In the past there are many way to extract know-how from tampered device.
Today need an effort that only a million $ company can do.
In your example, smart card, today have a tamper evidece mechanism, and tamper proof shield.
In the past, you can decap the silicon using a special solvent and observe with microscope a memory map (the memory map in PROM or FLASH is visible by microscope. you can see if the gap is filled or not, or junction fused or not) also you can make a look for the hardware, and reverse it.
Today, the silicon is coverd after passivation, by a metal film, that can't be removed by solvent and if you try to remove it mechanically, you damage the silicon.
Also there are a tamper evidence mechanism that erase all memory if you try to decap it.
Also the secrets are stored in EEprom and this kind of memory contents is not visible by microscope.
Finally, the loose made by piracy, costrain the major to change protection and secret, frequently, then if you discover after many effort some secrets, the system will be changed befor your discovered it.
Today the mission to reverse smart-card is too hard for a home user or a hobbyst, but, as ever succeeded, there are many BUG in firmware or hardware and if you are luky you can discover one of this, and try to extract secret with this back door.
But unlikely, there are not standard backdoor, you need to find the particular backdoor of this hardware/firmware.
In many cases in the past, it is discoverd for fortuite issues, trying to do a legal action, and some users retrieved secrets.
For reverser the road is very difficult now.
Good Luck !!
bye