应该是的。
"Signal is generally considered to be one of the most secure messaging apps available. It's open source, uses end-to-end encryption by default, and unlike WhatsApp, it doesn't store any message metadata or use the cloud to back up messages. "
正如打开手机的WhatsApp,WhatsApp就表明:" Messages and calls are end-to-end encrypted. No one outside of this chat, not even WhatsApp, can read and listen to them."