How I’m Building a Permanent Blockchain Archive - Part 2

#programming #webdev #blockchain #react

AI Moderation and Sensitive Data Protection

If it’s forever, it better be safe.

In Part 1, I introduced Immutable Notes, a decentralized archive where people can mint messages or personal notes as on-chain SVG NFTs — no IPFS, no servers, no silent failures. The entire visual output is generated in SVG and stored fully on-chain.

But blockchain permanence comes with responsibility.
If you let people write anything to the chain, you risk storing:

NSFW or hateful content

Personally identifiable information (PII) like emails, phone numbers, and passwords

Sensitive data they might later regret putting on a permanent ledger

So in Part 2, I focused on making minting safe by design, using a combination of AI moderation and custom validation logic.

The Moderation Stack
I added a two-layer protection system:

1. OpenAI Moderation API
Before minting, the user’s message is sent to the OpenAI Moderation endpoint, which checks the text for violations like:

Hate or harassment
Sexual or violent content
Self-harm
Criminal activity

It returns a simple flagged: true/false response — fast, accurate, and cheap ($0.002 per 1,000 messages).

2. PII Detection with Regex
OpenAI’s moderation doesn’t catch everything, so I wrote a set of custom filters to block:

Emails: [email protected]
Phone numbers: (555) 123-4567
Card numbers: 4242 4242 4242 4242
Passwords: password=secret123

function containsSensitiveInfo(text: string): string | null {
  const emailRegex = /\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b/i;
  const phoneRegex = /\b(\+?\d{1,3}[-.\s]?)?\(?\d{2,4}\)?[-.\s]?\d{3,5}[-.\s]?\d{4}\b/;
  const cardRegex = /\b(?:\d[ -]*?){13,16}\b/;
  const passwordRegex = /(?:password|passwd|pass)\s*[:=]\s*\S+/i;

  if (emailRegex.test(text)) return "email address";
  if (phoneRegex.test(text)) return "phone number";
  if (cardRegex.test(text)) return "credit card number";
  if (passwordRegex.test(text)) return "password";

  return null;
}

If any of those patterns are detected, the user gets an alert and can’t proceed to minting.

Sample Workflow
The user types their message into the NftSvgEditor.

On “Submit”, the app:

Runs PII checks
Sends the message to /api/moderate
Receives moderation response from OpenAI

If the message is flagged or contains PII, the app shows a helpful alert and blocks minting.

Built With

Next.js 15.3.5 App Router (Edge-ready)
React 19 with server/client components
OpenAI Moderation API
Regex-based validation for common PII patterns
Custom Alert component for UX feedback

Why It Matters
I believe blockchain permanence requires thoughtful constraints. Immutable Notes isn't just a place to write — it’s a place to preserve something that should be preserved.

Letting harmful, illegal, or personal data into the system would contradict that mission, so these safeguards are essential.

Coming in Part 3…
Next up, I’ll show how I’m: