Frequently Asked Questions

1. Visit Undercover Drop and drag your file onto the drop zone, or click to browse.
2. Enter a password — this is your only encryption key. Choose something strong and memorable. We recommend 12+ characters.
3. Click Encrypt. Your browser encrypts the file using AES-256-GCM with your password — nothing is sent to any server at this point.
4. Once encrypted, the file is uploaded to our server as an opaque blob. You'll receive a unique shareable link.
5. Copy the link and share it with your recipient along with the password (via a separate channel — email, Signal, etc.).

Important: If you lose your password, there is no recovery. We don't store it anywhere — that's the point of zero-knowledge encryption.

1. Encrypt your file (see above). After encryption you'll land on a download page with a unique URL.
2. Copy the link from your browser's address bar or the on-screen copy button.
3. Send the link to your recipient through any messaging platform. The link is safe to share publicly.
4. Separately, send them the password — ideally through a different channel (e.g., link by SMS, password by Signal). Sharing both over the same channel reduces security.
5. Optionally, set a download limit or expiry time before encrypting to control who can access the file and for how long.

Files are stored as encrypted blobs. Anyone with the link and the password can decrypt and download the file.

The download limit counts each time the encrypted file is fetched from our servers — not successful decryptions.

Because all decryption happens in your browser, we never see your passphrase and can't tell whether a download actually succeeded. So an opened link counts even if the recipient typed the wrong passphrase. Retrying the passphrase on the same page does not count again — the file is fetched once and reused.

When the limit is reached, the link is automatically made private. The owner is emailed and can delete the file, raise the limit, or reset the count from their dashboard.

1. Open the shared link in your browser. You'll see the Undercover Drop download page showing the file name and size.
2. Enter the password the sender shared with you.
3. Click Decrypt & Download. The file is decrypted entirely in your browser using AES-256-GCM.
4. The decrypted file is then saved to your device — it never passes through our servers in plaintext.

If decryption fails (wrong password), you will see an error. The download will not proceed. There is no server-side attempt to decrypt — all verification is local.

Only the encrypted blob is stored on our servers. Here is exactly what we store and what we don't:

• We store: The encrypted binary blob, the original filename, file size, your email (if you have an account), download limits and expiry settings you configured.
• We do NOT store: Your password, your decryption key, the unencrypted file contents, or any ability to decrypt your data.

This is what "zero-knowledge" means in practice: the server is a dumb store. It holds ciphertext and metadata only. Without your password, the data is unreadable — not just hard to read, but mathematically impossible for us to access.

No. File-type policy checks and blind-hash matching run in the browser and are advisory moderation signals, not server-side inspection.

A custom or modified client can omit or forge those values. Because the server receives ciphertext and cannot inspect plaintext content, these controls must not be relied on as a guarantee that an upload complies with policy.

Both features are optional and set at encrypt time:

• Download limit: Set a maximum number of times the file can be downloaded. Once reached, the link is permanently disabled. This is tracked server-side and cannot be bypassed by clearing cookies or using a different browser.
• Expiry time: Set a date and time after which the link stops working. Expired links show a clear "Link expired" message. Expiry is enforced server-side.
• No expiry / no limit: By default, links work indefinitely with unlimited downloads. You can always delete a file manually from your dashboard.

Both settings can be configured in the advanced options panel before encrypting, and adjusted later from your dashboard for files you uploaded.

Yes. Undercover Drop uses a security architecture designed around verified, open-source cryptographic standards:

• AES-256-GCM — NIST-approved authenticated encryption. Used by governments, banks, and security-critical systems worldwide.
• Argon2id key derivation (64 MiB memory, 3 passes) with a unique random salt per file — a memory-hard function that makes large-scale brute-force attacks far slower and more expensive than older hash-based methods.
• Web Crypto API — Undercover Drop's encryption runs in your browser using the browser's native, audited cryptographic library. No custom crypto.
• Authenticated decryption — GCM's built-in authentication means a tampered ciphertext will always be rejected. You cannot be tricked into accepting a modified file.
• Fresh random IV — Every encryption gets a unique initialization vector, preventing pattern analysis across multiple encrypted files.

What we store: only the encrypted file (ciphertext) and minimal metadata (creation time, expiry, download limit). What we never see or store: your passphrase or your encryption key — all encryption and decryption happen entirely in your browser. A direct consequence: we cannot recover your file if you lose the passphrase, and we cannot decrypt it for anyone, including ourselves or in response to a legal request.

Because we can't see your passphrase, your passphrase is your security. If someone obtains the encrypted file — for example, if a share link reaches the wrong person — they can try to guess the passphrase offline. A weak or common passphrase (e.g. password123) can be cracked; a strong one is effectively impossible.

We slow attackers down with memory-hard Argon2id and a unique salt per file, but no system can rescue a truly weak passphrase. Use the Generate strong passphrase button (or a 4–5 word phrase), and always send the passphrase through a different channel than the link.

We believe privacy is a right, not a feature. Here's what we collect and why:

For the full legal text, see our Privacy Policy. This summary is informational, not legal advice.