🔐 How Should PCI Data Be Stored in the Database?

Best Practices for Developers, Architects, and Anyone Who Doesn’t Want to End Up in the News

If you're handling credit card data, you're sitting on a vault of highly sensitive information. That means you’re also on the hook for protecting it — not just from attackers, but from sloppy internal practices. Welcome to the world of PCI DSS (Payment Card Industry Data Security Standard), the global rulebook for keeping cardholder data safe.

One of the most common questions I hear from engineers and tech leads is:

How should PCI data be stored in a database, and what are the best practices for transit and encryption?

Let’s break it down — simply, practically, and without buzzwords.

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🚫 First Rule: Don’t Store PCI Data Unless You Absolutely Have To

Seriously. If you can get away without storing cardholder data (especially full PANs — Primary Account Numbers), that’s your best option. Use tokenization, third-party vaults, or payment gateways that keep you out of PCI scope.

But if you must store it, here’s how to do it right.

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1. 🔄 Encrypt Data in Transit

Any time cardholder data is moving — from a browser to your backend, or between internal services — it needs to be encrypted using strong transport encryption like:

• TLS 1.2 or above

• Mutual TLS (mTLS) for internal service-to-service calls

✅ Avoid outdated protocols like SSL, TLS 1.0, or 1.1.

Example:
A user submits their card on your checkout form. That request must be protected using HTTPS (TLS 1.2+). If you’re passing it to a payment processor or another service, that connection needs encryption too.

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2. 💾 Encrypt Data at Rest (Strongly)

If you’re storing cardholder data:

• Use AES-256 or AES-128-GCM

• Store encryption keys separately, with hardened access policies

• Never store CVV/CVC after authorization (PCI considers this a violation)

PCI DSS also expects:

• Proper key rotation procedures

• Access logs and audit trails

• Fine-grained access control (least privilege)

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3. ⏱️ Decrypt Only When Needed — and Only in Memory

You might need to decrypt a PAN to send it to a processor or run a fraud check — and that’s fine. But:

• Decryption should only happen in-memory

• Never write decrypted data to disk or logs

• Keep the decrypted data’s lifetime as short as possible

Treat decryption like a scalpel, not a hammer.

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4. 👀 Mask When Displaying

If cardholder data needs to be shown — say, to a support agent or the user — only display the last 4 digits. Never show the full PAN, CVV, or expiration date together.

Example: **** **** **** 1234

This helps avoid accidental exposure while still providing recognizable info to the user.

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5. ❌ Don’t DIY Crypto

Rolling your own encryption is like writing your own seatbelt. It might seem secure until you crash.

Instead, use:

• AWS KMS, Azure Key Vault, or a dedicated HSM

• Well-tested crypto libraries like OpenSSL, Bouncy Castle, or libsodium

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🤔 Wait, What About Hashing?

Good question — but hashing is not appropriate for storing PANs. Hashing is one-way, meaning you can’t recover the original card number. PCI requires that PANs be encrypted (i.e., reversible, with controlled access) — not hashed.

That said, hashing can be used for:

• Internal indexing or deduplication

• Anonymized analytics or fraud detection

But for secure storage? Encryption is the only acceptable option.

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🧠 Final Thoughts

PCI compliance isn’t a checklist. It’s a security posture. If you're encrypting in transit, encrypting at rest, avoiding unnecessary storage, and applying access control with discipline — you're on the right path.

But here’s the truth nobody likes to say out loud:

The safest PCI data is the one you never store.

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