Cold boxes were used to store valuables, such as security keys. The contents on a cold box could only be read by physically accessing the box and connecting it to a computer, making it a safe way to keep sensitive data off a network where slicers could access it.
The Bureau of Ships and Services within the Galactic Empire utilized cold boxes to store transponder data that was contraband to the public. One of these cold boxes ended up stolen and eventually found its way into Nebit's clan in 0 BBY/0 ABY.