If I go missing, can the police access my private messages?

The father of missing Belgian backpacker Theo Hayez has begged WhatsApp to hand over his son’s messages to the police, hoping they will hold clues to his whereabouts. The messaging service said it wants to help but doesn’t have access to his communications.

NSW police know that 18-year-old Theo Hayez used the messaging service WhatsApp on the night he disappeared, with his mobile phone last used in the Cape Byron area on 1 June. Police haven't been able to read his messages.

The backpacker has not been seen since 31 May when he left local nightclub Cheeky Monkeys. He was reported missing by staff at the WakeUp! Backpacker hostel on 6 June.

In a heartbreaking statement Theo's father, Laurent, said the messages would help generate leads for NSW police, who are baffled by the disappearance of the teen.

"I promised Theo's little brother that I would bring his brother home. Please, help me keep my promise to him," Mr Hayez said through his tears.

WhatsApp is owned by Facebook and allows users to send text messages, voice messages, and make calls.

The tech giant says it's working with authorities, but accessing the information is not straight forward.

Belgian backpacker Theo Hayez, who vanished in Byron Bay in May.
The father of missing Belgian backpacker Theo Hayez has appealed for anyone to come forward with information.
AAP

Can WhatsApp hand over my messages?

The ability of tech companies and authorities to access your private messages is dependent on the law and whether the messages are encrypted.

WhatsApp can only access and disclose some information which can include a user's name, last seen date, IP address and basic information. But not the contents of messages.

Even if the company wanted to handover Theo's messages, it simply can't because it uses end-to-end encryption.

What is end-to-end encryption?

With most messaging services, information is passed and stored by third parties, then retrieved by the recipient. The information is not encrypted, so this allows the third party to access your messages. Gmail, Facebook messenger and Instagram messenger are not encrypted messaging services.

If you went missing, the "third party" could technically to hand over messages to authorities, if police gained a warrant to access the information.

But if you use an end-to-end encryption service, like WhatsApps, only the sender and the recipient(s) can read the contents. The sender "negotiates" a "key" with the receiver which unlocks the messages. This "key" is only accessible by the sender and receiver.

Laurent Hayez, father of missing Belgian backpacker Theo.
Laurent Hayez has pleaded to the public to help find his son Theo who went missing in Byron Bay.
AAP

Even WhatsApp cannot read your messages, because it doesn't have the "key".

Australia has laws which require providers to hand over communication to police when requested within the law. Controversial legislation passed in December compelled companies like Facebook to allow police to access encrypted messages.

Data and IT expert Vanessa Teague from the University of Melbourne said that despite the law, WhatsApp cannot handover messages they simply can't access.

"Anyone who understood the technology at the time knew that it was unrealistic tech companies like Facebook could access their encrypted messages," she said.

CCTV footage of missing Belgian backpacker Theo Hayez has been released by police
CCTV footage of missing Belgian backpacker Theo Hayez has been released by police
Supplied

"It doesn't matter what the law says, if the technology is secure, you cannot decrypt properly encrypted messages."

The new legislation can force tech companies to build tools to intercept encrypted information, if they are unable to access messages.

Professor Teague said it is unclear is police have exercised this new power, but it isn't relevant in the case of a missing person, as the messages have already been sent.