Wireless Access Security (1)

Since the development of wireless communication technology, various wireless standard wireless systems have brought many security risks. So how can we ensure the security of wireless access? Next, we will introduce in detail various wireless access security mechanisms, principles, and processes.

Wireless Access Security of the 3GPP system

Wireless Access Security for GSM/GPRS/EDGE Systems
In the GSM/GPRS/EDGE system, the user's SIM card shares a security key Ki128bit with the HLR/AuC of the destination network. Based on this key, the network can authenticate the user, however, the user cannot authenticate the network, and the wireless link can be encrypted between the base station and the mobile phone.

The authentication and encryption of the GSM/GPRS system are implemented based on the RAND, SRES, and Kc. The basic process is as follows.
1. When the user needs to be authenticated, the MSC/VLR of the service network requests the authentication vector from the HLR/AuC to the user.
2. HLR/AuC first generates a random number RAND, based on this RAND and the user's Root Key Ki, calculates the authentication response SRES that the Mobile Server should return based on the A3 algorithm, based on the RAND and user's Root Key Ki, the A8 algorithm is used to calculate the subsequent key Kc used for encryption. HLR/AuC may also generate multiple sets of such authentication vectors.
3. HLR/AuC returns one or more RAND, SRES, Kc) triplet to the MSC/VLR or SGSN of the service network.
4. the MSC/VLR or SGSN of the service network sends an authentication request to the user's mobile phone through the NAS non-access sub-layer) signaling. The parameter contains a RAND received in step 3.
5. the mobile phone transfers the authentication request to the SIM card through the RunGSMAlgorithm command. the SIM card uses the A3 algorithm to calculate the authentication response SRES Based on the RAND and the secure Root Key Ki ', calculate the encryption key Kc using the A8 Algorithm Based on both RAND and Ki.
6. the SIM card returns SRES and Kc to the mobile phone, and saves Kc to a readable file EF (Kc) on the card.
7. The terminal returns SRES to the service network. The MSC/VLR or SGSN of the service network compares it with the SRES received in step 3. If the SRES is the same, the user authentication succeeds. Otherwise, the authentication fails. The MSC/VLR or SGSN of the service network forwards the Kc to the base station.
8. When you need to encrypt the blank port communication, the access network of the terminal and the service location negotiates the encryption algorithm, which is usually called A5 algorithm negotiation. The standard requires that 2G terminals must support the A5/1 algorithm and the recommended A5/3 algorithm.
9. the access network obtains the encryption key Kc from the core network of the service location. The terminal reads the Kc from the card and uses it as the key to calculate the random number using the negotiated A5 algorithm, it is then used for the encryption and decryption of empty port messages/data.

Wireless Access Security of the UMTS system

2G Access Security has the following shortcomings.
1. only the network can authenticate users and cannot authenticate the network. Malicious networks may trick users into logging in/using the network, steal user information, and spread junk/virus information.
2. after the PIN code is verified, the SIM card will calculate the corresponding SRES authentication response for all RunGSMAlgorithm commands according to the random number entered in the command, attackers can exploit this vulnerability to initiate brute-force attacks, especially structural enumeration attacks, to reverse the User Key Ki.
3. There is no integrity protection, and there is a threat that messages/data are intercepted and tampered in the middle.
4. Some old algorithms can be replaced by new algorithms with higher security levels.

3G system for the above deficiencies are targeted improvements, in the UMTS including WCDMA and TD-SCMDMA) system, the user's USIM card and destination network HLR/AuC share a security key K128bit ), based on this key, the network can authenticate users, and users can also authenticate networks. In addition, the base station and mobile phone can encrypt and protect wireless links.
The two-way authentication, encryption, and integrity protection of the rabbitumts system is implemented based on the RAND, XRES, CK, IK, AUTN) quintuple. The basic process is as follows.

1. When the user needs to be authenticated, the MSC/VLR of the service network requests the authentication vector from the HLR/AuC to the user.
2. HLR/AuC first generates a random number RAND and a SQN. Then, based on the RAND, SQN, and the user's root key K, the following calculations are performed as shown in Figure 1: the f2 algorithm is used to generate the authentication response XRES that the Mobile Server should return, the f3 algorithm is used to generate the encryption key CK, and the f4 algorithm is used to generate the Integrity Protection key IK, the authentication response AUTN corresponding to the network is generated using the f1 and f5 algorithms. HLR/AuC may also generate multiple sets of such authentication vectors.
3. HLR/AuC returns one or more RAND, XRES, CK, IK, AUTN) quintuple to the MSC/VLR or SGSN of the service network.
4. the MSC/VLR or SGSN of the service network performs AKA authentication and key agreement through the NAS non-access sub-layer) signaling and the user's mobile phone/UISM card.
5. When it is necessary to encrypt or protect the integrity of the blank port communication, the terminal and the access network RNC in the service location negotiate and activate the security mode.
6. the access network obtains CK and IK from the core network of the service location. The terminal obtains CK and IK from step 4 or reads CK and IK from the card and uses them as keys respectively, then, the f8 and f9 algorithms are used for encryption/decryption and Integrity protection. Terminals and access networks can also use Integrity Protection IK and f9 algorithms to implement simple local authentication.