Earlier this month Australia passed a law requiring companies to provide law enforcement access to their users' communications. Failure to comply under the Assistance and Access Bill could see firms fined AU$10 million and individuals AU$50,000.
But companies aren't required by the law to build a 'back door' into their apps which would make this possible.
Joshua Lund, a developer for messaging service Signal, said it's a "disappointing development".
"By design, Signal does not have a record of your contacts, social graph, conversation list, location, user avatar, user profile name, group memberships, group titles, or group avatars," he wrote in a blog.
"The end-to-end encrypted contents of every message and voice/video call are protected by keys that are entirely inaccessible to us. In most cases now we don't even have access to who is messaging whom."
In other words, they don't have any access to any of their users' messages, unlike the default setting on Facebook's Messenger service, or their identities. Nor can they build a secret back door for the authorities to access people's private chats because the Signal code is open source - that means it's public, and anyone can take a look at it.
- Five Eyes' call to end internet encryption spooks New Zealand privacy advocates
- NZ considers letting police access encrypted messages
Previous Australian Prime Minister Malcolm Turnbull is widely known to use Signal, and Mr Lund says new Prime Minister Scott Morrison will find it difficult to stop him using it.
"The Australian government could attempt to block the service or restrict access to the app itself. Historically, this strategy hasn't worked very well. Whenever services get blocked, users quickly adopt VPNs or other network obfuscation techniques to route around the restrictions.
"If a country decided to apply pressure on Apple or Google to remove certain apps from their stores, switching to a different region is extremely trivial on both Android and iOS. Popular apps are widely mirrored across the internet. Some of them can even be downloaded directly from their official website."
The head of the Australian Security Intelligence Organisation said in November the Assistance and Access Bill was "without question" needed, because encryption was getting in the way of 90 percent of its most important investigations.