shred

A free, open-source, zero-knowledge ephemeral file-sharing service. Files are encrypted in the browser before they're uploaded — the server never sees your file contents, filenames, keys, or passwords. Share a link, the recipient downloads and decrypts, and the file deletes itself on expiry or after download.

How it works

• Client-side encryption. Files are encrypted with AES-256-GCM in the browser (chunked, 1 MiB per chunk). The random key is put in the URL fragment (#k=…), which never reaches the server — the link is the key.
• Encrypted filenames. The filename is encrypted under the same key, so the server only ever stores opaque ciphertext.
• Password mode (optional). Instead of putting the key in the link, derive it from a passphrase (PBKDF2, 600k iterations, SHA-256) and wrap the content key with AES-KW. Leave the passphrase blank to auto-generate a 5-word Diceware one (~64 bits, from a CSPRNG).
• Metadata stripping. Images are re-encoded via canvas to drop EXIF/GPS.
• Ephemeral by default. Pick 1 hour / 1 day / 1 week, or burn-after-reading. Expired files are cleaned up automatically; nothing is kept longer than its TTL.

Stack

Flask + vanilla JS, SQLite for metadata, files sharded on disk. Runs under gunicorn behind nginx or Caddy. No accounts, no third-party services, no client-side dependencies to load.

Running it

python3 -m venv venv && source venv/bin/activate
pip install -r requirements.txt 
cp .env.example .env       # edit as needed, please read!!
python server.py            # dev server on http://127.0.0.1:5000

For production, run under gunicorn behind a TLS-terminating reverse proxy:

gunicorn --workers 1 --bind 127.0.0.1:8000 --timeout 3600 server:app

Example nginx, Caddy, and systemd configs are in deploy/. Set TRUSTED_PROXY_COUNT=1 so the app sees the real client IP behind the proxy.

systemd

Drop deploy/shred.service into /etc/systemd/system/, adjust the WorkingDirectory and EnvironmentFile paths, then:

sudo systemctl daemon-reload
sudo systemctl enable --now shred

Configuration

All settings are environment variables (loaded from .env); see .env.example for the full list. The ones worth knowing:

Variable	Purpose
STORAGE_DIR	Where the database and uploads live (default data).
MAX_SIZE_BYTES	Per-file size cap (default 2 GB).
MIN_FREE_DISK_BYTES	Stop accepting uploads below this much free space (default 1 GB).
TRUSTED_PROXY_COUNT	Trusted reverse-proxy hops. Set to 1 behind nginx/Caddy.
ABUSE_CONTACT	Address shown on the /terms page.
UPLOAD_TOKEN	Static secret required to upload.
UPLOAD_IP_ALLOWLIST	Comma-separated IPs/CIDRs allowed to upload.
UPLOAD_TOKEN_ROTATION	Rotate the upload token every N seconds (0 = off).
ADMIN_TOKEN	Secret for the admin panel and token API.

Upload gating

By default anyone can upload. For a private instance (e.g. sharing with friends), gate uploads — this is the single biggest thing that reduces abuse exposure. Downloads are never gated, since the link itself is the decryption key.

• Static token — set UPLOAD_TOKEN; the upload page then asks for it.
• IP allowlist — set UPLOAD_IP_ALLOWLIST.
• Rotating tokens — set UPLOAD_TOKEN_ROTATION to mint a fresh token every N seconds; a leaked token stops working within 2×N. Fetch the current one from the admin panel or GET /api/admin/token.

Admin panel

/admin, unlocked with ADMIN_TOKEN. Shows an overview (uptime, storage, disk usage, counts), the current upload token (reveal / rotate), the list of stored files (metadata only — never plaintext), and the abuse-report queue. From here you can pause, restore, or delete any file.

Abuse handling

Every file's download page has a report button. Reporting pauses the file immediately — downloads are blocked and the page shows "reported, pending review" — without the operator ever decrypting anything. Reported files land in the admin queue, where you review them and either restore or delete. Takedown and law-enforcement contact is on the /terms page.

Wiping data

To permanently delete all uploaded files and the database:

./scripts/wipe.sh          # prompts for confirmation
./scripts/wipe.sh --yes    # no prompt

Your .env and ADMIN_TOKEN are left alone; an empty database is recreated on the next start.

Security notes

• Everything sensitive is encrypted client-side; the server is zero-knowledge by design. It cannot read, search, or recover file contents.
• Strict CSP (no inline scripts/styles), COOP/COEP/CORP, nosniff, X-Frame-Options: DENY, and HSTS when served over TLS.
• File IDs are validated against a strict pattern and paths are contained to the upload directory, so IDs can't be used for traversal.
• Client-side encryption protects your users' privacy; it does not shield the operator from legal responsibility for hosted content. If you run a public instance, read /terms, set a real ABUSE_CONTACT, and understand your jurisdiction's obligations.

License

Licensed under the GNU Affero General Public License v3.0 (AGPL-3.0). See LICENSE for the full text.

Copyright (C) 2026 btea.dev

This program is free software: you can redistribute it and/or modify it
under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
for more details.

You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.