How Is Cardholder Data Protected at Rest and in Transit Under PCI-DSS?

When customers submit their card details online or swipe a card at a terminal, they expect one thing: to keep payment data safe. Behind the scenes, that trust depends heavily on how companies protect cardholder data, both when it is stored and when it is moving across networks.

This is why PCI-DSS places such strong emphasis on encryption, tokenization, and secure transport protocols. Protecting cardholder data at rest and in transit is not just a technical requirement; it is a fundamental security expectation.

Payment data is a primary target for attackers. A single exposed card number can lead to fraud, chargebacks, regulatory penalties, and reputation damage. PCI-DSS recognizes the risk and assumes that systems may ultimately be breached.

The aim is simple: even if attackers gain access, the data should be useless.

That is why PCI-DSS does not depend on a single control. Instead, it layers protections covering cardholder data wherever it subsists on disks, in databases, in backups, and while traveling between systems.

Protecting Cardholder Data at Rest

Data “at rest” signifies cardholder data stored in databases, files, backups, or logs. PCI-DSS Requirement 3 focuses specifically on this area.

1. Minimize Data Storage

The safest card data is the one you don’t store at all. PCI-DSS encourages companies to:

• Avoid storage of full Primary Account Numbers (PANs)
• Remove unnecessary information
• Define and implement data retention limits

Many organizations reduce risk significantly by outsourcing storage to PCI-compliant payment processors.

2. Applying Cryptography for Stored Data

When cardholder data needs to be stored, PCI-DSS requires it to be protected using strong cryptography.

This means:

• Using industry-based and accepted algorithms (such as AES-256)
• Making sure encryption keys are protected and managed safely
• Encrypting databases, file systems, and backups that can contain card data

An encryption implementation that, even if attackers access the storage layer, the data can be unreadable without the keys.

3. Key Management is very Important as Encryption

Encryption without good key management is useless. PCI-DSS expects companies to:

• Restricting access to encryption keys
• Need to store keys separately from encrypted data
• Rotate keys regularly
• Revoke keys when compromised or when they are no longer needed

Auditors often focus on key management because weak key handling can weaken otherwise strong encryption.

4. Use of Tokenization as an Extra Layer of Protection

Tokenization will replace sensitive card data with non-sensitive data called a token. The original data is stored securely, often by a payment provider.

Benefits of tokenization:

• Reduced PCI scope
• Lower breach impact
• Use of data safely in internal systems

In many modern-day environments, tokenization is preferred over encryption for operational systems because it prevents direct exposure to card data.

Data “in transit” refers to cardholder data moving between systems, such as from a customer’s browser to a payment gateway, or between internal services. PCI-DSS Requirement 4 addresses this area.

1. Encrypt During Transmission

PCI-DSS requires that cardholder data be encrypted whenever it is transmitted over open or public networks.

This includes:

• Internet traffic
• Wireless networks
• External connections between systems

TLS is the common method to prevent interception and tampering.

2. Using only Secure Transport Protocols

PCI-DSS explicitly prohibits outdated and insecure protocols.

Companies must include:

• Implementing modern TLS versions
• Disabling weak encryptions
• Reviewing protocol configurations

Even encrypted traffic can be vulnerable if outdated algorithms are used.

3. Internal Traffic Matters Too

A misconception is that only external traffic needs encryption. PCI-DSS is clear that internal transmissions involving cardholder data must be protected, especially when systems are segmented across networks.

Encrypting internal data flows helps prevent lateral movement if attackers gain a foothold.

4. Securing Remote Access

Remote access to environments that are handling cardholder data must be controlled.

PCI-DSS requires:

• Encrypted connections (VPN or secure gateways)
• Strong authentication, which is multi-factor authentication (MFA)
• Monitoring and logging of remote sessions

Unsecured remote access remains one of the common PCI compliance failures.

Encryption and secure transport need to be regularly monitored and validated.

Companies must:

• Regularly test encryption configurations
• Review certificates and the date of expiration
• Continuous monitoring of logs for suspicious access or transmission attempts
• Include encryption checks in vulnerability scans and penetration tests

Auditors do not just want to know that encryption exists; they want evidence that it is working and implemented.

Companies with good intentions can introduce risk vulnerabilities. Regular issues include:

• Storing card data to increase exposure without a business justification
• Using Weak and poorly protected encryption keys
• Encrypting external traffic but neglecting internal flows
• Using outdated TLS versions
• Unreliable encryption across environments

These gaps often come to light during audits, or worse, after an incident.

PCI-DSS requirements for protecting cardholder data at rest and in transit are grounded in real‑world threats and proven risk‑reduction practices.

When cryptography, tokenization, and secure transport protocols are implemented effectively, they make sure that cardholder data remains secure during breaches.

For companies, this is not just about passing PCI audits. It is about protecting customers, reducing fraud risk, and maintaining trust in an increasingly aggressive digital environment.

If your company processes payment data, reviewing how cardholder data is stored, encrypted, transmitted, and monitored is one of the most impactful steps any company can take to strengthen its security today and every day after.

Protecting cardholder data under PCI-DSS requires more than enabling encryption; it demands a structured approach to how data is stored, transmitted, and controlled across systems. Azpirantz helps organizations implement practical data protection strategies, from minimizing storage and applying strong cryptography to designing secure key management and tokenization frameworks. On the transmission side, we ensure secure protocol implementation, encrypted internal and external data flows, and controlled remote access. The focus is on aligning PCI-DSS requirements with real infrastructure, ensuring controls are not only in place but consistently enforced and auditable. With Azpirantz, organizations build a data protection approach that reduces exposure, strengthens trust, and stands up to PCI assessments.

*This content has been created and published by the Azpirantz Marketing Team and should not be considered as professional advice. For expert consulting and professional advice, please reach out to [email protected].