Sender Tasks

The sender first needs to define the following parameters for TESLA:

• The number of authentication chains
• The interval rate for each authentication chain
• The disclosure delay for each authentication chain

The number of authentication chains is dependent on the heterogeneity of network delay across receivers, the delay variance, and the desired authentication delay. For example, if we use TESLAin a LAN setting with a small network delay and low delay variance, the sender can use one single authentication chain with a disclosure lag of about one RTT, which can be as low as a few milliseconds. The other extreme is a radio broadcast over the Internet with millions of receivers. Some receivers will have high-speed network access with a low delay, others use dialup modem lines, and yet others might be connected through a wireless link with considerable delay, which can be on the order of seconds. To accommodate the latter category, which might also have a large synchronization error on the order of seconds, the longest authentication chain needs to have an disclosure delay as long as $15$ to $30$ seconds. Such a long delay is not acceptable to the high-speed users. A second authentication chain with a small disclosure delay around $1$ - $2$ seconds is appropriate. To close the wide gap between the high-end and the low-end users, a third chain with a delay of $5$ to $10$ seconds will appeal to the modem users.

Initially, the sender picks a random key $K$_n and computes and stores the entire chain of keys $K$_i = F(K_i+1).