What is the focus of PCI DSS Requirement 4?

The correct focus of PCI DSS Requirement 4 is on encrypting the transmission of cardholder data across open and public networks. This requirement is crucial because cardholder data can be intercepted as it travels through less secure environments, posing a significant risk to the privacy and security of the data. Encryption serves as a protective measure to ensure that even if the data is intercepted, it cannot be easily read or misused by unauthorized individuals.

In line with the requirements of PCI DSS, organizations must implement strong cryptography and security protocols to safeguard cardholder data during transmission over any network that is not secure. This is an essential component in preventing data breaches and maintaining compliance with PCI DSS standards, which are designed to protect sensitive payment card information.

The other options do not directly address this specific requirement. Encrypting remote access to internal systems has its own requirements under PCI DSS but does not encompass the broader context of protecting cardholder data during transmission. Keeping all cardholder data in one location does not relate to the encryption of data in transit, and storing data on unsecured messages is contrary to the goals of PCI DSS, which seeks to enhance data security rather than compromise it.