Prominent security expert and cryptographer Jon Callas returned to Apple, in the wake of the US company’s recent standoff with the FBI over opening a backdoor into the iPhone.

The rehiring of Callas, which was reported by Reuters, is a sign of Apple bolstering its security and privacy defences after recent events, and likely further confrontations with the US government in the future.

Callas rejoined Apple earlier this month, the company confirmed. He previously worked there between 1995 and 1997 on the firm’s encryption and data protection systems, and then again between 2009 and 2011.

In between times, he co-founded some well-known security firms, including PGP, Blackphone and Silent Circle. On 2 April, he tweeted “Last week was my last day-2-day w/Silent Circle. Yes, amicable. As an investor, I love the enterprise direction. Just going a different way.”

The previous month, he tweeted a single “Wow” about the US government’s decision to vacate a hearing in the case against Apple. The FBI worked with outside hackers to get into the iPhone belonging to one of the San Bernardino shooters.

It is unlikely to be the last such case. According to The Register, Callas will not be the only security expert taken on by Apple, with several more experts being approached.

And Apple will need their expertise, particularly as a Senate committee chews over legislation to require companies to help law enforcement agencies bypass encryption. And the presidential candidates are beginning to make their positions clear. Donald Trump called for a boycott of Apple over the issue. Hilary Clinton’s position is somewhat more nuanced.