Answers to what people ask most, written by the person who builds ShieldSync.
Getting started
Install ShieldSync on both and choose a folder on each. On the same network they find each other in the Nearby list; accept the pairing on both and the folder starts syncing. No account is needed for this.
Not to sync your own computers on the same network. You need a free account for the cloud: 5 GB of encrypted storage, reaching computers that are far away, and sharing by email.
In ordinary folders on your computer, exactly where you put them. ShieldSync never moves them into a special vault, so they keep working with every other app.
Yes. Make a workspace for each; every workspace has its own folder, sharing and cloud settings.
Syncing
Check that both computers are on and running ShieldSync. On Windows, a firewall can block nearby devices: the app shows "Connection blocked" with a button to repair it. If the other computer is far away, sign in so the change can go through your cloud.
Both versions are kept. The other version is saved beside yours as a conflict copy, so nothing is overwritten and you can merge them yourself.
Yes. Open the transfers list at the top of the app and stop it. The file stays on your computer and nothing already in the cloud is deleted.
Yes. In an item’s sharing settings, pause it for that device. Everything else keeps syncing; resume it from the same place.
Cloud and storage
5 GB on the free plan, 250 GB on Personal and 750 GB on Pro. Syncing between your own computers does not use any of it.
Files that stay in your cloud but still show in File Explorer or Finder with their real names. Open one and it downloads; free up space on a folder and its files go back to online-only. Available on Personal and Pro.
New uploads to the cloud stop until you free space or move up a plan. Nothing is deleted to make room, and syncing between your own computers carries on. The one exception is when your allowance shrinks under files already stored, for example when a paid plan ends: after 30 days and two emails, the most recently added cloud files above the allowance move to your cloud trash, where you can restore them. Files on your own computers are never touched.
Sharing
Right-click it in ShieldSync and choose Share. Invite a person by email, hand it to a device in the same room, or create a guest link.
The other person loses access to new changes. Nothing is deleted from your computer, and they keep the copy they already had.
The key that unlocks a guest link travels after the # in the address, a part browsers never send to a server, so we cannot open what you share. Links can expire, and you can revoke them at any time.
Security and account
No. Files and their names are encrypted on your device before they upload, and the keys never leave it. We see how much space you use and when something changed.
You can set a new password from the sign-in page. Because we never hold your keys, unlocking your encrypted files afterwards needs your recovery code, so keep it somewhere safe.
Yes. Turn on an authenticator app in your account settings; sign-in then asks for its six-digit code.
Billing and plans
Sign in on this website, open your account and choose a plan. Payments are handled by Stripe; we never see your card details.
You go back to the free plan and its 5 GB. Nothing on your computers changes. If your cloud holds more than 5 GB, we warn you and give you time to make room before anything over the limit moves to your cloud’s Deleted bin.
Glossary
The words behind private sync.
Plain explanations of the networking and cryptography terms you will meet around ShieldSync.
AES-256
The Advanced Encryption Standard with a 256-bit key. A symmetric cipher trusted by governments and banks; ShieldSync uses it, in GCM mode, to lock every piece of every file before it leaves your device.
Argon2id
A deliberately slow way of turning a password into a key, so that guessing passwords by brute force takes far too long to be worth it. ShieldSync runs it on your device; your password never leaves it.
Content-defined chunking
Cutting a file into pieces at points chosen by what is inside it rather than at fixed sizes. Change one part of a file and only the pieces around the change are new, so only they need to travel.
End-to-end encryption (E2EE)
Data is encrypted on the sender’s device and only decrypted on the recipient’s. Nothing in between, including the service that carries it, can read it.
Guest link
A link that lets anyone open something you share, in a browser, without an account. In ShieldSync, the key that unlocks it travels after the # in the address, a part browsers never send to a server.
NAT traversal (hole punching)
Techniques for connecting two computers directly when one or both sit behind a router that hides them from the internet.
Online-only file
A file that shows in your file manager with its real name and size, but whose contents stay in the cloud until you open it.
Peer-to-peer (P2P)
Computers talking directly to each other instead of through a central server. ShieldSync syncs your own computers this way whenever it can.
Relay
A server that passes encrypted traffic between two computers that cannot reach each other directly. A ShieldSync relay only ever sees ciphertext.
Version history
Earlier versions of a file, kept so you can bring one back after a mistake.
X25519
A modern way for two parties to agree on a secret key. ShieldSync uses it to hand a shared folder’s key to the person you share with, so only they can open it.
Zero-knowledge architecture
A design in which the service provider stores your data but cannot read it, because only you hold the keys.