swift - Pairing in Core Bluetooth Peripheral application iOS -

i have created application in iphone can act ble peripheral.i want initiate pairing mechanism when central send request connect. have searched on net , came know individual characteristic can encrypted , initiate pairing when read central. have read bluetooth 4.0 , 4.1 security document saying there various pairing mechanism available.but don't know how use in application. can help?

code using creating characteristic

var characteristic = cbmutablecharacteristic(type: charid, properties: charproperties, value: nil, permissions:cbattributepermissions.readencryptionrequired|cbattributepermissions.writeencryptionrequired)