with the Ethereum Foundation, pleaded guilty on Monday.

The US Department of Justice he had "jeopardised the national security of the United States" by undermining sanctions.

His lawyer told the Wall Street Journal Griffith was "sincerely remorseful."

In April 2019, Griffith attended the Pyongyang Blockchain and Cryptocurrency Conference, with about 100 other attendees.

He had applied for permission to travel to North Korea - but when this was refused, he went anyway, reaching the country via China.

Seven months later, Griffith, who had been living in Singapore, was arrested at Los Angeles International Airport.

Griffith, had given a presentation on blockchain technology and cryptocurrency, with topics approved by North Korean officials, and "participated in discussions regarding using cryptocurrency technologies to evade sanctions and launder money".

The title of the presentation was Blockchain and Peace.

Blockchain is the technology underpinning cryptrocurrencies, in effect a giant shared ledger of transactions.

After Griffith's arrest, Ethereum cryptocurrency co-founder Vitalik Buterin circulated a petition in support of him, which attracted only modest support.

In the Twitter thread, Mr Buterin said the foundation had not supported Griffith's activities in North Korea, saying: "It was Virgil's personal trip, that many counselled against".

On Monday, Griffith pleaded guilty to conspiring to violate the US International Emergency Economic Powers Act by providing services to North Korea, including technical advice on using cryptocurrency and blockchain technology to evade sanctions, according to a Department of Justice statement.

Griffith's presentation, the , had among other things, focused on "how blockchain technology such as 'smart contracts' could be used to benefit the DPRK [North Korea], including in nuclear weapons negotiations with the United States".

US Attorney Audrey Strauss said Griffith had agreed to help "one of our nation's most dangerous foreign adversaries, North Korea".

"Griffith worked with others to provide cryptocurrency services to North Korea and assist North Korea in evading sanctions, and travelled to North Korea to do so," Ms Strauss said.

Griffith, who will be sentenced in January, faces up 20 years in jail but his plea will probably mean his final sentence is considerably shorter.

Ethan Lou a journalist who attended the conference in North Korea and is following the trial, said the admission of guilt was a "plea deal with up to six and a half years in prison".

"Virgil was quite emotional - deep sighs sometimes when he spoke," he .

Griffith, who has a PhD from the California Institute of Technology, worked for the Ethereum Foundation's Special Projects group before his arrest.

On his now defunct personal website, he said his personal goals were "expose corruption, curb abuses of power, and with 'gloves off' ensure the digital age never becomes a digital dystopia".

He first rose to wide public attention as the creator of Wikiscanner, a tool that made it easy to discover, often embarrassing or self-serving, made on computers belonging to well known organisations including the CIA, the Vatican, the Ministry of Defence and the Â鶹¹ÙÍøÊ×Ò³Èë¿Ú.

Griffith also appeared in reality-TV programme King of the Nerds.

His lawyer, Brian Klein, said he had "many wonderful qualities, and no-one should define him by this mistake".