who invented the sim card
Answers
Answer:
(4^0 + 4^-1) × 2^2(4^0 + 4^-1) × 2^2
Explanation:
(4^0 + 4^-1) × 2^2
(4^0 + 4^-1) × 2^2
A SIM card, or Subscriber Identity Module is a familiar element of a mobile phone. It can be easily swapped or replaced, yet, it was not born at the same time as the cellular phone.
The first mobile phones used to support only embedded communication standards: the subscription parameters were hard-coded into the mobile terminal’s memory.
The oldest analogue standards like NMT-450 did not employ any means of security: the subscription data could be copied into another device and cloned, making it possible to call and accept calls on the rightful owner’s behalf, free of charge.
The first means of security, which was invented a bit later, was the so called Subscriber Identity Security (SIS) code an 18-digit number which was unique to a device and hard-coded into an application processor.
SIS codes used to be evenly distributed among the vendors so two devices could not share the same SIS code. The processor also stored a 7-digit RID code which was transmitted to a base station when a subscriber registered to a cellular network.
The base station would generate a random number, which, bundled with a unique SIS response, SIS processor would use to produce the authorization key. Both keys and numbers were relatively short but adequate for 1994 quite predictably.
The system was later cracked, just three years before the GSM (Global System for Mobile Communications) standard emerged. It was more secure by design as it used a similar, yet more cryptically resilient authorization system.
The standard thus became detached. This meant that the authorization was then fully performed on an external processor integrated into a smart card. The resulting solution was called
With the introduction of SIM cards, the subscription was no longer dependent on the device so a user could change devices as frequently as wished, while preserving the mobile identity.
