A computer-based method includes transmitting a packet from a source across a packet-switched network that includes multiple network switches, and attaching, or otherwise associating, a unique signature to the packet at one or more of the network switches. Each unique signature identifies a corresponding one of the network switches, through which the packet passes as it travels from the source toward a destination. The packet and an attached, or otherwise associated, string of signatures from the plurality of network switches, is received at or near the destination in the packet-switched network. In a typical implementation, the validity of the packet is checked, by a validator (e.g., at or near the destination).