High security lock core structure

A lock core comprising:

• a casing having a space defined axially therein and multiple top bead holes defined radially in the casing, the casing has at least one side bead hole which communicates with the space, the at least one side bead hole having a side bead unit located therein which has a side bead and a resilient member, the side bead having a neck and a flange, the resilient member mounted to outside of the side bead, and
• a core located in the space of the casing and having bottom bead holes defined radially therethrough and a keyhole defined axially therein, the keyhole communicating with the bottom bead holes which communicate with the top bead holes, each of the bottom bead holes having a stepped portion formed therein which is located corresponding to the flange of the side bead, a depth of each of the stepped portions being not larger than a total length of the neck and the flange.