New details emerge of court case against Ladar Levison, founder of secure email service used by ex-NSA contractor Edward Snowden, as he hits halfway target to funding defence

Ladar Levison, the founder of secure email service Lavabit, has raised more than $20,000 to pay the legal fees incurred by a court battle to prevent government interference in his service.

The money already raised is half of the $40,000 target set by Levison, who says that "defending the constitution is expensive". Prominent donors so far include Apple blogger John Gruber, writer Merlin Mann, and Pinboard developer Maciej Ceglowski.

Edward Snowden, whose disclosures about NSA activities revealed extensive US electronic surveillance capability worldwide, was using a Lavabit email address when he announced a press conference at Moscow's airport. Recently uncovered documents also reveal that the site attracted the attention of the US Justice department just one day after Snowden revealed himself as the source of the Guardian's stories.

As a secure email service, Lavabit encrypted users' messages. The site acted as a trusted third party, with Levison enabling encryption services but not storing the private keys himself. For the government to eavesdrop on Lavabit's customers, it would have to force Levison either to store their private keys, or share the SSL certificate the site uses to keep communication between itself and users private.

However Levison abruptly closed Lavabit in August, writing in explanation to his customers that he refused "to be complicit in… crimes against the American people and the US Constitution," about which he was not permitted to speak further. At the time, he was not even able to confirm that there was a court case against him.

More details of that case, which will be heard in Virginia's 4th Circuit Court of Appeals, have become available – though "the entire record in the district court, including all applications, subpoenas, motions, warrants, and orders, remains under seal," the prosecutors say in a public filing.

That document shows the chronology of the government's dealings with Lavabit. Two specific orders stand out: a "pen register order", on 28 June, and an "order to show cause" on 9 July.

The former is an order to record data prospectively, storing requested details (for example, the metadata of emails) as they come in. The latter is typically used by the government to ask a court to enforce a demand which hasn't been complied with.

The judge whose orders Levison is challenging is Claude M. Hilton, the Senior US District Court Judge for the Eastern District of Virginia. Hilton served on the secret Foreign Intelligence Surveillance Court for seven years, until 2007.

Levison's opening brief in the appeal is due 3 October.

• This article was amended on 4 October 2013. The original gave the surname of the Lavabit founder as Levinson.