How do you bypass ignition security without the key?

It depends on the vehivcle. Many of the newer (post 1970) models contain redundant wiring and features like locking steering wheels so that even if you manage to start a car without the key, it won't shift into gear or allow you to steer it. Typically you can try hammering a flathead screwdriver into the key slot and forcing it to turn with some bicep action and a pair of vicegrips. Alternatively, you could unbolt the steering wheel, dissasymble the column, and replace all the parts with new ones you have a key for.