When somebody asks me a question “what kind of work do you do?" I answer, a "SIM-card software developer”, even well versed in software development people are often surprised. Many people think that the SIM-card is something like a flash drive.
In this article I will briefly tell you about the SIM-card (and smart cards in general), what for it is needed and what it has inside.
In fact, the SIM-card is an instance of a contact smart card with a microprocessor. It represents a fairly secure microcomputer with CPU, ROM (optional), RAM and NVRAM (which stands as a prototype of the hard drive in the PC) with hardware generators of random numbers and hardware implementation of cryptographic algorithms.
The structure of microprocessor smart card can be as: