The federal government and Apple both have dropped any semblance of civility in their battle over an encrypted iPhone, with the Department of Justice calling Apple’s arguments “corrosive” and threatening to demand the iOS source code and its master signing key for the operating system, and Apple’s lawyers calling the government “desperate”.

The government on Thursday filed a reply in federal court to support its motion compelling Apple to help it access an iPhone 5C used by Syed Farook, one of the alleged shooters in the San Bernardino killings last year. It’s the latest move in what has become a brutally contentious and public fight between Apple and the FBI over whether the company should be forced to build a compromised version of iOS that the FBI can install on the phone to bypass its security protections. Apple has refused to comply with a court order directing it to do just that, and the FBI and Justice Department have continued to push for the court to compel Apple to comply.

In the latest motion, the government said that it can’t get into the phone without Apple’s help, and that the company has engineered its software and hardware to make life as difficult as possible for law enforcement.

“Without Apple’s assistance, the government cannot carry out the search of Farook’s iPhone authorized by the search warrant. Apple has ensured that its assistance is necessary by requiring its electronic signature to run any program on the iPhone. Even if the Court ordered Apple to provide the government with Apple’s cryptographic keys and source code, Apple itself has implied that the government could not disable the requisite features because it ‘would have insufficient knowledge of Apple’s software and design protocols to be effective’,” the motion says.

“Apple’s rhetoric is not only false, but also corrosive.”

In its own court filings, Apple has said that what the government is asking the company to do is not only against Apple’s corporate policies, but also places an undue burden of time and money on the company. Building a new version of iOS to the FBI’s specifications would take several engineers as long as a month, the company said. The government dismissed those claims on Thursday and said that if Apple doesn’t comply with the court order, the government could demand the company’s source code and signing key instead.

“For the reasons discussed above, the FBI cannot itself modify the software on Farook’s iPhone without access to the source code and Apple’s private electronic signature. The government did not seek to compel Apple to turn those over because it believed such a request would be less palatable to Apple. If Apple would prefer that course, however, that may provide an alternative that requires less labor by Apple programmers,” the motion says.

“Apple’s rhetoric is not only false, but also corrosive of the very institutions that are best able to safeguard our liberty and our rights: the courts, the Fourth Amendment, longstanding precedent and venerable laws, and the democratically elected branches of government.”

Apple’s attorneys wasted little time in responding to the government’s assertions that the company is building security features into iOS to stop law enforcement from accessing phones.

“We add security features to protect our customers from hackers and criminals. And the FBI should be helping to support us in this because it keeps everyone safe. To suggest otherwise is demeaning. It cheapens the debate and it tries to mask the real and serious issues. I can only conclude that the DoJ is so desperate at this point that it has thrown all decorum to the winds,” Bruce Sewell, Apple general counsel, said in a call with reporters, according to The Verge.

This battle has brought legislators, technology executives, security experts, and many others into the ring, too. Rep. Ted Lieu (D-Calif.) has asked the FBI to withdraw its demands of Apple, and other tech companies, including Twitter and Facebook, have come out in support of Apple. Tim Cook, Apple CEO, said recently that he isn’t sure where this will end.

“I don’t know where this stops, but I do know this isn’t what should be happening in this country,” he said.

Image from Flickr stream of Håkan Dahlström.