An enterprise security system is improved by instrumenting endpoints to explicitly label network flows with cryptographically secure labels that identify an application or other source of each network flow. Cryptographic techniques may be used, for example, to protect the encoded information in the label from interception by third parties or to support cryptographic authentication of a source of each label. A label may provide health, status, or other heartbeat information for the endpoint, and may be used to identify compromised endpoints, to make routing decisions for network traffic (e.g., allowing, blocking, rerouting, etc.), to more generally evaluate the health of an endpoint that is sourcing network traffic, or for any other useful purpose.