https://www.vice.com/en_us/article/pkdjab/encrochat-signal-protocol-encryption

Encrypted phone firm Encrochat, whose customer base was primarily serious organized criminals, used the Signal protocol as part of its encrypted messaging application, according to a law enforcement document obtained by Motherboard.

The news highlights what law enforcement agencies may increasingly do when confronted with robust, end-to-end encryption like that of Signal: unable to read the content of intercepted messages, authorities may turn to hacking the end-point device, or phone, itself to siphon communications. In the Encrochat case, French police deployed malware to Encrochat phones and obtained the content of users' messages.