In a public key infrastructure, which key is responsible for decrypting the data?

In a public key infrastructure (PKI), the private key is crucial for decrypting data that has been encrypted with the corresponding public key. This system relies on asymmetric cryptography, where two keys are used: one public and one private.

When a sender encrypts data using the recipient's public key, only the recipient’s private key can decrypt that data. This ensures that only the intended recipient, who possesses the private key, can access the original information. The separation of keys provides a higher level of security, as the private key is kept confidential and never shared, while the public key can be distributed openly.

The other types of keys mentioned are used in different contexts. The public key is used for encrypting the data, the master key is often associated with symmetric key encryption for session management, and a shared key refers to a symmetric key that is known to both parties for encryption and decryption processes. These do not play the role of decrypting data in the context of a PKI system. Thus, understanding the function of the private key is essential for grasping how secure communications are established using public key infrastructure.