Global System for Mobile communication
GSM – the Global System for Mobile communication 1 – is a standard
developed by the
European Telecommunications Standards Institute
to describe a digital switched-circuit network that is optimised for full-duplex
voice telephony, also known as 2G (second generation).
The first 2G network was installed in December 1991 in Finland, and in the rest
of Europe during the course of the following year .
In the Netherlands, the introduction of
GSM was delayed until 1994.
Originally: Groupe Spécial Mobile (French).
Although initially developed as a pan-European system, GSM quickly grew
out to an international standard, which even got adopted in the US.
Over the years, the standard was expanded with new frequency ranges
(e.g. 1800 MHz) and with provisions for data transfer, GPRS, video and
internet. This led to the introduction of the 3G
UMTS standard –
developed by the 3GPP
– and the 4G
LTE Advanced standard, which are
no longer part of the original ETSI GSM standard.
In 2019, steps were taken to move to the next standard which will
be a broadband system known as 5G (fifth generation).
It was first rolled-out in South-Korea and is backward compatible
with 2G, 3G and 4G. China has heavily invested in the developed of
5G equipment, but many countries have restricted or eliminated the
use of Chinese 5G equipment because of espionage fears .
One of the key features of GSM is the Subscriber Identity Module (SIM)
– also known as a SIM card – which contains the user's
identity, known as the International Mobile Subscriber Identity (IMSI).
This is different from the phone's own identity, which is known as
International Mobile Equipment Identity (IMEI). This allows stolen
phones to be blocked without losing the telephone number.
GSM is a fully digital system that uses CODECs for converting analogue
speech into digital data. In addition, the digital data is encrypted with
a high-end encryption algorithm that can not be broken easily (1990)
but is prone to several attacks,
including man-in-the-middle attacks .
For lawful interception, a so-called IMSI-catcher can be used for
The initial GSM development was an initiative of several
European telecommunications providers, including the Norwegian Nordic Telecom
and the Dutch PTT
Later, French and British providers were involved as well.
Following the experiences with their earlier 1G networks – which
were based on the Nordic NMT standard –
the Dutch PTT and Nordic Telecom
advocated the use of strong encryption and authentication,
in order to prevent clandestine use and eavesdropping.
According to former KPN developer Peter van der Arend in an article
on the Dutch website Tweakers , it was initially
planned to use a 128-bit encryption for the first version of the GSM standard
– known as A5/1 – but this was reduced after an intervention by the
British intelligence service GCHQ.
initially, GCHQ wanted the encryption to be reduced to 48-bits, but
a compromise was later reached at 54-bits, presented as a 64-bit key
of which the last 10 bits are ignored.
The 54-bit encryption of the original GSM standard is no longer
considered safe, and it is known that (cheap) hardware was available
around 2010 to make eavesdropping of GSM conversations possible .
The encryption algorithm has since been replaced by stronger alternatives.
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© Crypto Museum. Created: Sunday 19 May 2019. Last changed: Saturday, 12 August 2023 - 14:08 CET.