We describe a new class of lightweight. symmetric-key digital certificates called extended TESLA certificates and a source authentication protocol for wireless group communication that is based on the certificate. The certificate binds the identity of a wireless smart device to the anchor element of its key chain; keys from the chain are used for computing message authentication codes... https://www.hindigyanvishv.com/limited-time-SYIL-X7-Vertical-Mill-big-deal/