Apple's showdown with the Justice Department is different in one important way. Now that the government has tried to force Apple to hack its own code, security officials say, the company must view itself as the vulnerability. That means engineers will have to design a lock they absolutely cannot break.
"This is the first time that Apple has been included in their own threat model," Mr. Zdziarski said. "I don't think Apple ever considered becoming a compelled arm of the government."
The F.B.I. director, James B. Comey Jr., signaled this week that he expected Apple to change its security, saying that the phone-cracking tool the government sought in the San Bernardino case was "increasingly obsolete." He said that supported the government's argument that it was not seeking a skeleton key to hack all iPhones.
Apple, though, says the case could set a precedent for forcing company engineers to write code to help the government break any iPhone. "The U.S. government has asked us for something we simply do not have, and something we consider too dangerous to create," Mr. Cook said in his letter.
The heated back-and-forth between the government and technology companies is, at least in part, a function of the Obama administration's strategy. The White House has said it will not ask Congress to pass a law requiring tech companies to give the F.B.I. a way to access customer data. That has left the Justice Department to fight for access one phone at a time, in court cases that often go unnoticed.
While it is generally accepted that Silicon Valley's tech giants can outgun the government in a technical fight, the companies do face one important limitation. Security features often come at the expense of making products slower or clunkier.
Apple's brand is built around creating products that are sleek and intuitive. A security solution that defeats the F.B.I. is unworkable if it frustrates consumers. One of the impediments to encrypting all the data in Apple's iCloud servers, for instance, has been finding a way to ensure that customers can easily access and recover photos and other information stored there.
"Telling a member of the public that they're going to lose all the family photos they've ever taken because they forgot their password is a really tough sell," Mr. Soghoian said. "A company wants to sell products to the public."