Apple has re-hired Jon Callas, a cryptography expert responsible for much of Apple's security technology over the years, the company confirmed on Tuesday.
Callas was brought back on in May, a spokesman told Reuters. Both he and Apple declined, however, to say what position he might take on in his latest employment.
Callas first worked with Apple in the 1990s, later returning between 2009 and 2011. Perhaps his core contribution to the company was full-disk encryption for OS X, although his full credits include work on both Mac and iOS security technologies.
Outside of Apple Callas is famous for his ties with PGP and Entrust, and co-founding encrypted communications firm Silent Circle. While mainly offering enterprise software, Silent Circle is best known to the public for its ultra-secure Blackphone devices.
Apple is presumably looking to strengthen the encryption used in OS X, iOS, and/or iCloud. Although those products are already thoroughly encrypted, the company has become increasingly concerned about hacking attempts by criminals, spy agencies, and other parties, whether foreign or domestic.
Various groups in U.S. law enforcement, intelligence, and politics have pursued Apple and other tech companies over encryption, claiming that communications are "going dark" because agencies can't intercept conversations mid-stream or decrypt them in local storage. One piece of proposed legislation would require backdoors, although another might restrict remote hacking by the FBI.
Apple periodically helps U.S. agencies retrieve data, but has actively fought any laws and court orders that might force it to weaken its encryption. Callas is known to support this view, but has proposed a compromise in which agencies can exploit zero-day vulnerabilities so long as they're later disclosed for fixing.