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Mottige Rat
Mottige Rat

Geregistreerd op: 14 Mei 2019
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BerichtGeplaatst: Di 23-06-2020 04:25:03    Onderwerp: Reageren met citaat


Every day millions of people use cellular phones over radio links. With the increasing features Nyheim Hines Hat , the mobile phone is gradually becoming a handheld computer. In the early 1980's, when most of the mobile telephone system was analog, the inefficiency in managing the growing demands in a cost-effective manner led to the opening of the door for digital technology (Huynh & Nguyen, 2003). According to Margrave (n.d), ?With the older analog-based cellular telephone systems such as the Advanced Mobile Phone System (AMPS) and the Total Access Communication System (TACS)? Tyquan Lewis Hat , cellular fraud is extensive. It's very simple for a radio hobbyist to tune in and hear cellular telephone conversations since without encryption, the voice and user data of the subscriber is sent to the network (Peng, 2000). Margrave (n.d) states that apart from this, cellular fraud can be committed by using complex equipment to receive the Electronic Serial Number so as to clone another mobile phone and place calls with that. To counteract the aforementioned cellular fraud and to make mobile phone traffic secure to a certain extent, GSM (Global System for Mobile communication or Group Special Mobile) is one of the many solutions now out there. According to GSM-tutorials Kemoko Turay Hat , formed in 1982, GSM is a worldwide accepted standard for digital cellular communication. GSM operates in the 900MHz, 1800MHz, or 1900Mhz frequency bands by 'digitizing and compressing data and then sending it down a channel with two other streams of user data, each in its own time slot.? GSM provides a secure and confidential method of communication.

Security provided by GSM

The limitation of security in cellular communication is a result of the fact that all cellular communication is sent over the air Quincy Wilson Hat , which then gives rise to threats from eavesdroppers with suitable receivers. Keeping this in account, security controls were integrated into GSM to make the system as secure as public switched telephone networks. The security functions are:

1. Anonymity: It implies that it is not simple and easy to track the user of the system. According to Srinivas (2001), when a new GSM subscriber switches on hisher phone for the first time, its International Mobile Subscriber Identity (IMSI), i.e. real identity is used and a Temporary Mobile Subscriber Identity (TMSI) is issued to the subscriber Malik Hooker Hat , which from that time forward is always used. Use of this TMSI, prevents the recognition of a GSM user by the potential eavesdropper.

2. Authentication: It checks the identity of the holder of the smart card and then decides whether the mobile station is allowed on a particular network. The authentication by the network is done by a response and challenge method. A random 128-bit number (RAND) is generated by the network and sent to the mobile. The mobile uses this RAND as an input and through A3 algorithm using a secret key Ki (128 bits) assigned to that mobile, encrypts the RAND and sends the signed response (SRES-32 bits) back. Network performs the same SRES process and compares its value with the response it has received from the mobile so as to check whether the mobile really has the secret key (Margrave, n.d). Authentication becomes successful when the two values of SRES matches which enables the subscriber to join the network. Since every time a new random number is generated, eavesdroppers don't get any relevant information by listening to the channel. (Srinivas Braden Smith Hat , 2001)

3. User Data and Signalling Protection: Srinivas (2001) states that to protect both user data and signalling, GSM uses a cipher key. After the authentication of the user, the A8 ciphering key generating algorithm (stored in the SIM card) is used. Taking the RAND and Ki as inputs, it results in the ciphering key Kc which is sent through. To encipher or decipher the data, this Kc (54 bits) is used with the A5 ciphering algorithm. This algorithm is contained within the hardware of the mobile phone so as to encrypt and decrypt the data while roaming. Algorithms used to make mobile traffic secure

Authentication Algorithm A3: One way function Darius Leonard Hat , A3 is an operator-dependent stream cipher. To compute the output SRES by using A3 is easy but it is very difficult to discover the input (RAND and Ki) from the output. To cover the issue of international roaming, it was mandatory that each operator may choose to use A3 independently. The basis of GSM's security is to keep Ki secret (Srinivas, 2001)

Ciphering Algorithm A5: In recent times, many series of A5 exists but the most common ones are A50(unencrypted), A51 and A52. Because of the export regulations of encryption technologies there is the existence of a series of A5 algorithms (Brookson Quenton Nelson Hat , 1994).

A8 (Ciphering Key Generating Algorithm): Like A3, it is also operator-dependent. Most providers combine A3 and A8 algorithms into a single hash function known as COMP128. The COMP128 creates KC and SRES, in a single instance (Huynh & Nguyen, 2003).

GSM security flaws

Security by obscurity. According to (Li, Chen & Ma) some people asserts that since the GSM algorithms are not publicized so it is not a secure system. ?Most security analysts believe any system that is not subject to the scrutiny of the world's best minds can't be as secure.? For instance T.Y. Hilton Hat , A5 was never made public, only its description is divulged as part of the GSM specification.

Another limitation of GSM is that although all communication between the Mobile station and the Base transceiver station are encrypted, in the fixed network all the communication and signalling is not protected as it is transmitted in plain text most of the time (Li, Chen & Ma).

One more problem is that it is hard to upgrade the cryptographic mechanisms timely.

Flaws are present within the GSM algorithms. According to Quirke (2004) ? A52 is a deliberately weakened version of A51, since A52 can be cracked on the order of about 216?.

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