Sign in Subscribe

CK (Ciphering key)

Last updated on 

Introduction:

Ciphering key (CK) is a term commonly used in the field of telecommunications and wireless communication networks. It refers to a secret key that is used in the encryption and decryption of wireless communication data. The CK is one of the primary components of the Authentication and Key Agreement (AKA) mechanism, which is used in the Universal Mobile Telecommunications System (UMTS) and the Long-Term Evolution (LTE) wireless networks. In this article, we will discuss the CK in detail, its purpose, and its application in the wireless communication networks.

What is Ciphering Key (CK)?

A Ciphering key (CK) is a secret key that is used in the encryption and decryption of data exchanged between the user equipment (UE) and the base station (BS) in the wireless communication networks. The CK is one of the parameters used in the AKA mechanism, which is a security protocol used to authenticate and establish a secure communication link between the UE and the BS. The CK is derived from the authentication vector (AV) that is generated during the AKA procedure.

Purpose of Ciphering Key (CK):

The main purpose of the CK is to provide confidentiality and integrity to the data exchanged between the UE and the BS in the wireless communication networks. The CK is used to encrypt and decrypt the user data and control information transmitted between the UE and the BS. The CK is also used to generate the message authentication code (MAC), which is used to ensure the integrity of the data transmitted over the wireless channel.

How is Ciphering Key (CK) generated?

The Ciphering key (CK) is generated during the AKA procedure, which is initiated when the UE attempts to establish a connection with the BS in the wireless network. The AKA procedure involves the following steps:

  1. Authentication Request: The UE sends an authentication request to the BS, which includes the identity of the UE and a random challenge number (RAND).
  2. Authentication Response: The BS generates an authentication vector (AV) that contains the RAND, a signed response (SRES), and the CK. The AV is then sent to the UE.
  3. Verification: The UE verifies the authenticity of the AV by computing the SRES using the RAND and a secret key (K) that is stored in the subscriber identity module (SIM) card. If the computed SRES matches the SRES in the AV, the UE accepts the AV and derives the CK from it.
  4. Key Derivation: The CK is derived from the AV using a function that takes the RAND and the K as inputs. The function is specified in the 3rd Generation Partnership Project (3GPP) technical specification.

Application of Ciphering Key (CK):

The Ciphering key (CK) is used in the encryption and decryption of the user data and control information transmitted between the UE and the BS in the wireless communication networks. The CK is also used to generate the message authentication code (MAC), which is used to ensure the integrity of the data transmitted over the wireless channel.

The CK is applied in the following scenarios:

  1. User Data Encryption: The CK is used to encrypt the user data before transmitting it over the wireless channel. The UE and the BS use the same CK to ensure that the data can be decrypted by the intended recipient only.
  2. User Data Decryption: The CK is used to decrypt the encrypted user data received from the wireless channel. The UE and the BS use the same CK to ensure that the data can be decrypted by the intended recipient only.
  3. Control Information Encryption: The CK is used to encrypt the control information transmitted between the UE and the BS, such as the radio resource control (RRC) messages. The encryption of the control information ensures that the information cannot be intercepted by an eavesdropper.
  4. Control Information Decryption: The CK is used to decrypt the encrypted control information received from the wireless channel. The decryption of the control information ensures that the intended recipient can understand and act upon the information.
  5. Message Authentication Code (MAC) Generation: The CK is used to generate the message authentication code (MAC), which is appended to the encrypted user data and control information before transmission over the wireless channel. The MAC is used to ensure the integrity of the transmitted data by detecting any changes made to the data during transmission.

In addition to the above applications, the CK is also used for handover procedures, where the UE is handed over from one BS to another BS while maintaining the security and confidentiality of the communication link.

Security Considerations of Ciphering Key (CK):

The security of the Ciphering key (CK) is of utmost importance in the wireless communication networks. If the CK is compromised, an attacker can eavesdrop on the communication link and access sensitive information exchanged between the UE and the BS. To ensure the security of the CK, the following measures are taken:

  1. Use of Strong Encryption Algorithms: The CK is generated using strong encryption algorithms that are resistant to attacks, such as brute-force attacks and dictionary attacks. The 3GPP specifications mandate the use of the Advanced Encryption Standard (AES) with a key size of 128 bits for the generation of the CK.
  2. Use of Strong Authentication Mechanisms: The AKA mechanism used to generate the CK involves strong authentication mechanisms that ensure the authenticity of the AV. The use of strong authentication mechanisms makes it difficult for an attacker to compromise the CK.
  3. Use of Secure Key Storage: The CK is stored securely in the UE and the BS. The UE stores the CK in the subscriber identity module (SIM) card, which is a tamper-resistant device that ensures the security of the stored information. The BS stores the CK in a secure database, which is accessible only to authorized personnel.

Conclusion:

The Ciphering key (CK) is a critical component of the security mechanism used in the wireless communication networks. The CK is used to ensure the confidentiality and integrity of the data exchanged between the UE and the BS. The CK is generated using strong encryption and authentication mechanisms and is stored securely in the UE and the BS. The CK is used in the encryption and decryption of user data and control information, and in the generation of the message authentication code (MAC) to ensure the integrity of the transmitted data. The CK plays a vital role in maintaining the security of the wireless communication networks and ensures that the communication link is not compromised by attackers.