1 ▁tele phone - event / 8 0 0 0 ▁ ▁a = fmt p : 1 0 1 ▁ 0 - 1 1 ▁ ▁a = c rypto : 1 ▁A ES _ CM _ 1 2 8 _ H MA C _ SHA 1 _ 3 2 ▁inline : b mt 4 M z I z M m Y x dn F ya WM 3 d 2 8 2 d GR 5 Z 3 g 0 c 2 k 5 M 3 Y x ▁ ▁a = pt ime : 2 0 ▁ ▁a = send rec v ▁ ▁Disc uss ion : ▁Call ▁In iti ation ▁and ▁missing ▁End - to - End ▁Enc ryption ▁ ▁A ▁common ▁problem ▁with ▁secure ▁media ▁is ▁that ▁the ▁key ▁exchange ▁might ▁not ▁be ▁finished ▁when ▁the ▁first ▁media ▁packet ▁arriv es . ▁In ▁order ▁to ▁avoid ▁initial ▁clicks , ▁those ▁packets ▁must ▁be ▁dropped . ▁Usually ▁this ▁is ▁only ▁a ▁short ▁period ▁of ▁time ▁( below ▁ 1 0 0 ▁ms ), ▁so ▁that ▁this ▁is ▁no ▁major ▁problem . ▁ ▁The ▁S DE S ▁method ▁does ▁not ▁address ▁the ▁" end - to - end " ▁media ▁encryption . ▁For ▁example , ▁if ▁user ▁A ▁is ▁talking ▁to ▁user ▁B ▁via ▁a ▁proxy ▁P , ▁S DE S ▁allows ▁neg ot iation ▁of ▁keys ▁between ▁A ▁and ▁P ▁or ▁between ▁B ▁and ▁P , ▁but ▁not ▁between ▁A ▁and ▁B . ▁For ▁end - to - end ▁media ▁security ▁you ▁must ▁first