On Thursday afternoon, an unnamed party filed a brief in the Fourth Circuit Court of Appeals. The appellant’s brief aims to resurrect Lavabit, the secure e-mail service famously used by the National Security Agency whistleblower Edward Snowden; the service promised its customers e-mail so secure that only the intended recipients could read it, and, in recent months, it has resisted government requests for information. After the government demanded encryption keys that would give it unfettered access to every Lavabit account, the company’s founder, Ladar Levison—the appellant, whose identity is technically under seal—shut the company down two months ago and vowed to “continue to fight for the Constitution.”

This summer, when the District Court for the Eastern District of Virginia ordered Levison to turn over the S.S.L. keys that would make the company’s communications and data readable by a third party, it did so in multiple ways—through what Levison’s lawyers call a “blizzard of dubious court orders.” The keys would have allowed the government secretly to read the e-mails of all of Lavabit’s customers, even though its investigation aimed to access the metadata from a single account. The government ordered Levison to install a pen-trap device, which records the routing information—e-mail addresses, IP addresses, and telephone numbers—going to and coming from a targeted Lavabit account, widely believed to be Snowden’s. It then argued that the device was useless without the keys. In response, the court issued a search-and-seizure warrant for the keys under the Stored Communications Act. Finally, a grand jury issued a subpoena, also demanding the keys. To win his appeal, Levison must rebut each of these demands.

Levison’s brief asks the Fourth Circuit to think of Lavabit as a digital city. The court sits in Richmond, Virginia, home to more than two hundred thousand people, while Lavabit, at its height, hosted the electronic data of more than four hundred thousand customers paying for total privacy. Levison’s lawyers argue that the order for Lavabit to turn over its master keys “is a truly dramatic act,” akin to “commanding the City of Richmond to give the police a key to every house within the city limits” in search of one man. Levison’s lawyers also compare Lavabit to a hotel forced to install “clear glass doors” for each room—even though the government knows that the crime occurred in Room 213. At the center of these analogies is Levison: the mayor, the hotel manager, the man whose promise of secure e-mail the government has ordered him to break.

Levison’s brief makes three core arguments. First, Levison argues that the pen-register order and Stored Communications statute do not require him to turn over the keys. Instead, Levison argues, they compel him only to install a pen register and a trap-and-trace device—the components of a pen trap—and turn over information about the targeted account. Language in the pen-register statute potentially requiring Levison to provide “technical assistance” does not mean that he needs to make the government’s surveillance efforts easy, his lawyer wrote: “What the government has argued is, in essence, that an innocent third party must provide whatever information might hypothetically be needed to make the government’s use of a pen-trap device effective—but that is not what the statute says.” E-mail companies are not required to be easy to wiretap, unlike telephone companies, which are, pursuant to the Communications Assistance for Law Enforcement Act.

Second, Levison argues that the Fourth Amendment forbids the government’s seizure of the private keys and access to all customers’ data. This is the case for two reasons, the brief argues: the keys are not themselves “the fruits, instrumentalities, or evidence of a crime,” which the government has traditionally been able to seize with probable cause. Instead, they are business secrets, “like Coca-Cola’s secret formula,” that enable Lavabit’s secure communications. “General rummaging through all of an innocent business’ communications with all of its customers is at the very core of what the Fourth Amendment prohibits,” Levison and his lawyers claim. Because the keys could expose the e-mail of all Lavabit users, Levison argues that the order is essentially “a modern-day writ of assistance”—a general warrant permitting the government to ransack all the digital homes in Lavabit City.

Finally, Levison claims that the subpoena requiring Lavabit to turn over its keys was unreasonable and oppressive: to comply with the government’s orders “would have either required Lavabit to perpetrate a fraud on its customer base or shut down entirely.” This, Levison claims, was a step too far: “Lavabit cannot exist as an honest company if the government is entitled to take this sort of information in secret.” That logic—that forcing Lavabit to assist government surveillance would create an “existential crisis” for the company—is as close as Levison gets to challenging orders that continue to limit his ability to talk about his circumstances.

To win, Levison must run the table. Even if he persuades the court that the subpoena is oppressive, he must still get the warrant invalidated, and then get the court to sign off on the installation of a pen-register without the keys. Among legal scholars evaluating his chances, early opinion suggests that it will be a “very uphill battle,” as the noted criminal-procedure scholar Orin Kerr put it.

When the court cloisters itself away with Levison’s brief, the government’s response brief—due on November 4th—and other legal texts, it should pause to consider the fact that, in many ways, we already live in Lavabit City, as the barrier between the “real world” and the “digital world” continues to dissolve. An e-mail, secured away in an encrypted inbox, conveys as much about us as a handwritten letter sealed away in a trusted drawer. The question is whether we have a right to lock the door.

Michael Phillips is an associate at a Wall Street litigation firm.

Illustration by Sipa/AP.