Google has been expanding its range of SMS-style messaging services, presumably to keep step with other services such as WhatsApp, Telegram and, of course, the iOS equivalent. They include RCS and its associated end-to-end encryption feature that has been part of the Messages beta for a while now.
The Mountain View giant's updated support material advises users that messages with this level of encryption will show up in a dark shade of blue, whereas those without it will be in the normal light blue.
Messages with end-to-end encryption will also exhibit a new miniature lock icon along with their Send buttons and timestamps. Google asserts that this new facility ensures that content stays between a sender and recipient (and no-one else) thanks to on-device "secret keys".
They are generated for each individual encrypted message, and are deleted once a message reaches a recipient's phone. To use the new feature, both parties on the Messages app need to enable its chat features and ensure RCS is on via mobile data or Wi-Fi.