all-in-one privacy solution":["Proton Unlimited es una solución de privacidad todo en uno"],"Black Friday":["Black Friday"],"No ads. Privacy by default.":["Sin anuncios. Privacidad por defecto."],"People before profits":["Primero las personas, luego los beneficios"],"Security through transparency":["Seguridad con transparencia"],"The best Proton Mail ${ BLACK_FRIDAY } deals":["Las mejores ofertas de Proton Mail en el ${ BLACK_FRIDAY }"],"The world’s only community- supported email service":["El único servicio de correo electrónico del mundo respaldado por la comunidad"]},"specialoffer:limited":{"${ hours } hour":["${ hours } hora","${ hours } horas"],"${ hoursLeft }, ${ minutesLeft } and ${ secondsLeft } left":["Tiempo restante: ${ hoursLeft }, ${ minutesLeft } y ${ secondsLeft }"],"${ minutes } minute":["${ minutes } minuto","${ minutes } minutos"],"${ seconds } second":["${ seconds } segundo","${ seconds } segundos"],"Limited time offer":["Oferta por tiempo limitado"]},"specialoffer:listitem":{"Create multiple addresses":["Cree múltiples direcciones"],"Hide-my-email aliases":["Seudónimos de hide-my-email"],"Quickly unsubscribe from newsletters":["Cancele suscripciones a boletines rápidamente"],"Use your own domain name":["Use su propio dominio"]},"specialoffer:logos":{"As featured in":["Tal como aparece en"]},"specialoffer:metadescription":{"Get an encrypted email that protects your privacy":["Obtenga un correo electrónico cifrado que protege su privacidad"]},"specialoffer:metatitle":{"Proton Mail Black Friday Sale - Up to 40% off":["Oferta de Black Friday de Proton Mail: hasta un 40% de descuento"]},"specialoffer:newmetadescription":{"Get up to 40% off Proton Mail subscriptions this Black Friday. Find great deals on our secure end-to-end encrypted email plans.":["Aproveche las rebajas de Black Friday y obtenga suscripciones de Proton Mail con hasta un 40 % de descuento. Encontrará las mejores ofertas en planes de correo electrónico seguro cifrado de extremo a extremo."]},"specialoffer:newmetatitle":{"Proton Mail Black Friday sale | Up to 40% off secure email":["Rebajas de Black Friday en Proton Mail | Hasta un 40 % de descuento en correo electrónico seguro"]},"specialoffer:note":{"* Billed at ${ TOTAL_SUM } for the first year":["*Con un costo de ${ TOTAL_SUM } durante el primer año"],"*Billed at ${ TOTAL_SUM } for the first 2 years":["*Con un costo de ${ TOTAL_SUM } durante los primeros 2 años"],"30-day money-back guarantee":["Garantía de devolución de dinero de 30 días"],"Billed at ${ TOTAL_SUM } for the first 2 years":["Con un costo de ${ TOTAL_SUM } durante los primeros 2 años"],"Billed at ${ TOTAL_SUM } for the first year":["Con un costo de ${ TOTAL_SUM } durante el primer año"],"You save ${ SAVE_SUM }":["Ahorre ${ SAVE_SUM }"]},"specialoffer:off":{"${ DISCOUNT } off":["-${ DISCOUNT }"],"${ PERCENT_OFF } off":["-${ PERCENT_OFF }"]},"specialoffer:testimonial":{"I love my ProtonMail":["Amo mi Proton Mail"],"My favorite email service":["Mi servicio de correo electrónico favorito"],"Thanks Proton for keeping us all safe in the complicated internet universe.":["Gracias Proton por mantenernos a salvo en el complicado universo de Internet."],"You get what you pay for. In the case of big tech, if you pay nothing, you get used. I quit using Gmail and switched to @ProtonMail":["Obtiene aquello por lo que paga. En el caso de la gran tecnología, cuando uno no paga nada, se acostumbra. Dejé de usar Gmail y cambié a @ProtonMail"]},"specialoffer:time":{"Days":["Días"],"Hours":["Horas"],"Min":["min"]},"specialoffer:title":{"And much more":["Y mucho más"],"Make your inbox yours":["Personalice su bandeja de entrada"],"Safe from trackers":["A salvo de rastreadores"],"Stay organized":["Mantenga el orden"],"Black Friday email deals":["Ofertas en correo electrónico del Black Friday"],"Don’t just take our word for it":["No confíe solo en nuestra palabra"],"Our story":["Nuestra historia"],"Transfer your data from Google in one click":["Transfiera sus datos de Google con un solo clic"]},"specialoffer:tooltip":{"Access blocked content and browse privately. Includes ${ TOTAL_SERVERS }+ servers in ${ TOTAL_COUNTRIES }+ countries, connect up to 10 devices, access worldwide streaming services, malware and ad-blocker, and more.":["Acceda a contenido bloqueado y navegue de forma privada. Incluye ${ TOTAL_SERVERS } servidores en más de ${ TOTAL_COUNTRIES } países, conecta hasta 10 dispositivos, acceda a servicios de transmisión en todo el mundo, malware y bloqueador de anuncios, y más."],"Easily share your calendar with your family, friends or colleagues, and view external calendars.":["Comparta su calendario con familiares, amigos y compañeros fácilmente y consulte calendarios externos."],"Includes support for 1 custom email domain, 10 email addresses, 10 hide-my-email aliases, calendar sharing, and more.":["Incluye compatibilidad con 1 dominio de correo electrónico personalizado, 10 direcciones de correo electrónico, 10 seudónimos de hide-my-email, posibilidad de compartir calendario, etc."],"Includes support for 3 custom email domains, 15 email addresses, unlimited hide-my-email aliases, calendar sharing, and more.":["Incluye compatibilidad con 3 dominios de correo electrónico personalizado, 15 direcciones de correo electrónico, seudónimos ilimitados de hide-my-email, posibilidad de compartir calendario, etc."],"Manage up to 25 calendars, mobile apps, secured with end-to-end encryption, 1-click calendar import from Google, and more.":["Administre hasta 25 calendarios, apps móviles, protegido con cifrado de extremo a extremo, importación de calendario con 1 clic desde Google y más."]},"Status Banner":{"At the moment we are experiencing issues with the Proton VPN service":["En este momento, tenemos problemas con el servicio Proton VPN."],"Learn more":["Más información"]},"Status banner":{"Learn more":["Más información"],"Please note that at the moment we are experiencing issues with the ${ issues[0] } service.":["Tenga en cuenta que, en este momento, estamos experimentando problemas con el servicio ${ issues[0] }."],"We are experiencing issues with one or more services at the moment.":["En este momento, tenemos problemas con uno o más servicios."]},"suggestions":{"Suggestions":["Sugerencias"]},"Support":{"Sub category":["Subacategoria","Subcategorías"]},"Support article":{"${ readingTime } min":["${ readingTime } minuto","${ readingTime } minutos"],"Category":["Categoría","Categorías"],"Didn’t find what you were looking for?":["¿No encontró lo que buscaba?"],"General contact":["Contacto general"],"Get help":["Obtener ayuda"],"Legal contact":["Contacto legal"],"Media contact":["Contacto para medios"],"Partnerships contact":["Contacto para colaboradores"],"Reading":["Lectura"]},"Support categories":{"Browse Proton product support":["Explore el soporte de productos de Proton"]},"Support category":{"There is no article in this category yet.":["Todavía no hay ningún artículo en esta categoría."]},"Support troubleshooting":{"--- Select ---":["--- Seleccionar ---"],"Adding and importing contacts":["Agregar e importar contactos"],"App version":["Versión de la app"],"Automatically save contacts":["Guardar contactos automáticamente"],"Bridge connection issues with Outlook, Apple Mail or Thunderbird":["Problemas de conexión de Bridge con Outlook, Apple Mail o Thunderbird"],"Browser":["Navegador"],"Check if this helps":["Compruebe si le sirve"],"Choose a category for your question":["Elija la categoría de su pregunta"],"Connectivity errors on Android and iOS":["Errores de conexión en Android y iOS"],"Contacts":["Contactos"],"Custom domain":["Dominio personalizado"],"Desktop notifications":["Notificaciones de escritorio"],"Did this solve your issue ?":["¿Resolvió su problema?"],"Difference between Combined Addresses Mode and Split Addresses Mode":["Diferencia entre el modo de direcciones combinadas y el de direcciones divididas"],"Differences between addresses, aliases, and sub-users":["Diferencias entre direcciones, alias y subusuarios"],"Email notifications":["Notificaciones de correo electrónico"],"Email tracking protection":["Protección de rastreo de correos electrónicos"],"Encryption":["Cifrado"],"Encryption keys management":["Gestión de claves de cifrado"],"Faster assistance is just a few clicks away — please make your selections":["Obtenga ayuda más rápidamente con tan solo unos clics. Haga su selección."],"How to avoid receiving spam messages":["Cómo evitar recibir mensajes de spam"],"How to block unwanted email":["Cómo bloquear correos electrónicos no deseados"],"How to configure your email client for Bridge":["Cómo configurar su cliente de correo electrónico para Bridge"],"How to create contact groups":["Cómo crear grupos de contactos"],"How to create or edit CSV contacts":["Cómo crear o editar contactos CSV"],"How to install Proton Mail Bridge":["Cómo instalar Proton Mail Bridge"],"How to merge duplicate contacts":["Cómo fusionar contactos duplicados"],"How to send encrypted messages to external users":["Cómo enviar mensajes encriptados a usuarios externos"],"How to set up a custom domain":["Cómo configurar un dominio personalizado"],"How to unsubscribe from Apple’s TestFlight notification emails":["Cómo cancelar la suscripción a los correos electrónicos de notificación de TestFlight de Apple"],"How to use auto-reply":["Cómo utilizar la respuesta automática"],"How to use filters":["Cómo utilizar los filtros"],"How to use folders and labels":["Cómo utilizar las carpetas y las etiquetas"],"How to use PGP encryption":["Cómo usar el cifrado PGP"],"Invalid password error while setting email client for Bridge":["Error de contraseña no válida al configurar el cliente de correo electrónico para Bridge"],"Login security notification alerts":["Notificación de alerta de seguridad de incio de sesión"],"Manage mailbox appearance":["Gestión de la apariencia del buzón"],"Mobile connectivity and synchronization":["Conexión y sincronización móviles"],"No, contact support":["No, contactar a soporte"],"Notifications":["Notificaciones"],"Other":["Otro"],"Problems with deleting messages":["Problemas con la eliminación de mensajes"],"Problems with moving messages":["Problemas para mover mensajes"],"Problems with read/unread message status":["Problemas con el estado de mensaje leído/sin leer"],"Proton Mail Bridge":["Proton Mail Bridge"],"Proton Mail settings":["Configuración de Proton Mail"],"Push notifications not arriving":["No llegan las notificaciones push"],"Sending and receiving messages":["Envío y recepción de mensajes"],"Sending and receiving messages limitations":["Limitaciones al envío y recepción de mensajes"],"Sending and receiving troubleshooting":["Solución de problemas de envío y recepción"],"Spam filtering, Allow and Block lists":["Filtro de spam y listas de permitidos y bloqueados"],"Sub-users and organizations":["Subusuarios y organizaciones"],"Thank you for your feedback":["Gracias por sus comentarios"],"Troubleshooting":["Solución de problemas"],"Verify custom domain records & anti-spoofing":["Verificación de registros de dominios personalizados y antisuplantación"],"What can we help with ?":["¿En qué podemos ayudar?"],"What if your domain records fail (TXT, MX, SPF, DKIM, DMARC)":["Qué ocurre si los registros de dominio fallan (TXT, MX, SPF, DKIM, DMARC)"],"What is encrypted on Proton Mail":["Qué es el cifrado en Proton Mail"],"Yes":["Sí"]},"support_modal_search_query":{"How to use a custom domain?":["¿Cómo utilizar un dominio personalizado?"],"Search query":["Consulta"]},"support_modal_search_result":{"Search result":["Resultado de la búsqueda"]},"support_modal_title":{"Blog search":["Búsqueda en el blog"],"Support search":["Búsqueda en la sección de soporte"]},"support_search_button":{"Search":["Buscar"]},"support_search_i_am_looking_for":{"I'm looking for":["Busco"]},"SupportForm":{"For a faster resolution, please report the issue from the Bridge app: Help > Report a problem.":["Para una resolución más rápida, reporte el problema desde la app Bridge: Ayuda > Reportar un problema."],"Information":["Información"]},"SupportForm:option":{"Account Security":["Seguridad de la cuenta"],"Contacts":["Contactos"],"Custom email domain":["Dominio de correo electrónico personalizado"],"Email delivery and Spam":["Entrega de correo electrónico y spam"],"Encryption":["Cifrado"],"Login and password":["Inicio de sesión y contraseña"],"Merge aliases and accounts":["Combinar alias y cuentas"],"Migrate to Proton":["Migrar a Proton"],"Notifications":["Notificaciones"],"Other":["Otros"],"Plans and billing":["Planes y facturación"],"Proton for Business":["Proton for Business"],"Sign up":["Regístrese"],"Storage":["Almacenamiento"],"Users, addresses, and identities":["Usuarios, direcciones e identidades"]},"SupportForm:optionIntro":{"Select a topic":["Seleccione un tema"]},"swiss_baseed_feature":{"Swiss based":["Con sede en Suiza"]},"Testimonial":{"Awards":["Premios"],"Customers":["Clientes"],"Featured":["Destacados"],"Go to testimonial source":["Ir a la fuente testimonial"],"Reviews":["Reseñas"],"Videos":["Videos"]},"Text":{"Find the plan that's right for you":["Encuentre el plan adecuado para usted"],"If you need help, check out our ${ supportLink }.":["Si necesita ayuda, consulte nuestra ${ supportLink }."],"The page you’re looking for might have been removed, or it could be an\nold link.":["Es posible que la página que busca haya sido eliminada o que sea un\nenlace antiguo."]},"Title":{"On this page":["En esta página"],"Related articles":["Artículos relacionados"],"Share ${ thisPage }":["Compartir ${ thisPage }"],"Thank you!":["¡Gracias!"],"this page":["esta página"]},"Tooltip":{"More information":["Más información"]},"tooltip_calendar":{"Create up to 20 custom & shareable encrypted calendars. On top of that, add up to 5 calendars from friends, family, colleagues, and organizations.":["Cree hasta 20 calendarios personalizados, compartibles y cifrados. Agregue hasta 5 calendarios de amigos, familiares, colegas y organizaciones."]},"tooltip_vpn":{"Access blocked content and browse privately. Includes ${ TOTAL_SERVERS }+ servers in ${ TOTAL_COUNTRIES }+ countries, highest VPN speed, ${ TOTAL_VPN_CONNECTIONS } VPN connections, worldwide streaming services, malware and ad-blocker, and more.":["Acceda a contenido bloqueado y navegue en privado. Tendrá a su disposición más de ${ TOTAL_SERVERS } servidores en más de ${ TOTAL_COUNTRIES } países, VPN de máxima velocidad, ${ TOTAL_VPN_CONNECTIONS } conexiones VPN, servicios de streaming en todo el mundo, bloqueadores de malware y de anuncios, y mucho más."],"Access blocked content and browse privately. Includes ${ TOTAL_SERVERS }+ servers in ${ TOTAL_COUNTRIES }+ countries, highest VPN speed, 10 VPN connections, worldwide streaming services, malware and ad-blocker, and more.":["Acceda a contenido bloqueado y navegue en privado. Tendrá a su disposición más de ${ TOTAL_SERVERS } servidores en más de ${ TOTAL_COUNTRIES } países, VPN de máxima velocidad, 10 conexiones VPN, servicios de streaming en todo el mundo, bloqueadores de malware y de anuncios, y mucho más."]},"version_history_label":{"Version history":["Historial de versiones"]},"version_history_tooltip":{"Store up to ${ versionHistoryNumber } versions of each file for up to ${ years } years":["Comparta hasta ${ versionHistoryNumber } versiones de cada archivo hasta durante ${ years } años"]},"VideoModal":{"Get started in 2 minutes":["Ponte en marcha en 2 minutos"]},"videosButtonLabel":{"Get started with videos":["Empezar con los videos"]},"vpn_features_link":{"View VPN plans":["Ver planes de VPN"]},"vpn_features_useCase":{"Access blocked content and browse privately":["Acceda a contenido bloqueado y navegue de forma privada"]}}},"unleashApi":"https://account.proton.me/api"};
// We need to import data (the framework context) from the server
// This Astro feature with define:vars works well but creates an inline script
// So we can't directly import the initFramework helper, we have to store the context
window.frameworkContext = frameworkContext;
})();
Proton Mail Bridge is a desktop application that runs in the background on your computer and encrypts and decrypts your mail as it enters and leaves your device. It allows for full integration of your Proton Mail account with email clients like Microsoft Outlook, Mozilla Thunderbird, and Apple Mail.
This document discusses how Bridge handles sensitive information, describes its potential attack vectors, and explains the security features that mitigate these attacks. (Note: This security model applies to the Bridge application for Linux, macOS, and Windows.)
This security model is technical in nature, but was written in plain language so that the average user can understand the important takeaways. You can also read more about what Proton Mail is and is not designed to protect you from in the Proton Mail threat model(new window).
As part of normal, day-to-day operations, Bridge must handle different types of data with varying levels of sensitivity. This data includes (but is not limited to):
User credentials and an access token for authentication with the Proton servers
Public and private keys for sending and reading messages
Encrypted messages, attachments, and metadata
We explain how Bridge secures this sensitive data in greater detail below.
Your passwords never leave your machine Users log in to Bridge, which in turn authenticates with the Proton Mail API using the Secure Remote Password protocol(new window). This authentication process ensures a user’s password never leaves their machine, and it generates an access token and a refresh token.
The access token is relatively short-lived and is used to authenticate any subsequent API requests; it is stored in the device’s memory. The refresh token is used to generate new access tokens and is stored securely in the operating system’s keychain (Windows Credentials Manager, macOS Keychain, or pass/gnome-keyring on Linux). The user’s hashed and salted mailbox password (used to decrypt their PGP keys) and Bridge password (used to connect an email client to Bridge) are also held in the operating system’s keychain.
Ensuring a secure connection to Proton servers Bridge communicates with the Proton Mail API over an encrypted TLS connection. It additionally employs TLS certificate public key pinning to ensure it only connects to trusted Proton Mail servers. If Bridge receives an untrusted public key, it will assume an unknown intermediary is pretending to be a Proton server and immediately warn the user.
Bridge never stores or shares a user’s PGP keys After the user logs in, Bridge downloads their encrypted, private PGP keys from the Proton servers and unlocks them. These keys are held in the device’s memory, never on disk. Whenever a user turns off their device, they wipe its memory. This makes it unlikely an attacker will be able to obtain a copy of a user’s PGP keys, even if they steal the user’s device. These keys are also never shared with other applications on your device and stay within Bridge’s memory space.
Bridge does not store decrypted message data When an IMAP client requests a message body or attachment, it is downloaded from the Proton servers as an encrypted PGP message, decrypted locally, and then transmitted to the IMAP client. Similar to the user’s PGP keys, Bridge does not permanently store any message bodies or attachments to disk, further reducing the amount of sensitive data available on the device.
Attack mitigation
Here we describe the potential attack vectors of Bridge and how we mitigate these attacks.
Reducing the threat of a MITM attack
As described, Bridge employs TLS certificate pinning, which mitigates the risk of a network-level man-in-the-middle (MITM) attack.
Furthermore, the content of messages sent from Bridge to Proton Mail users or external recipients using PGP has an additional layer of protection thanks to end-to-end encryption. This means Bridge encrypts the user’s message before it leaves their device. The message remains encrypted until it reaches the recipient’s device, which decrypts it. This prevents any third party, including Proton Mail, from accessing the content of a user’s message. Messages sent this way remain inaccessible because a user’s mailbox password never leaves their device and, thus, is never transmitted to an attacker.
Secure updates
Bridge on Windows and macOS includes a feature that allows it to self-update. The update process has additional safeguards in place to verify that only trusted versions of Bridge that are created and signed by Proton Mail are installed.
Bridge recommended use cases
Bridge is a unique tool when compared to the other Proton Mail apps. As such, there are specific cases in which it would be more practical and useful than other Proton Mail apps.
Below are some examples of recommended use cases for Bridge:
Offline editing If you find yourself without a stable Internet connection, you can use your favorite email client with Bridge to download emails while you do have good Internet access and then process them offline later. Most email clients will automatically send and receive your drafts once you are back online.
Offline backups of your emails are required If you need to have offline copies of your messages for whatever reason, Bridge is the easiest way to accomplish this. The Bridge app enables your IMAP/SMTP client to do this automatically if you choose to do so.
Add Proton Mail security to already known email clients If you or your staff do not feel confident learning how to use a new email service, Bridge lets you add Proton Mail encryption to your messages while continuing to use your favorite IMAP/SMTP email client. These clients include Outlook, Thunderbird, and Apple Mail, all applications that many people are familiar with. This means that once you set up Bridge, using it does not require any new training.
Bridge security model scope
No application is 100% secure, and no piece of software can protect its user against every potential threat. Proton Mail Bridge is engineered to provide additional protection to its users’ data, but certain conditions are outside of the scope of the security model.
User device security We assume users run the Bridge app in a safe environment. For instance, we assume that Bridge program files are installed to a location where normal (non-admin) users have no write privileges. Furthermore, we expect the user’s device to be free of any malicious software (keyloggers, screen recorders, memory scanners, etc.) that could access the device’s data in memory or on disk. Bridge, unfortunately, cannot secure your data if your device is already compromised.
Additionally, we assume that the IMAP/SMTP ports that the email client connects to are not exposed beyond the device that Bridge is running on. The Bridge application ignores all connections that do not originate from the localhost, and we assume the user will not attempt to circumvent this.
Bridge installer security We assume that the user securely downloaded the Bridge installer from our server (the server should present a valid and expected SSL certificate). For Windows and macOS, the operating system inspects the signatures on the installer file automatically before installation. It then displays the results to the user, which we assume they properly verify. We recommend Linux users refer to our support article on Verifying the Proton Mail Bridge package(new window) for instructions. If you download the Bridge application from an unauthorized source, we cannot guarantee the safety of the installer.
Our recommendations for keeping your device secure
We have invested heavily in the security of our Bridge app. You can help maximize the security of your own device by taking a few simple measures:
Encrypt your device’s hard drive. Windows(new window) and macOS(new window) devices all have built-in encryption systems, but you have to turn them on. Once you have encrypted your drive, write down your recovery code and store it in a secure place.
Enable your operating system’s antivirus protection, if available.
Ensure your network ports are secured by a firewall to prevent outside machines from connecting to them.
Do not install untrusted programs on your device. This includes unknown open source versions of Bridge. Downloading Bridge directly from Proton Mail(new window) is the safest option.
Do not open links or download attachments from untrusted senders.
Conclusion
Our first priority is always our users’ security. Our goal is to make it easy for anyone to protect their privacy by creating tools that apply advanced cryptography to their messages automatically. The Bridge tool was designed to add additional security to already existing IMAP/SMTP email clients. By keeping your device secure, you can use these email clients and still take charge of your data. Thank you for your support!
Proton Mail and Proton VPN are funded by community contributions. If you would like to support our development efforts, you can upgrade to a paid plan(new window). Thank you for your support.
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