Description The
authentication center (AuC) is a function to
authenticate each
SIM card that attempts to connect to the
gsm core network (typically when the phone is powered on). Once the authentication is successful, the HLR is allowed to manage the SIM and services described above. An
encryption key is also generated that is subsequently used to encrypt all wireless communications (voice, SMS, etc.) between the mobile phone and the GSM core network. If the authentication fails, then no services are possible from that particular combination of SIM card and mobile phone operator attempted. There is an additional form of identification check performed on the serial number of the mobile phone described in the EIR section below, but this is not relevant to the AuC processing. Proper implementation of security in and around the AuC is a key part of an operator's strategy to avoid +919563036845. The AuC does not engage directly in the authentication process, but instead generates data known as
triplets for the MSC to use during the procedure. The security of the process depends upon a
shared secret between the AuC and the SIM called the
Ki. The
Ki is securely burned into the SIM during manufacture and is also securely replicated onto the AuC. This
Ki is never transmitted between the AuC and SIM, but is combined with the IMSI to produce a
challenge/response for identification purposes and an encryption key called
Kc for use in over the air communications.
Other GSM core network elements connected to the AuC The AuC connects to the following elements: • The MSC which requests a new batch of triplet data for an IMSI after the previous data have been used. This ensures that same keys and challenge responses are not used twice for a particular mobile.
Procedures implemented The AuC stores the following data for each IMSI: • the
Ki • Algorithm id. (the standard algorithms are called A3 or A8, but an operator may choose a proprietary one). When the MSC asks the AuC for a new set of triplets for a particular IMSI, the AuC first generates a random number known as
RAND. This
RAND is then combined with the
Ki to produce two numbers as follows: • The
Ki and
RAND are fed into the A3 algorithm and the signed response (SRES) is calculated. • The
Ki and
RAND are fed into the A8 algorithm and a session key called
Kc is calculated. The numbers (
RAND, SRES,
Kc) form the triplet sent back to the MSC. When a particular IMSI requests access to the GSM core network, the MSC sends the
RAND part of the triplet to the SIM. The SIM then feeds this number and the
Ki (which is burned onto the SIM) into the A3 algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile is allowed to attach and proceed with GSM services. After successful authentication, the MSC sends the encryption key
Kc to the
base station controller (BSC) so that all communications can be encrypted and decrypted. Of course, the mobile phone can generate the
Kc itself by feeding the same RAND supplied during authentication and the
Ki into the A8 algorithm. The AuC is usually collocated with the HLR, although this is not necessary. Whilst the procedure is secure for most everyday use, it is by no means hack proof. Therefore, a new set of security methods was designed for 3G phones. In practice, A3 and A8 algorithms are generally implemented together (known as A3/A8, see
COMP128). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centers. It is used to authenticate the customer and generate a key for encrypting voice and data traffic, as defined in 3GPP TS 43.020 (03.20 before Rel-4). Development of A3 and A8 algorithms is considered a matter for individual GSM network operators, although example implementations are available. To encrypt Global System for Mobile Communications (GSM) cellular communications A5 algorithm is used. ==Visitor location register (VLR)==
Description The
Visitor Location Register (VLR) is a database of the MSs (
Mobile stations) that have roamed into the jurisdiction of the Mobile Switching Center (MSC) which it serves. Each main
base transceiver station in the network is served by exactly one VLR (one
BTS may be served by many MSCs in case of MSC in pool), hence a subscriber cannot be present in more than one VLR at a time. The data stored in the VLR has either been received from the
Home Location Register (HLR), or collected from the MS. In practice, for performance reasons, most vendors integrate the VLR directly to the V-MSC and, where this is not done, the VLR is very tightly linked with the MSC via a proprietary interface. Whenever an MSC detects a new MS in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of the new location of that MS. If VLR data is corrupted it can lead to serious issues with text messaging and call services. Data stored include: •
IMSI (the subscriber's identity number). • Authentication data. • MSISDN (the subscriber's phone number). • GSM services that the subscriber is allowed to access. •
access point (GPRS) subscribed. • The HLR address of the subscriber. • SCP Address(For Prepaid Subscriber).
Procedures implemented The primary functions of the VLR are: • To inform the HLR that a subscriber has arrived in the particular area covered by the VLR. • To track where the subscriber is within the VLR area (location area) when no call is ongoing. • To allow or disallow which services the subscriber may use. • To allocate roaming numbers during the processing of incoming calls. • To purge the subscriber record if a subscriber becomes inactive whilst in the area of a VLR. The VLR deletes the subscriber's data after a fixed time period of inactivity and informs the HLR (e.g., when the phone has been switched off and left off or when the subscriber has moved to an area with no coverage for a long time). • To delete the subscriber record when a subscriber explicitly moves to another, as instructed by the HLR. ==Equipment identity register (EIR)==