paaster

End-to-end encrypted text and file sharing platform.
Content is encrypted in your browser before upload — the server never sees the plaintext or the key.

Features

• End-to-end encryption — text and files are encrypted client-side with AES-128-GCM via the Web Crypto API. The decryption key lives only in the URL fragment (#...), which browsers never send to the server.
• Code editor with syntax highlighting — CodeMirror 6 with support for 17 languages (Markdown, Python, JavaScript/TypeScript, Java, SQL, HTML, CSS, C/C++, Go, PHP, Rust, JSON, YAML, XML, and plain text).
• File attachments — share multiple encrypted files alongside (or instead of) text. File count and total size limits are configurable.
• Flexible expiration — 10/30 minutes, 1/6/12 hours, 1/3/7 days, or burn after read (deleted the moment it's first viewed).
• Optional password protection — a 6–12 character password is mixed into the encryption parameters client-side, so even someone with the link can't decrypt without it.
• QR code sharing — instantly share a paste with another device.
• Pluggable storage — attachments go to Vercel Blob or Cloudflare R2; metadata and ciphertext live in Redis with native TTL expiry.
• Automatic cleanup — a daily cron job removes expired attachment files from storage.
• Dark / light theme — follows your system preference, toggleable.

How the encryption works

1. When you publish, the browser generates a random AES-128-GCM key and a 12-byte IV.

2. Text and attachments are encrypted locally; only ciphertext is uploaded.

3. The key + IV are base62-encoded into a URL fragment, producing a link like:

   https://your-domain.com/Ab3xYz#3fK9...38-char-fragment...
   

4. The fragment (#...) is never included in HTTP requests, so the server stores ciphertext it cannot decrypt.

5. If a password is set, it is folded into the IV derivation client-side — the password itself is never transmitted; the server only stores a hasPassword flag.

6. For burn-after-read pastes, the record is deleted atomically on first fetch (a Redis lock prevents double reads), and any attachments are queued for deletion shortly after.

Tech stack

Layer	Technology
Framework	Next.js 15 (App Router, Turbopack) + React 19
Styling	Tailwind CSS 4, shadcn/ui (Radix UI)
Editor	CodeMirror 6
Data store	Upstash Redis
File storage	Vercel Blob or Cloudflare R2
Encryption	Web Crypto API (AES-128-GCM)

Getting started

Prerequisites

• Node.js 20+
• pnpm
• An Upstash Redis database
• A Vercel Blob store or a Cloudflare R2 bucket

Setup

git clone https://github.com/<your-username>/paaster.git
cd paaster
pnpm install

cp .env.example .env.local
# fill in .env.local (see configuration below)

pnpm dev

Open http://localhost:3000.

Configuration

All settings live in .env.local (see .env.example for the full annotated template).

Redis (required)

Variable	Description
KV_REST_API_URL	Upstash Redis REST URL
KV_REST_API_TOKEN	Upstash Redis REST token

Storage backend

Variable	Description
STORAGE_PROVIDER	vercel (default) or r2
UPLOAD_PATH	Object key prefix for uploaded files (default paaster)

Vercel Blob (STORAGE_PROVIDER=vercel):

Variable	Description
BLOB_READ_WRITE_TOKEN	Vercel Blob read-write token

Cloudflare R2 (STORAGE_PROVIDER=r2):

Variable	Description
R2_ACCOUNT_ID	Cloudflare account ID
R2_ACCESS_KEY_ID / R2_SECRET_ACCESS_KEY	R2 API credentials
R2_BUCKET	Bucket name (must allow public read access)
R2_PUBLIC_URL	Public bucket URL (https://pub-xxxx.r2.dev) or a custom domain

Important

R2_PUBLIC_URL must map to the bucket root with no path segment (e.g. https://files.example.com, not https://files.example.com/cdn). File cleanup derives the object key from the URL path and would otherwise silently leave expired files in the bucket.

Upload limits

Variable	Default	Description
NEXT_PUBLIC_MAX_FILE_COUNT	10	Max attachments per paste
NEXT_PUBLIC_MAX_TOTAL_SIZE_MB	50	Max total attachment size (MB)

Cron

Variable	Description
CRON_SECRET	Bearer token required to call GET /api/cron (expired-file cleanup)

Deployment

The app is designed for Vercel: connect the repository, set the environment variables above, and deploy. The included vercel.json schedules the cleanup cron daily at 01:00 UTC (Vercel sends CRON_SECRET automatically as the bearer token).

If you host elsewhere, schedule the cleanup yourself:

curl -H "Authorization: Bearer $CRON_SECRET" https://your-domain.com/api/cron

API

Method	Endpoint	Description
POST	/api	Create a paste (multipart form: encrypted text/files, format, expiry, flags)
GET	/api/:id	Fetch a paste's encrypted content (deletes it if burn-after-read)
GET	/api/cron	Delete expired attachment files (requires CRON_SECRET)

All content in these payloads is ciphertext; decryption happens in the browser using the URL fragment.

Project structure

app/
  page.tsx           # Home: editor, attachments, expiry/password options
  [id]/page.tsx      # Paste viewer: fetches ciphertext and decrypts client-side
  api/route.ts       # POST  /api      — create paste
  api/[id]/route.ts  # GET   /api/:id  — fetch paste (burn-after-read handling)
  api/cron/route.ts  # GET   /api/cron — expired-file cleanup
components/          # Editor, header/footer, QR code, shadcn/ui primitives
lib/
  crypto.ts          # Client-side AES-GCM encrypt/decrypt + URL fragment codec
  storage/           # Storage abstraction: Vercel Blob & Cloudflare R2 backends
  redis.ts           # Upstash Redis client
  config.ts          # Upload limit configuration

Development

pnpm dev        # start dev server (Turbopack)
pnpm build      # production build
pnpm start      # serve production build
pnpm lint       # lint
pnpm lint:fix   # lint and auto-fix

License

MIT