I . The TESLA Broadcast Authentication Protocol

One of the main challenges of securing broadcast communication is source authentication, or enabling receivers of broadcast data to verify that the received data really originates from the claimed source and was not modified en route. This problem is complicated by mutually untrusted receivers and unreliable communication environments where the sender does not retransmit lost packets. The authors present TESLA (Timed Efficient Stream Loss-tolerant Authentication), an efficient broadcast authentication protocol with low communication and computation overhead. TESLA scales to large numbers of receivers and tolerates packet loss. It is based on loose time synchronization between the sender and the receivers, and uses only symmetric cryptographic functions. Still, and as is demonstrated herein, TESLA has possible