Frequently Asked Questions about Sicher

General

Sending messages

Mobile app

General

What is 'Sicher'?

Sicher is an old German word with a meaning of ‘safe, secure, certain’. It’s also a name of a great messenger you can rely on.

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Why is Sicher secure? What exactly does it mean?

Sicher is based on several concepts ensuring your data is safe: Encryption, Access Control, Lifetime Control. Encryption means nobody (including us!) except the original recipient can read the message. Access Control protects your data even if your phone has been stolen. With Lifetime Control you can make your messages self-destruct with no traces left.

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Why should I trust you?

Sicher is developed by SHAPE GmbH, a Stuttgart-based company founded in 1999. We are developing mobile messaging apps since 2002. More than 30 million people have used our apps on 15+ mobile platforms. We believe our experience and credibility speak for itself.

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Why do you need my phone number?

Phone number is a convenient unique identifier that can easily be confirmed. It saves us from spammers. It is also very efficient in finding people who are already using the service, since we usually already have big address books - that is, big lists of existing and potential Sicher contacts.

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Sending messages

How can I be sure my messages are sent securely?

Sicher is using point-to-point encryption, based on asymmetric cryptography. It means that only the recipient who owns the private key can decrypt the message. RSA cryptosystem is used with 2048 bit keys. Additionally all data exchange between mobile apps and Sicher servers is protected using SSL.

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Are pictures, voice messages and files also encrypted?

Yes. Asymmetric ciphers are not well suitable to encrypt big files, so prior to sending all files are encrypted with symmetric AES cipher. One-time-password for this symmetrical encryption is sent as a message in Sicher, which means it is itself encrypted with RSA. Sending files means temporarily uploading them to Sicher server, so the recipient can download them later. Note only recipient has the key to decrypt the files and key lifetime is chosen by the sender.

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What if I receive a push notification about new message. Will it be shown on my lock screen?

No. If Sicher is not the active running application, you will only see a notification about a new message, not showing its text. You will have to open Sicher to read the message.

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Do you keep my messages on your servers?

No. Messages are only kept in memory until they are delivered, and immediately deleted after that. All messages awaiting delivery are encrypted by recipient’s public key, so we can’t read them.

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Is my address book stored on your servers?

No. Sicher periodically synchronizes your address book with its servers to find your contacts who have joined the service. It means sending contact names and phone numbers to server, where they are matched against existing service users. This data is not stored on servers. Only matching contacts are added to your contact list, all other data is discarded.

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Mobile app

What about messages and files on my phone? Are they encrypted?

On mobile devices all messages, received files and metadata are encrypted before saving them to internal storage. These items are decrypted in memory only when app needs to present them to a user. Items can be temporarily saved to a local storage upon opening them in another application.
Application passcode is used as a key to symmetric AES encryption, protecting locally saved data. Anyone who gets access to your mobile device will not be able to decrypt stored messages and files unless he/she knows the passcode. That’s why it is very important to set and remember your passcode. If you forget it, there’s no way of recovering your data.

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What if I left the phone on my desk, can anyone read my messages?

No. You can set application-level passcode with a minimum timeout of two minutes. It means the app will lock itself and ask for a passcode if left for two minutes or more. Additionally we highly recommend setting a device-level passcode or fingerprint lock on iOS, which really boosts the level of security. On Apple devices it also turns on an additional hardware encryption.

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What is 'self-destruction'? How does it work?

If you set a self-destruction timer for your messages, they will be automatically deleted after timer expires. Messages are deleted both on sender’s and receiver’s side. You will have no traces left about your communication. Self-destruction timer is local for each user. For sender it starts ticking right after sending the message, for each recipient it starts after the message is displayed.

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I've sent or received something really private. I don't want to wait for a self-destruction timer, I want to have this message gone NOW!

Tap 'Delete Chat Now' in a dialog menu. It immediately removes all messages for all participants. You and your contacts will never see these messages again.

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How can I create group chats?

Open a dialog with the first group chat participant, then choose ‘Invite’ from dialog menu.

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Is a group chat as secure as one-to-one?

Yes. Sending a message to group chat actually means sending as many messages as there are group chat participants. Each message is encrypted with its’ recipient public key.

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I've signed up to the service, but by contact list is empty. What's next?

It means that none of your phone book contacts is signed up with Sicher. Take a moment to invite them using the built-in ‘Invite Friends’ feature. They will appear in your list automatically as soon as they join the service.

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I have uninstalled Sicher but my friends still see me in their apps. How to sign out completely?

Install Sicher again, log in with your phone number, then open Account page and select 'Remove Account'. After that you can uninstall the app.

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I really want Sicher to be quiet and not send me any push notifications. How do I turn it off?

Please turn off push notifications for Sicher in system settings for your device. There’s no application-level setting for this.

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I want to install Sicher on multiple phones.

Currently a Sicher ID can only be active on one mobile device.

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I've lost my passcode for Sicher and can’t open the app. What should I do?

There's no way to recover your passcode. Uninstall Sicher, then install it again and register with your phone number. You'll have your contact list back, but no chats.

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