- Co je Delta Chat?
  - Jak najít lidi k hovoru?
  - Jaké výhody má Delta Chat vzhledem k ostatním četovacím systémům?
  - Jaké zprávy Delta Chat zobrazuje?
  - What if I expect a message from someone I didn’t write to in the past?
  - Podporuje Delta Chat obrázky, videa a jiné přílohy?
  - How can I add or switch between multiple accounts?
  - Kdo uvidí můj profilový obrázek?
  - Umí Delta Chat pracovat s e-maily v HTML?
  - Proč musím Delta Chatu zadat mé e-mailové heslo? Je to bezpečné?
  - Jaká oprávnění Delta Chat potřebuje?
  - What means Pinning, Muting, Archiving?
  - What does the green dot mean?
  - How do disappearing messages work?
  - How can I delete my account?
- Skupiny
  - Vytvoření skupiny
  - Přidat členy skupiny
  - Kdyź se nedopatřením odstraníš.
  - Nechci již přijímat zprávy ze skupiny.
  - What do the ticks shown beside outgoing messages mean?
  - What happens if I turn on “Delete old messages from server”?
  - What happens if I turn on “Delete old messages from device”?
- Encryption and Security
  - Which standards are used for end-to-end encryption?
  - How can i know if messages are end-to-end encrypted?
  - How can I get guaranteed end-to-end encryption and green checkmarks?
  - What does the green checkmark and “guaranteed end-to-end encryption” mean?
  - A contact “sent a message from another device”, what can i do?
  - Are attachments (pictures, files, audio etc.) end-to-end encrypted?
  - Is OpenPGP secure?
  - Did you consider using alternatives to OpenPGP for end-to-end -encryption?
  - Is Delta Chat vulnerable to EFAIL?
  - Is a message exposed in cleartext if end-to-end encryption is not available?
  - How does Delta Chat protect metadata in messages?
  - How to protect metadata and contacts when a device is seized?
  - How can i check encryption information?
  - How can I check the encryption status of messages?
  - Why do I see unencrypted messages?
  - How can i get an end-to-end encrypted chat with a Delta Chat contact who sometimes uses webmail or another non-Autocrypt e-mail app?
  - How can I ensure message end-to-end encryption and deletion?
  - Does Delta Chat support Perfect Forward Secrecy?
  - Is end-to-end encryption of Delta Chat as safe as Signal?
  - Lze znovu použít můj stávající soukromý klíč?
  - Nemohu do Delta Chatu zavést můj stávající PGP klíč.
- Více klientů najednou
  - Lze Delta Chat používat souběžně na více zařízeních?
  - Troubleshooting
  - Manual Transfer
  - Je v plánu vytvořit webovou verzi Delta Chatu?
  - K čemu je dobré nastavení “Posílat si kopii”?
  - Proč můžu nastavit sledování složky Odeslané?
  - Proč mohu zvolit nesledovat složku DeltaChat?
- webxdc apps
  - How private are webxdc apps?
  - Where can I get webxdc apps?
  - How can I create my own webxdc apps?
- Experimental Features
  - How can I use audio/video calls with Delta Chat?
  - What are Broadcast Lists and how can I use them?
  - How can I share my location with my chat partners?
  - What does the experimental database encryption actually protect?
  - Why can I choose to only watch the DeltaChat folder?
  - How can I change my account to a different e-mail address?
- Různé
  - Pracuje Delta Chat s mým poskytovatelem e-mailu?
  - I want to manage my own e-mail server for Delta Chat. What do you recommend?
  - Je hovor v Delta Chatu skutečně interaktivní, když užívá E-Mail?
  - Lze Delta Chat používat s Protonmail / Tutanota / Criptext?
  - Mám zájem o technické podrobnosti. Kde najdu víc?
  - Was Delta Chat independently audited for security vulnerabilities?
  - Jak je financován vývoj Delta Chatu?

## Co je Delta Chat?

Delta Chat je nový četovací messenger, který posílá zprávy přes e-mail, pokud možno zašifrované metodou Autocrypt. Netřeba žádného nového účtu. Pro Delta Chat prostě použijete ten, který už máte pro svůj e-mail.

### Jak najít lidi k hovoru?

Delta Chatem můžete napsat na jakýkoli e-mail i v případě, že příjemce Delta Chat nepoužívá. Není nutné aby příjemce instaloval stejnou aplikaci jako vy, jak vyžadují ostatní četovací systémy.

### Jaké výhody má Delta Chat vzhledem k ostatním četovacím systémům?

- Independent of any company or services. You own your data.
- Your data is not saved on a central server unless all users are using the same e-mail servers
- You do not distribute your address book to anyone.
- Fast by the use of Push-IMAP.
- Largest userbase - recipients not using Delta Chat can be reached as well.
- No Spam - only messages of known users are shown by default.
- End-to-end encryption via Autocrypt.
- Copyleft and Standards based libre software.
- Flexible identity with built-in support for multiple accounts

### Jaké zprávy Delta Chat zobrazuje?

By default, Delta Chat shows all e-mails.

At “Settings -> Chats & Media -> Show Classic E-Mails”, you can change this. You have these options:

- “No, chats only”: Only messages sent by other Delta Chat users and replies to your Delta Chat messages are shown. This makes most sense if you use the same e-mail account for normal e-mails as well.
- “All”: Delta Chat shows all e-mails that are sent to your email address. This makes sense if you want to use Delta Chat for all your e-mails, so no message gets lost. This is the default setting.
- “For accepted contacts”: Delta Chat shows all e-mails from contacts with whom you already have a chat, but new chats only pop up for Delta Chat messages. This helps to decide on a case-by-case basis whether you want to have a conversation in Delta Chat or in a “normal” e-mail app.

### What if I expect a message from someone I didn’t write to in the past?

- If a message comes from an unknown contact, it appears as a request. You need to accept the request before you can reply.
- You can also “delete” it if you don’t want to chat with them for now. This does not delete the message on the server, only on your device. So you can still deal with the message in a different mail app.
- If you delete a request, future messages from that contact will still appear as message request, so you can change your mind. If you really don’t want to receive messages from this person, consider blocking them.

### Podporuje Delta Chat obrázky, videa a jiné přílohy?

- Ano. Kromě běžného textu jsou všechny e-mailové přílohy zobrazeny jako samostatné zprávy. V odchozích zprávách jsou přílohy použity samočinně.

- For performance, images are optimized and sent at a smaller size by default, but you can send it as a “file” to preserve the original.

### How can I add or switch between multiple accounts?

You can easily work with additional accounts on Delta Chat mobile and desktop clients by clicking either:

- on the menu button and then ‘Switch Account’ (Android and desktop)
- or the profile icon and then ‘Add Account’ (iOS)

You may also wish to learn how to add accounts to multiple devices.

### Kdo uvidí můj profilový obrázek?

- Profilový obrázek lze zvolit v nastavení. Když napíšeš svému kontaktu, nebo přidáš nový vyfocením QR kódu, tyto kontakty automaticky uvidí tvůj profilový obrázek.

- Contacts who don’t use Delta Chat do not see the profile picture (however, of course, they can install Delta Chat :)

- Z důvodu soukromí nikdo nevidí tvůj profilový obrázek dokud jim nenapíšeš.

Profilový obrázek není posílán s každou zprávou, ale dostatečně často k tomu aby tvé kontakty zvuobdrželi obrázek i když začnou používat nové zařízení.

### Umí Delta Chat pracovat s e-maily v HTML?

Yes, incoming HTML messages come with a “Show full message” button. Outgoing messages always use plain text.

### Proč musím Delta Chatu zadat mé e-mailové heslo? Je to bezpečné?

Podobně jako ostatní e-mailové programy, např. Thunderbird nebo Outlook, program potřebuje heslo k tomu aby mohl posílat e-maily. Samozřejmě, že heslo je uloženo pouze na tvém přístroji. Heslo je přenášeno pouze při přihlašení k e-mailovému serveru, který má i beztak přístup k tvým e-mailům.

Poskytovatelé e-mailu s podporou OAuth2, např. “gmail.com” či “yandex.ru”, nepotřebují při přihlašování tvé heslo. V takovém případě je uložen pouze vygenerovaný přístupový kód.

Delta Chat má otevřený zdrojový kód, ze kterého lze ověřit, že program s osobními daty zachází bezpečně. Jsme rádi za každou odezvu, která udělá Delta Chat bezpečnější pro všechny.

### Jaká oprávnění Delta Chat potřebuje?

Dle užívaného operačního systému můžeš být dotázán na udělení povolení této aplikaci. Zde je co Delta Chat dělá s těmito povoleními:

- Kamera (může být zakázána)
  - fotit a filmovat: zasílat Fotky
- Kontakty (mohou být zakázané)
  - číst tvé kontakty: objevovat kontakty pro hovory
- Poloha (může být zakázaná)
  - přístup k přibližné poloze (poloha z GSM sítě): pro funkci “vysílání” polohy
  - přístup k přesné poloze (poloha z GPS a sítě GSM): pro funkci “vysílání” polohy
- Mikrofon (může být zakázaný)
  - nahrávat zvuk: pro hlasové zprávy
- Úložiště (může být zakázané)
  - upravovat a mazat obsah tvé SD karty: stahování příloh zpráv
  - číst obsah tvé SD karty: sdílet soubory s tvými kontakty
- Další schopnosti aplikace
  - měnit nastavení zvuku: lze měnit zvuky vyzvánění a hlasitost oznámení a zvukových zpráv
  - spouštět se při startu: nemusíš spouštět Delta Chat ručně
  - ovládat chvění: pro oznámení
  - značit síťová připojení: pro připojení k tvému poskytovateli e-mailu.
  - zamezit režimu spánku: pro snadnější přepis čísel bezpečnostního kódu při přenosu Nastavení Autokryptu
  - plný přístup k síti: pro připojení k poskytovateli e-mailu
  - vidět Wi-Fi připojenís: pro připojení k poskytovateli e-mailu
  - zamezit přizpůsobení se baterii: pro uživatele, kteří chtějí přijímat zprávy bez přerušení

### What means Pinning, Muting, Archiving?

Use these tools to organize your chats and keep everything in its place:

- Pinned chats always stay atop of the chat list. You can use them to access your most loved chats quickly or temporarily to not forget about things.

- Mute chats if you do not want to get notifications for them. Muted chats stay in place and you can also pin a muted chat.

- Archive chats if you do not want to see them in your chat list any longer. Archived chats remain accessible above the chat list or via search.

- When an archived chat gets a new message, unless muted, it will pop out of the archive and back into your chat list. Muted chats stay archived until you unarchive them manually.

To archive or pin a chat, long tap (Android), use the chat’s menu (Android/Desktop) or swipe to the left (iOS); to mute a chat, use the chat’s menu (Android/Desktop) or the chat’s profile (iOS).

### What does the green dot mean?

- Since Delta Chat 1.34 you can sometimes see a “green dot” next to the avatar of a contact. It means they were “recently seen”.
- In detail: it means, that in the last 10 minutes, Delta Chat has seen them:
  - either because they messaged you directly,
  - because they wrote something to a group you are both a member of,
  - because they sent you a read receipt for a message you wrote,
  - or because they sent data to your Delta Chat app by using a webxdc app.
- So this is not a real time online status - and if someone doesn’t answer right away even though they seem to be online, don’t worry and give them some space ;-)
- On the other hand, others will not always “see that you are online”. If you have turned off read receipts, they will not see the green dot until you message them or write to a group they’re in as well.

### How do disappearing messages work?

You can turn on “disappearing messages” in the settings of a chat, at the top right of the chat window, by selecting a time span between 30 seconds and 5 weeks.

Until the setting is turned off again, each chat member’s Delta Chat app takes care of deleting the messages after the selected time span. The time span begins when the receiver first sees the message in Delta Chat. The messages are deleted both in each email account on the server, and in the app itself.

Note that you can rely on disappearing messages only as long as you trust your chat partners; malicious chat partners can take photos, or otherwise save, copy or forward messages before deletion.

Apart from that, if one chat partner uninstalls Delta Chat, the messages will not get deleted from their email account. They will most likely also not be decryptable anymore (as long as they were encrypted in the first place).

### How can I delete my account?

As you use an e-mail account for Delta Chat, how you can delete your account depends on your e-mail provider. We don’t have any control over your e-mail account, so unfortunately we can’t help you with that.

If you want to keep the account, but uninstall Delta Chat, it is recommended to leave any group chat before uninstalling Delta Chat.

## Skupiny

### Vytvoření skupiny

- Z menu v pravém horním rohu, nebo stiskem příslušného tlačítka na Androidu / iOS vyber Nový hovor a pak Nová skupina.
- Na další obrazovce, vyber členy skupiny a zadej Název skupiny. Také můžeš vybrat obrázek skupiny.
- Jakmile do skupiny pošleš první zprávu, všichni členové budou vyrozuměni o nové skupině a mohou do ní také psát (dokud nepošleš první zprávu členové skupiny o ní nebudou vědět).

### Přidat členy skupiny

- Každý člen skupiny má “stejná práva” jako ostatní. Kdokoli může vymazat jakéhokoli člena, a přidat nového člena.
- K přidání a mazání členů, klikněte v hovoru na název skupiny..

### Kdyź se nedopatřením odstraníš.

- Když nejsi členem skupiny nelze se znovu připojit. Nicméně, není to velká potíž - požádej běžnou zprávou jiného člena skupiny o znovupřipojení.

### Nechci již přijímat zprávy ze skupiny.

- Buď se odeber ze seznamu členů a nebo vymaž celý skupinový hovor. K opětovnému připojení v budoucnu požádej nějakého člena skupiny o znovupřidání.

- Jiná možnost je “Umlčení” skupiny, což znamená nadále přijímat a také posílat zprávy, ale nebudeš dostávat upozrnění na nově příchozí zprávy.

### What do the ticks shown beside outgoing messages mean?

- One tick means that the message was sent successfully to your provider.
- Two ticks mean that at least one recipient’s device reported back to having received the message.
- Recipients may have disabled read-receipts, so even if you see only one tick, the message may have been read.
- The other way round, two ticks do not automatically mean that a human has read or understood the message ;)

### What happens if I turn on “Delete old messages from server”?

- By default, Delta Chat stores all messages locally on your device. If you e.g. want to save storage space at your mail provider, you can configure Delta Chat to delete old already-received messages on the server automatically. They still remain on your device until you delete them there, too.

- To turn it on, go to Delete Old Messages → Delete Messages from Server in the “Chats and Media” settings. You can set a timeframe between “At once” and “After 1 year”. All e-mails received by Delta Chat will be deleted from the server after this timeframe.

- Note that if you use Delta Chat on more than one device, you need to leave the message on the server with a sufficient timeframe so that the other device(s) can download them, too.

### What happens if I turn on “Delete old messages from device”?

- If you want to save storage on your device, you can choose to delete old messages automatically.
- To turn it on, go to “delete old messages from device” in the “Chats & Media” settings. You can set a timeframe between “after an hour” and “after a year”; this way, all messages will be deleted from your device as soon as they are older than that.

## Encryption and Security

### Which standards are used for end-to-end encryption?

Autocrypt is used for automatically establishing end-to-end encryption with contacts and group chats. Autocrypt uses a limited and secure subset of the OpenPGP standard. End-to-End encrypted messages are marked with a padlock .

Secure-Join protocols are used for establishing chats with guaranteed end-to-end encryption which protects against network attacks and compromised servers. Chats marked with a green checkmark guarantee end-to-end encrypted messages.

### How can i know if messages are end-to-end encrypted?

All end-to-end encrypted messages carry a padlock:

End-to-end encryption is guaranteed if there is a green checkmark next to the chat title:

### How can I get guaranteed end-to-end encryption and green checkmarks?

Meet your chat partner outside Delta Chat, preferably in person but a second channel like a video chat or a different messenger is fine as well. Perform the following QR show/scan procedure with your chat partner. One of you is the “Inviter”, the other is the “Joiner”.

Inviter side:

- Group invitation: Tap the chat group title to see its member list, and select “QR Invite code”. Share the QR image with the other side either in person or through a second channel.

- Direct 1:1 chat invitation: Tap the QR Code icon on the Delta Chat app main screen – on Desktop the QR Icon is in the left-side sandwich menu. Share the QR image with the other side either in person or through a second channel.

Joiner side:

- Tap the QR Code icon on the Delta Chat app main screen – on Desktop the QR Icon is in the left-side sandwich menu.

- Choose “SCAN QR CODE” and scan the QR Code that you see from your chat partner in a second channel.

- Tap “OK”

Both Inviter and Joiner:

Wait while Secure-Join network messages are exchanged between both devices.

- If both devices are online, both sides will eventually see a (group or direct) chat with a green checkmark next to the title.

- If one of the devices is offline, the green checkmarks will only appear later when the device is internet-connected again and the Secure-Join network protocol completed.

Congratulations! You now will automatically use guaranteed end-to-end encryption with this contact and both of you can add each other to green-checkmarked groups , thereby automatically spreading guaranteed end-to-end encryption among its members.

### What does the green checkmark and “guaranteed end-to-end encryption” mean?

Chat titles with green checkmarks mean that all messages in the chat will be end-to-end encrypted and can not be read or altered by compromised e-mail servers or Internet providers. Joining green-checkmarked group chats safely spreads everybody’s encryption information (and green checkmarks) in a manner that guarantees end-to-end encryption in the group and among members.

Contact profiles with green checkmarks mean that messaging a contact is currently guaranteed to be end-to-end encrypted. Every green-checkmarked contact either did a direct QR-scan with you or was introduced by a another green-checkmarked contact. Introductions happen automatically when adding members to groups. Whoever adds a contact to a green-checkmarked group becomes an introducer to those members who didn’t yet know about the added contact. In a contact profile you can tap on the “Introduced by …” text repeatedly until you get to the one with whom you directly did a QR-scan.

Note that in a contact profile you may see and tap introducers but there is no green checkmark in the profile title. This usually means that the contact “sent a message from another device”.

For more in-depth discussion of “guaranteed end-to-end encryption” please see Secure-Join protocols and specifically read about “Verified Groups”, the technical term of what is called here “green-checkmarked” or “guaranteed end-to-end encrypted” chats.

### A contact “sent a message from another device”, what can i do?

Your chat with a contact lost guaranteed end-to-end encryption. The green checkmark was removed for this chat and contact when you see this warning. If you find the sudden drop of guaranteed end-to-end encryption surprising for this contact then don’t accept the warning! Instead check with your contact through a second channel like a video call, other messenger or a phone call, to find out what happened.

If your contact actually caused the drop of guaranteed end-to-end encryption please see the next paragraphs for common reasons and their mitigations. Regardless, all other green-checkmarked chats remain guaranteed end-to-end encrypted even if the contact is a member there.

Your contact is using Delta Chat on a second device (phone or laptop)

If they have another device with a Delta Chat app running, they should remove the account from the new device and add it as a second device as described here. As soon as they message you afterwards, the warning will be gone and guaranteed encryption is established with both devices of your contact.

Your contact reinstalled Delta Chat using their old account login

If they have a backup file, they should remove the account from the new device and rather import the backup file to re-create their account. As soon as they message you afterwards, the warning will be gone and guaranteed encryption is re-established for this contact.

If they don’t have a backup file, it’s best to perform a QR scan with your chat partner to re-establish guaranteed end-to-end encryption.

Your contact sent a mail through a webmail interface or another e-mail app and will get back to using Delta Chat soon again.

If you are sure that the contact sometimes uses webmail, or another mail app lacking end-to-end encryption, then you may accept the warning. As soon as your contact uses Delta Chat again, guaranteed end-to-end encryption will be automatically re-established.

Your contact stopped using Delta Chat entirely

Sometimes remaining in contact is more important than end-to-end encryption. “Transport Layer Encryption” (TLS) may still meaningfully protect the confidentiality of your messages between your device and the e-mail server. But without end-to-end encryption you and your contact are trusting your e-mail server to not read or manipulate your messages, and to not hand them to third parties.

In any case, you can not do much else than accept the warning. Please also remove the contact from any active green-checkmarked group which you can find in “Shared chats” in the Contact profile. This spares your contact from getting “unreadable” messages.

If the contact removed Delta Chat because of buggy or undesirable behaviour, please consider posting to our support forum to help us identify and address common problems. Thanks!

### Are attachments (pictures, files, audio etc.) end-to-end encrypted?

Yes.

When we talk about an “end-to-end encrypted message” we always mean a whole message is encrypted, including all the attachments and attachment metadata such as filenames.

### Is OpenPGP secure?

Yes, Delta Chat uses a secure subset of OpenPGP and only displays a padlock security indicator on a message if the whole message is properly encrypted and signed. For example, “Detached signatures” are not treated as secure.

OpenPGP is not insecure by itself. Most publically discussed OpenPGP security problems actually stem from bad usability or bad implementations of tools or apps (or both). It is particularly important to distinguish between OpenPGP, the IETF encryption standard, and GnuPG (GPG), a command line tool implementing OpenPGP. Many public critiques of OpenPGP actually discuss GnuPG which Delta Chat has never used. Delta Chat rather uses the OpenPGP Rust implementation rPGP, available as an independent “pgp” package, and security-audited in 2019.

We aim, along with other OpenPGP implementors, to further improve security characteristics by implementing the new IETF OpenPGP Crypto-Refresh which was thankfully adopted in summer 2023.

### Did you consider using alternatives to OpenPGP for end-to-end -encryption?

Yes, we are following efforts like MLS or Saltpack but adopting them would mean breaking end-to-end encryption interoperability with all other e-mail apps that typically support OpenPGP encryption. So it would not be a light decision to take and there must be tangible improvements for users.

Delta Chat takes a holistic “usable security” approach and works with a wide range of activist groupings as well as renowned researchers such as TeamUSEC to improve actual user outcomes against security threats. The wire protocol and standard for establishing end-to-end encryption is only one part of “user outcomes”, see also our answers to device-seizure and message-metadata questions.

### Is Delta Chat vulnerable to EFAIL?

No, Delta Chat never was vulnerable to EFAIL because its OpenPGP implementation rPGP uses Modification Detection Code when encrypting messages and returns an error if the Modification Detection Code is incorrect.

Delta Chat also never was vulnerable to the “Direct Exfiltration” EFAIL attack because it only decrypts `multipart/encrypted` messages which contain exactly one encrypted and signed part, as defined by the Autocrypt Level 1 specification.

### Is a message exposed in cleartext if end-to-end encryption is not available?

Even if your messages are not guaranteed to be end-to-end encrypted, they are still protected from Internet providers like cell or cable companies. However, your and your recipient’s e-mail providers may read, analyze or even modify your messages, including any attachments, if they are not end-to-end encrypted.

Delta Chat by default uses strict TLS encryption which secures connections between your device and your e-mail provider. All of Delta Chat’s TLS-handling has been independently security audited. Moreover, the connection between your and the recipient’s e-mail provider will typically be transport-encrypted as well. If the involved e-mail servers support MTA-STS then transport encryption will be enforced between e-mail providers in which case Delta Chat communications will never be exposed in cleartext to the Internet even if the message was not end-to-end encrypted.

Note that maintaining guaranteed end-to-end encryption on top of TLS encryption provides pervasive safety between your and the recipient’s devices. Not even your e-mail or Internet provider will be able to read or modify your messages.

### How does Delta Chat protect metadata in messages?

Delta Chat protects most message metadata by putting the following information into the end-to-end encrypted part of messages:

- Subject line
- Group avatar and name
- MDN (read receipt) requests (`Chat-Disposition-Notification-To`)
- Disappearing message timer (`Ephemeral-Timer`)
- `Chat-Group-Member-Removed`, `Chat-Group-Member-Added`
- `Secure-Join` header containing secure join commands
- Notification about enabling location streaming
- WebRTC room URL

E-Mail servers do not get access to this protected metadata but they do see the message date as well as the message size, and, more importantly, the sender and receiver addresses. E-mail servers need receiver addresses to route and deliver messages to recipient’s devices.

### How to protect metadata and contacts when a device is seized?

Both for protecting against metadata-collecting e-mail servers as well as against the threat of device seizure we recommend to use a Delta Chat optimized e-mail server instance to create pseudonymous temporary accounts through QR-code scans. Note that Delta Chat apps on all platforms support multiple accounts so you can easily use action-specific “1-week” or “1-month” accounts next to your “main” account with the knowledge that all temporary account data, along with all metadata, will be deleted. Moreover, if a device is seized then contacts using temporary e-mail accounts can not be identified easily, as compared to messengers which reveal phone numbers in chat groups which in turn are often associated with legal identities.

### How can i check encryption information?

You may check the end-to-end encryption status manually in the “Encryption” dialog (user profile on Android/iOS or right-click a user’s chat-list item on desktop). Delta Chat shows two fingerprints there. If the same fingerprints appear on your own and your contact’s device, the connection is safe.

### How can I check the encryption status of messages?

A little padlock in a message bubble denotes that the message was properly end-to-end encrypted from the given sender. If there is no padlock, the message was not properly end-to-end encrypted most likely because the sender uses an app or webmail interface without support for end-to-end–encryption.

### Why do I see unencrypted messages?

If a contact uses a non-Autocrypt e-mail app, all messages involving this contact (in a group or 1:1 chat) will not be end-to-end encrypted, and thus not show a “padlock” with messages. Note that even if your contacts use Delta Chat on their account, they might also use a non-Autocrypt e-mail app on that account which then may cause intermittently unencrypted messages. Replying unencrypted to unencrypted messages is mandated by Autocrypt to prevent unreadable messages on the side of your contacts and their non-Autocrypt e-mail app.

### How can i get an end-to-end encrypted chat with a Delta Chat contact who sometimes uses webmail or another non-Autocrypt e-mail app?

If you need a safely end-to-end encrypted chat with a contact who is using their account both with Delta Chat and non-Autocrypt apps (e.g. webmail), it’s best to setup guaranteed end-to-end encryption with them and then create a guaranteed end-to-end encrypted group chat with you two as members. In this group chat all messages will be end-to-end encrypted even if the direct chat between you two has a “… sent a message from another device” warning.

### How can I ensure message end-to-end encryption and deletion?

The best way to ensure every message is end-to-end encrypted, and metadata deleted as quickly as possible is using chats with guaranteed end-to-end encryption and turning on disappearing messages.

Guaranteed end-to-end encrypted chats protect against MITM attacks and turning on disappearing messages deletes the messages on the server after a user-configured time.

If you don’t need a longer-lived copy of your messages on the server, you can also turn on “delete messages from server automatically”.

### Does Delta Chat support Perfect Forward Secrecy?

No, Delta Chat doesn’t support Perfect Forward Secrecy (PFS). This means that if your Delta Chat private decryption key is leaked, and someone has collected your prior in-transit messages, they will be able to decrypt and read them using the leaked decryption key.

Note, however, that if anyone obtains to your decryption keys, they will typically also be able to obtain your messages, irrespective if Perfect Forward Secrecy is in place or not. The typical real-world situation for leaked decryption keys is device seizure which we discuss in our answer on metadata and device seizure.

It is possible that Delta Chat evolves to support Perfect Forward Secrecy, because OpenPGP is just a container for encrypted messages but encryption key management (and thus key rotation or key “ratcheting”) could be organized in flexible ways. See Seqouia’s PFS prototype for existing experiments in the OpenPGP implementor community.

### Is end-to-end encryption of Delta Chat as safe as Signal?

It depends on what is important to you. Delta Chat does not support PFS like Signal does but it provides guaranteed end-to-end encrypted chats that are safe against compromised servers or corrupted networks. Signal and most other PFS-supporting messengers do not provide a practical scheme for protecting chat groups from network attacks which are arguably more worrysome than a potential attacker who seizes your phone and private encryption setup but somehow not your messages, yet has a full record of all past encrypted messages.

In any case, Delta Chat’s end-to-end encryption uses a secure subset of OpenPGP which has been independently security-audited.

### Lze znovu použít můj stávající soukromý klíč?

Yes. The best way is to send an Autocrypt Setup Message from the other e-mail client. Look for something like Start Autocrypt Setup Transfer in the settings of the other client and follow the instructions shown there.

Alternatively, you can import the key manually in “Settings -> Advanced settings -> Import secret keys”. Caution: Make sure the key is not protected by a password, or remove the password beforehand.

If you don’t have a key or don’t even know you would need one - don’t worry: Delta Chat generates keys as needed, you don’t have to hit a button for it.

### Nemohu do Delta Chatu zavést můj stávající PGP klíč.

Nejpravděpodobnější příčinou jsou zašifrované klíče, nebo klíče s heslem. Takové klíče Delta Chat nepodporuje. Můžeš odstranit šifrování nebo heslo a zkusit to znovu. Pokud je potřeba použít zaheslovaný klíč vytvoř / použij zástupnou adresua a pak přidej nový Delta Chat účet s tímto klíčem.

Delta Chat podporuje běžné formáty OpenPGP klíčů, nicméně neočekáváme, že soukromé klíče ze všech aplikací budou fungovat. To není cíl, a ve skutečnosti věttšina nových uživatelů Delta Chatu nemá žádný stávající klíč. Přesto se snažíme podporovat soukromé klíče z co nejvíce možných zdrojů.

Odstranění hesla ze soukromého klíče závisí na programu ze kterého PGP klíč pochází. Enigmail umí nastavit prázdnou hodnotu hesla v okně Key Management. U GnuPG lze to samé nastavit z příkazové řádky. Pro ostatní programy by mělo jít nalézt řešení na Interentu.

## Více klientů najednou

### Lze Delta Chat používat souběžně na více zařízeních?

Yes. Delta Chat 1.36 comes with a new, experimental function for using the same account on different devices:

- Make sure both devices are on the same Wi-Fi or network

- On the first device, go to Settings → Add Second Device, unlock the screen if needed and wait a moment until a QR code is shown

- On the second device, install Delta Chat

- On the second device, start Delta Chat, select Add as Second Device, and scan the QR code from the old device

- Transfer should start after a few seconds and during transfer both devices will show the progress. Wait until it is finished on both devices.

In contrast to many other messengers, after successful transfer, both devices are completely independent. One device is not needed for the other to work.

### Troubleshooting

- Double-check both devices are in the same Wi-Fi or network

- Your system might have a “personal firewall”, which is known to cause problems (especially on Windows). Disable the personal firewall for Delta Chat on both ends and try again

- Ensure there is enough storage on the destination device

- If transfer started, make sure, the devices stay active and do not fall asleep. Do not exit Delta Chat. (we try hard to make the app work in background, but systems tend to kill apps, unfortunately)

- Delta Chat is already logged in on the destination device? You can use multiple accounts per device, just add another account

- If you still have problems or if you cannot scan a QR code try the manual transfer described below

### Manual Transfer

This method is only recommended if “Add Second Device” as described above does not work.

- On the old device, go to “Settings -> Chats and media -> Export Backup”. Enter your screen unlock PIN, pattern, or password. Then you can click on “Start Backup”. This saves the backup file to your device. Now you have to transfer it to the other device somehow.
- On the new device, on the login screen, instead of logging into your email account, choose “Import Backup”. After import, your conversations, encryption keys, and media should be copied to the new device.
  - If you use iOS: and you encounter difficulties, maybe this guide will help you.
- You are now synchronized, and can use both devices for sending and receiving end-to-end encrypted messages with your communication partners.

### Je v plánu vytvořit webovou verzi Delta Chatu?

- Zatím ne, pouze nějaké úvodní myšlenky ohledně takového vývoje.
- Jsou 2-3 cesty jak uvést Delta Chatu na Web, ale všechny představují významné úsilí. V tuto chvíli jsme zaměřeni na poskytování stabilní verze jako nativní aplikace ve všech významných obchodech (Google Play / iOS / Windows / macOS / Linux repositories) .
- Pokud nemáš dostatečná práva instalovat programy na svůj pracovní počítač, můžeš použít přenosnou verzi pro Windows nebo AppImage pro Linux. Všechny softwarové balíčky jsou na get.delta.chat.

### K čemu je dobré nastavení “Posílat si kopii”?

Posílat si kopii zpráv zaručuje, že zprávy se zobrazí na všech současně nastavených zařízeních. Pokud máš několik zařízení a nezapneš tuto funkci, uvidíš pouze příchozí zprávy, a zprávy odeslané jen z právě používaného přístroje. Ty odeslané z ostatních zařízení neuvidíš.

Kopie přijdou nejdříve do Příchozí složky, a pak jsou samočinně přesunuty do složky DeltaChat; ne do složky Odeslané. Do složky Odeslané se nepřesouvá nikdy nic. protože by to vyžadovalo přenášet zprávu dvakrát (jednou poslat přes SMTP, a jednou pro složku Odeslané přes IMAP).

Výchozí hodnota nastavení pro zasílání si kopií je “Ne”.

### Proč můžu nastavit sledování složky Odeslané?

Jediný důvod sledovat složku s odeslanými zprávami je používání jiného e-mailového programu (např. Thunderbird) spolu s Delta Chatem, a chtít z tohoto programu také psát zprávy do hovorů Delta Chatu.

Nicméně doporučujeme používat Delta Chat Desktop Client; ten lze stáhnout z get.delta.chat. Možnost sledování složky “Odeslané” může být v budoucnu zrušena. Byla totiž vytvořena v době, kdy Delta Chat Desktop nebyl dostupný na všech platformách.

### Proč mohu zvolit nesledovat složku DeltaChat?

Někteří lidé užívají Delta Chat jako jediný e-mailový program, a chtějí užívat složku Příchozí / Inbox pro všechny zprávy i místo složky DeltaChat. Pokud zrušíš “Sleduj složku DeltaChat”, zruš také “přesouvat zprávy do složky DeltaChat”. Jinak hrozí, že mazání zpráv či nastavení na několika zařízeních nebude správně fungovat.

## webxdc apps

In Delta Chat, you can share webxdc apps, attachments with an `.xdc` file extension. They can do very different things, and make Delta Chat a truly extendable messenger.

### How private are webxdc apps?

- webxdc apps can not send data to the Internet, or download anything.
- A webxdc app can only exchange data within a Delta Chat chat, with its copies on the devices of your chat partners. Other than that, it’s completely isolated from the Internet.
- The privacy a webxdc app offers is the privacy of your chat - as long as you trust the people you chat with, you can trust the webxdc app as well.
- This also means: it can be a privacy risk to open webxdc apps in chats where you don’t trust the members - as you know it from e-mail attachments, where you only open attachments from senders you trust, and not from spammers.

### Where can I get webxdc apps?

- In general, anyone can share webxdc apps with each other without restrictions.
- You can send ‘hi’ to xstore@testrun.org to see an experimental webxdc appstore. All of the apps are open source and for free.
- Many people write their own webxdc apps and post them to the Delta Chat forum.

### How can I create my own webxdc apps?

- webxdc apps are just zip files containing html, css, and javascript code.
- You can extend the Hello World example app to get started.
- All else you need to know is written in the documentation.
- If you have question, you can ask others with experience in the Delta Chat Forum.

## Experimental Features

We are very grateful for feedback on these features - do you want to share your ideas? Join the Forum to contribute. You may conveniently login via Delta Chat and a QR code scan, another rather stable experiment we run on the side (sic!).

### How can I use audio/video calls with Delta Chat?

- To turn on audio/video calls, go to the “experimental features” section in the advanced settings and choose a “Video Chat Instance”.
- When you invite others to a video chat, it is opened in your browser/app at once. The others receive an e-mail with a link to the video chat. This way, it is also compatible if your chat partners don’t use Delta Chat.
- Note that there is no ring tone on the other side, and your chat partners will not get interrupted by a video chat invite.
- You can use any video chat service which allows joining by link. Just add the link in the settings.
- For example, to use the flagship Jitsi Meet instance, you could enter `https://meet.jit.si/$ROOM`. The `$ROOM` variable will be a random value; this way, you will have a new random jitsi room every time you call someone.

### What are Broadcast Lists and how can I use them?

- With a Broadcast List you can send a message to many recipents at once; when they reply to you, you get the reply in your direct 1:1 chat with them. The recipients can’t see each other.
- Technically, it is an E-Mail with many recipients in BCC.
- You can turn on the feature in the “experimental features” section in the advanced settings. Then you can create a Broadcast List from the “New Chat” dialog.
- In case you are using more than one device, Broadcast Lists are currently not synced between them.
- Messages sent to broadcast lists are not encrypted. Encryption would break anonymity, because then all recipients would know who else received it (Sending individual mails to everyone would be worse for rate limit and network consumption reason).

### How can I share my location with my chat partners?

- You can turn on location streaming in the “experimental features” section of the advanced settings.
- Now, if you want to share your location in a chat, go to “attach” and select “location”. You can now set a time frame in which your location will be streamed to your chat partners, between 5 minutes and 6 hours.
- When your location changes, the others in the chat can view it on a map in the chat.
- To see the map and view locations of others, you need to turn on the feature in the advanced settings.
- This feature will not share your location with anyone except your chat partners. But: to show the map, we need to download map tiles from mapbox.com, so if you view the map, mapbox.com is asked for the map of a specific area. If this is a privacy risk for you, this feature might not be for you. We are working on finding a decentralized alternative for Mapbox.
- On desktop, the OS typically can’t determine your location. Instead you can right click on the map and describe a location, which is sent to the chat as a message, but also appears on the map.

### What does the experimental database encryption actually protect?

- Right now, the database encryption is still very experimental. Don’t rely on it for protection, you should additionally use encryption of your operating system, if it provides any.
- The database encryption does not yet encrypt the blobs, only the rows and columns of the database. This more or less means that your messages are safe, but not your attachments.
- For iOS and Android, the encryption keys are stored in the system keychain. This means the encryption is as secure as the operating system it’s running on.
- The Delta Chat desktop client doesn’t offer database encryption yet, as there is no standard way to store the encryption keys on the different supported platforms.

### Why can I choose to only watch the DeltaChat folder?

Toto je pokusné nastavení pro některé uživatele, kteří používají vlastní pravidla pro třídění e-mailu na serveru. Ne všichni poskytovatelé toto nabízí, ale někteří umožňují samočinně přesouvat všechny e-maily s hlavičkou “Chat-Version” do složky DeltaChat. To je něco co za běžných okolností dělá Delta Chat sám.

Enabling “Only Fetch from DeltaChat folder” makes sense if you have both:

- zapnuté pravidlo na serveru, které přesouvá zprávy s hlavičkou Chat-Version do složky DeltaChat, a
- nastaveno “Zobrazuj běžné e-maily” na “Ne, pouze hovory”.

In this case, Delta Chat doesn’t need to watch the Inbox, and it’s enough to only watch the DeltaChat folder.

### How can I change my account to a different e-mail address?

1. Change your address in “Settings - Password and Account” and enter the password of your new account (and if necessary, server settings). You will get an information notice about the fact that you are moving to a new address. An additional notice will also show up in your “Device messages” chat.

2. If possible, let your old e-mail provider forward all messages to your new address.

3. Tell your contacts that you changed your address. Writing to guaranteed end-to-end encrypted chats and groups, will make them notice your move automatically and they will continue chatting with you using your new address.

Note that Delta Chat will not retrieve messages anymore from your old e-mail provider. If you didn’t configure your e-mail provider to forward messages (step 2.) only those contacts to whom you sent a message in a guaranteed end-to-end encrypted chat will send messages to your new address.

To learn more about this the details behind this, read our blogpost on it.

## Různé

### Pracuje Delta Chat s mým poskytovatelem e-mailu?

- S poměrně vysokou pravděpodobností: Ano :)
  Nicméně, někteří poskytovatelé vyžadují ke správnému chodu speciální nastavení, podrobnější popis je na Provider Overview

### I want to manage my own e-mail server for Delta Chat. What do you recommend?

- Most mail servers will work well. But what we personally recommend is a combination of mailcow and mailadm, as described in this blogpost.
- You can find an installation guide on our website.

### Je hovor v Delta Chatu skutečně interaktivní, když užívá E-Mail?

- Sending and receiving messages takes a few seconds, typically. Sometimes there are cases where it takes longer but that is arguably true as well for any other messenger.
- Instant chatting works fast if both parties are actively using the app. It’s sometimes slower if the app is running in the background.
- Receiving messages then can take minutes because both Android and iOS often stop Delta Chat from running in the background, and only wake it up occasionally. This artificial delay is usually worse on iOS than on Android.
- However, Android and iOS kill apps running in the background is a problem for many legitimate apps. For more information, see dontkillmyapp.com.

### Lze Delta Chat používat s Protonmail / Tutanota / Criptext?

- Yes and No.
- No, you can not use your Protonmail, Tutanota, or Criptext account with Delta Chat; they do not offer receiving mails via IMAP.
- In any case you can use Delta Chat to send Messages to people who use Protonmail, Tutanota, or Criptext. Those messages will not be end-to-end encrypted, though. The end-to-end encryption those providers offer is not compatible with Autocrypt, the standard Delta Chat uses.
- Delta Chat can end-to-end-encrypt through any e-mail provider with any Autocrypt-enabled e-mail app.

### Mám zájem o technické podrobnosti. Kde najdu víc?

- Dobrý začátek je Standards used in Delta Chat.

### Was Delta Chat independently audited for security vulnerabilities?

The Delta Chat project underwent four independent security audits in the last years:

- In 2019, Include Security analyzed Delta Chat’s PGP and RSA libraries. It found no critical issues, but two high-severity issues that we subsequently fixed. It also revealed one medium-severity and some less severe issues, but there was no way to exploit these vulnerabilities in the Delta Chat implementation. Some of them we nevertheless fixed since the audit was concluded. You can read the full report here.

- In 2020, Include Security analyzed Delta Chat’s Rust core, IMAP, SMTP, and TLS libraries. It did not find any critical or high-severity issues. The report raised a few medium-severity weaknesses - they are no threat to Delta Chat users on their own because they depend on the environment in which Delta Chat is used. For usability and compatibility reasons, we can not mitigate all of them and decided to provide security recommendations to threatened users. You can read the full report here.

- Beginning 2023, Cure53 analyzed both the transport encryption of Delta Chat’s network connections and a reproducible mail server setup as recommended on this site. You can read more about the audit on our blog or read the full report here.

- Beginning 2023, we fixed security and privacy issues with the “web apps shared in a chat” feature, related to failures of sandboxing especially with Chromium. We subsequently got an independent security audit from Cure53 and all issues found were fixed in the 1.36 app series released in April 2023. See here for the full background story on end-to-end security in the web.

### Jak je financován vývoj Delta Chatu?

Delta Chat does not receive any Venture Capital and is not indebted, and under no pressure to produce huge profits, or to sell users and their friends and family to advertisers (or worse). We rather use public funding sources, so far from EU and US origins, to help our efforts in instigating a decentralized and diverse chat messaging eco-system based on Free and Open-Source community developments.

Concretely, Delta Chat developments have so far been funded from these sources:

- The NEXTLEAP EU project funded the research and implementation of verified groups and setup contact protocols in 2017 and 2018 and also helped to integrate end-to-end Encryption through Autocrypt.

- The Open Technology Fund gave us a first 2018/2019 grant (~$200K) during which we majorly improved the Android app and released a first Desktop app beta version, and which moreover moored our feature developments in UX research in human rights contexts, see our concluding Needfinding and UX report. The second 2019/2020 grant (~$300K) helped us to release Delta/iOS versions, to convert our core library to Rust, and to provide new features for all platforms.

- The NLnet foundation granted in 2019/2020 EUR 46K for completing Rust/Python bindings and instigating a Chat-bot eco-system.

- In 2021 we received further EU funding for two Next-Generation-Internet proposals, namely for EPPD - e-mail provider portability directory (~97K EUR) and AEAP - email address porting (~90K EUR) which resulted in better multi-account support, improved QR-code contact and group setups and many networking improvements on all platforms.

- From End 2021 till March 2023 we received Internet Freedom funding (500K USD) from the U.S. Bureau of Democracy, Human Rights and Labor (DRL). This funding supported our long-running goals to make Delta Chat more usable and compatible with a wide range of e-mail servers world-wide, and more resilient and secure in places often affected by internet censorship and shutdowns.

- Beginning 2023 we got accepted in the Next Generation Internet (NGI) Entrust program for our “Private Decentralized Apps” proposals. Exact amount is to be determined (around 100K EUR). This funding supports further developments of webxdc “apps shared in a chat”.

- Sometimes we receive one-time donations from private individuals. For example, in 2021 a generous individual bank-wired us 4K EUR with the subject “keep up the good developments!”. 💜 We use such money to fund development gatherings or to care for ad-hoc expenses that can not easily be predicted for, or reimbursed from, public funding grants. Receiving more donations also helps us to become more independent and long-term viable as a contributor community.

- Velice významnou pomocí je práce expertů a nadšenců prováděná bez nároku na honorář či za minimální odměnu ve prospěch veřejného dobra. Je třeba zdůraznit, že bez nich by se Delta Chat nepřibližoval ani zdaleka současnému stavu.

The monetary funding mentioned above is mostly organized by merlinux GmbH in Freiburg (Germany), and is distributed to more than a dozen contributors world-wide.

Please see Delta Chat Contribution channels for both monetary and and other contribution possibilities.