SAN FRANCISCO (Reuters) - The U.S. government is trying to force Facebook Inc (FB.O) to break the encryption in its popular Messenger app so law enforcement may listen to a suspect’s voice conversations in a criminal probe, three people briefed on the case said, resurrecting the issue of whether companies can be compelled to alter their products to enable surveillance.<br><br>Ordinary Facebook text messages, Alphabet Inc’s (GOOGL.O) Gmail, and other services are decrypted by the service providers during transit for targeted advertising or other reasons, making them available for court-ordered interception.<br><br>End-to-end encrypted communications, by contrast, go directly from one user to another user without revealing anything intelligible to providers.