all-in-one privacy solution":["Proton Unlimited est une solution tout-en-un respectueuse de la vie privée"],"Black Friday":["Black Friday"],"No ads. Privacy by default.":["Aucune publicité, le respect de la vie privée comme règle absolue"],"People before profits":["Les individus passent avant les profits"],"Security through transparency":["Notre engagement de transparence"],"The best Proton Mail ${ BLACK_FRIDAY } deals":["Les meilleures offres ${ BLACK_FRIDAY } de Proton Mail"],"The world’s only community- supported email service":["La seule messagerie au monde soutenue par la communauté"]},"specialoffer:limited":{"${ hours } hour":["${ hours } heure","${ hours } heures"],"${ hoursLeft }, ${ minutesLeft } and ${ secondsLeft } left":["Temps restant : ${ hoursLeft }, ${ minutesLeft }, ${ secondsLeft }"],"${ minutes } minute":["${ minutes } minute","${ minutes } minutes"],"${ seconds } second":["${ seconds } seconde","${ seconds } secondes"],"Limited time offer":["Offre à durée limitée"]},"specialoffer:listitem":{"Create multiple addresses":["Créez plusieurs adresses"],"Hide-my-email aliases":["Alias « hide-my-email »"],"Quickly unsubscribe from newsletters":["Désabonnez-vous rapidement des newsletters"],"Use your own domain name":["Utilisez votre propre nom de domaine"]},"specialoffer:logos":{"As featured in":["Ils en parlent"]},"specialoffer:metadescription":{"Get an encrypted email that protects your privacy":["Choisissez une messagerie électronique chiffrée qui protège votre vie privée"]},"specialoffer:metatitle":{"Proton Mail Black Friday Sale - Up to 40% off":["Offre Proton Mail Black Friday - Jusqu'à 40 % de réduction"]},"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.":["Obtenez jusqu'à 40 % de réduction sur les abonnements Proton Mail à l'occasion du Black Friday. Profitez d'offres exceptionnelles sur nos abonnements de messagerie électronique sécurisée et chiffrée de bout en bout."]},"specialoffer:newmetatitle":{"Proton Mail Black Friday sale | Up to 40% off secure email":["Offre Black Friday Proton Mail | Jusqu'à 40 % de réduction"]},"specialoffer:note":{"* Billed at ${ TOTAL_SUM } for the first year":["* Facturé ${ TOTAL_SUM } pour la première année"],"*Billed at ${ TOTAL_SUM } for the first 2 years":["*Facturé ${ TOTAL_SUM } pour les 2 premières années"],"30-day money-back guarantee":["Garantie satisfait ou remboursé pendant 30 jours"],"Billed at ${ TOTAL_SUM } for the first 2 years":["Facturé ${ TOTAL_SUM } pour les 2 premières années"],"Billed at ${ TOTAL_SUM } for the first year":["Facturé ${ TOTAL_SUM } pour la première année"],"You save ${ SAVE_SUM }":["Vous économisez ${ SAVE_SUM }"]},"specialoffer:off":{"${ DISCOUNT } off":["-${ DISCOUNT }"],"${ PERCENT_OFF } off":["-${ PERCENT_OFF }"]},"specialoffer:testimonial":{"I love my ProtonMail":["J'adore mon ProtonMail"],"My favorite email service":["Ma messagerie électronique préférée"],"Thanks Proton for keeping us all safe in the complicated internet universe.":["Merci Proton de nous garder en sécurité dans l'univers complexe d'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":["Vous avez ce pour quoi vous payez. Avec les Big Tech, si vous ne payez rien, vous êtes utilisé. J'ai arrêté d'utiliser Gmail et je suis passée @ProtonMail"]},"specialoffer:time":{"Days":["Jours"],"Hours":["Heures"],"Min":["Min"]},"specialoffer:title":{"And much more":["Avec en plus"],"Make your inbox yours":["Votre boite de réception sur mesure"],"Safe from trackers":["À l'abri des traqueurs"],"Stay organized":["Bien organisé"],"Black Friday email deals":["Offres Black Friday pour la messagerie électronique"],"Don’t just take our word for it":["Ce qu'en disent nos utilisateurs"],"Our story":["Notre histoire"],"Transfer your data from Google in one click":["Transférez vos données depuis Google en un 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.":["Accédez aux contenus bloqués et naviguez en toute confidentialité. Comprend plus de ${ TOTAL_SERVERS } serveurs répartis dans plus de ${ TOTAL_COUNTRIES } pays, la possibilité de connecter jusqu'à 10 appareils, l'accès aux services de streaming dans le monde entier, un bloqueur de logiciels malveillants et de publicités et d'autres fonctionnalités."],"Easily share your calendar with your family, friends or colleagues, and view external calendars.":["Partagez facilement votre calendrier avec votre famille, vos amis ou collègues et consultez des calendriers externes."],"Includes support for 1 custom email domain, 10 email addresses, 10 hide-my-email aliases, calendar sharing, and more.":["Comprend la prise en charge de 1 domaine de messagerie personnalisé, de 10 adresses e-mail, de 10 alias « hide-my-email », du partage de calendriers et bien d'autres fonctionnalités."],"Includes support for 3 custom email domains, 15 email addresses, unlimited hide-my-email aliases, calendar sharing, and more.":["Comprend la prise en charge de 3 domaines de messagerie personnalisés, de 15 adresses e-mail, d'un nombre illimité d'alias « hide-my-email », du partage de calendriers et bien d'autres fonctionnalités."],"Manage up to 25 calendars, mobile apps, secured with end-to-end encryption, 1-click calendar import from Google, and more.":["Jusqu'à 25 calendriers, des applications mobiles, la sécurité avec le chiffrement de bout en bout, l'importation de calendrier en un clic depuis Google..."]},"Status Banner":{"At the moment we are experiencing issues with the Proton VPN service":["Nous rencontrons actuellement des problèmes avec le service Proton VPN."],"Learn more":["En savoir plus"]},"Status banner":{"Learn more":["En savoir plus"],"Please note that at the moment we are experiencing issues with the ${ issues[0] } service.":["Nous rencontrons actuellement des problèmes avec le service ${ issues[0] }."],"We are experiencing issues with one or more services at the moment.":["Nous rencontrons actuellement des problèmes avec un ou plusieurs services."]},"suggestions":{"Suggestions":["Suggestions"]},"Support":{"Sub category":["Sous-catégorie","Sous-catégories"]},"Support article":{"${ readingTime } min":["${ readingTime } minute","${ readingTime } minutes"],"Category":["Catégorie","Catégories"],"Didn’t find what you were looking for?":["Vous ne trouvez pas ce que vous cherchez ?"],"General contact":["Contact - Général"],"Get help":["Obtenir de l'aide"],"Legal contact":["Contact - Juridique"],"Media contact":["Contact - Média"],"Partnerships contact":["Contact - Partenariats"],"Reading":["Lecture"]},"Support categories":{"Browse Proton product support":["Parcourez le support produit Proton"]},"Support category":{"There is no article in this category yet.":["Il n'y a pas encore d'article dans cette catégorie."]},"Support troubleshooting":{"--- Select ---":["--- Sélectionner ---"],"App version":["Version de l'application"],"Browser":["Navigateur"],"Check if this helps":["Vérifiez si cela vous aide."],"Choose a category for your question":["Choisissez une catégorie pour votre question"],"Choose a product":["Choisir un produit"],"Did this solve your issue ?":["Cela a-t-il résolu votre problème ?"],"Faster assistance is just a few clicks away — please make your selections":["Il suffit de quelques clics pour obtenir une assistance plus rapide, faites votre sélection."],"No, contact support":["Non, contacter le support"],"Proton account":["Compte Proton"],"Proton Bridge":["Proton Bridge"],"Proton Calendar":["Proton Calendar"],"Proton Drive":["Proton Drive"],"Proton for Business":["Proton for Business"],"Proton Mail":["Proton Mail"],"Proton Pass":["Proton Pass"],"Proton VPN":["Proton VPN"],"Thank you for your feedback":["Nous vous remercions pour votre commentaire."],"Troubleshooting":["Dépannage"],"What can we help with ?":["Comment pouvons-nous vous aider ?"],"Yes":["Oui"]},"support_modal_search_query":{"Search query":["Recherche"]},"support_search_button":{"Search":["Rechercher"]},"support_search_i_am_looking_for":{"I'm looking for":["Je recherche des informations sur..."]},"SupportForm":{"For a faster resolution, please report the issue from the Bridge app: Help > Report a problem.":["Pour que le problème soit résolu plus rapidement, vous pouvez le signaler à partir de l'application Bridge : Aide > Signaler un bug."],"Information":["Informations"]},"SupportForm:option":{"Account Security":["Sécurité du compte"],"Contacts":["Contacts"],"Custom email domain":["Domaine de messagerie personnalisé"],"Email delivery and Spam":["Distribution des messages et indésirables/spam"],"Encryption":["Chiffrement"],"Login and password":["Identifiant et mot de passe"],"Merge aliases and accounts":["Fusion des alias et des comptes"],"Migrate to Proton":["Migration vers Proton"],"Notifications":["Notifications"],"Other":["Autre"],"Plans and billing":["Abonnements et facturation"],"Proton for Business":["Proton for Business"],"Sign up":["Inscription"],"Storage":["Espace de stockage"],"Users, addresses, and identities":["Utilisateurs, adresses et identités"]},"SupportForm:optionIntro":{"Select a topic":["Choisissez un sujet"]},"swiss_baseed_feature":{"Swiss based":["Basé en Suisse"]},"Testimonial":{"Awards":["Récompenses"],"Customers":["Clients"],"Featured":["Ils en parlent"],"Go to testimonial source":["Accéder aux commentaires"],"Reviews":["Avis"],"Videos":["Vidéos"]},"Text":{"Find the plan that's right for you":["Trouvez l'abonnement adapté à vos besoins"],"If you need help, check out our ${ supportLink }.":["Si vous avez besoin d'aide, consultez notre ${ supportLink }."],"The page you’re looking for might have been removed, or it could be an\nold link.":["La page recherchée a peut-être été retirée ou le lien utilisé n'est plus valide."]},"Title":{"On this page":["Sur cette page"],"Related articles":["Articles similaires"],"Share ${ thisPage }":["Partagez ${ thisPage }"],"Thank you!":["Merci !"],"this page":["cette page"]},"Tooltip":{"More information":["Plus d'informations"]},"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.":["Créez jusqu'à 20 calendriers chiffrés personnalisés et partageables. Ajoutez jusqu'à 5 calendriers d'amis, de membres de votre famille, de collègues ou d'organisations."]},"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.":["Accédez aux contenus bloqués et naviguez en toute confidentialité. Comprend plus de ${ TOTAL_SERVERS } serveurs répartis dans plus de ${ TOTAL_COUNTRIES } pays, la vitesse VPN la plus élevée, ${ TOTAL_VPN_CONNECTIONS } connexions VPN, l'accès aux services de streaming dans le monde entier, un bloqueur de logiciels malveillants et de publicités et d'autres fonctionnalités."],"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.":["Accédez aux contenus bloqués et naviguez en toute confidentialité. Comprend plus de ${ TOTAL_SERVERS } serveurs répartis dans plus de ${ TOTAL_COUNTRIES } pays, la vitesse VPN la plus élevée, 10 connexions VPN, l'accès aux services de streaming dans le monde entier, un bloqueur de logiciels malveillants et de publicités et d'autres fonctionnalités."]},"version_history_label":{"Version history":["Historique des versions"]},"version_history_tooltip":{"Store up to ${ versionHistoryNumber } versions of each file for up to ${ years } years":["Conservez jusqu'à ${ versionHistoryNumber } versions de chaque fichier pendant ${ years } ans."]},"vpn_features_link":{"View VPN plans":["Voir les abonnements VPN"]},"vpn_features_useCase":{"Access blocked content and browse privately":["Accédez aux contenus bloqués et naviguez en toute confidentialité"]}}},"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;
})();
On 1 December 2021, we began receiving sporadic reports of delivery failures from proton.me addresses to Gmail. This corresponded with a dramatic decline in proton.me’s domain reputation as seen via Gmail Postmaster Tools and an increase in sending from known bad IP addresses.
It was clear both from the bad sending IPs (mostly in Russia) and our own metrics that the spam emails damaging Proton Mail’s domain reputation were not coming from our servers. However, the Postmaster Tools indicated that all emails being received by Gmail from proton.me were “fully authenticated”, including the fraudulent ones.
This, in turn, caused the fraudulent emails to feed into Google’s algorithm for determining domain reputation and lowered it enough that the deliverability of legitimate emails from our servers was affected as well.
We suspected a DKIM(new window) replay attack, where a single spam email originally sent from Proton Mail was being resent to many Gmail users in an attempt to exploit our deliverability and reputation to get around Google’s anti-spam measures. At one point, roughly 98% of the emails Gmail received that claimed to be from Proton Mail were actually spam, meaning the spammers were sending an amount of emails that was equivalent to 50 times our normal outgoing traffic to Google.
We immediately rotated our DKIM signing key to (temporarily) prevent the emails from passing DKIM and contacted Google’s counter-abuse team, who quickly implemented a fix to Gmail’s spam filters and restored legitimate email delivery.
Emails sent from proton.me, proton.me/mail, and custom domains were not affected by this issue.
How DKIM replay attacks work
Before we can explain how this happened, we first need to outline how emails are structured, delivered, and authenticated on the internet.
Emails are MIME (Multipurpose Internet Mail Extensions) messages, consisting of headers(new window) and sections that contain the message body and possibly attachments. The headers contain some fields that will be familiar to any email user (To, CC, From, Subject) but also hidden information that is used to authenticate the email.
However, none of the headers are actually used to route the email to its final destination. The recipient and sender of the email are specified separately as part of the email envelope, which is a very suitable metaphor. If the email message, including its headers, is equivalent to a paper letter, then the email envelope in which the “letter” is placed contains the recipient and return addresses, like a real envelope.
The key point is that the recipient on the envelope does not have to match any recipient in the To or CC headers — typical examples of this are emails sent via BCC or addressed to “undisclosed recipients”.
Perhaps even more surprisingly, the envelope sender does not have to match the email From header. This also has a legitimate purpose — mass mailings often specify a different “return address” than the From header to analyze deliverability problems or use third-party services to send emails. This flexibility is also important for enabling users to forward messages from one mailbox to another.
These return addresses are authenticated via SPF (Sender Policy Framework)(new window), which authorizes the sending of messages by specific servers or IP addresses using special DNS records. But this only validates the server sending the email; it does not ensure that the email’s content has not been tampered with. For that, we need DKIM (Domain Keys Identified Mail)(new window).
DKIM also uses special DNS records, but rather than a list of IP addresses, these records contain keys used to sign the email content and certain associated headers. The resulting cryptographic signature is appended to the message as a special header, and the recipient mail server or client can verify this signature against the email content on delivery. But the DKIM domain in the signature can also be different from the one in the From header in the message itself. If the DKIM signature is verified, this only confirms that the message went through the signing domain’s mail servers and has not been modified since, not that the message originated from where it claims.
To actually verify that the domain in the From header sent the message, we need DMARC (Domain-based Message Authentication, Reporting, and Conformance)(new window). To pass DMARC, an email must pass either SPF or DKIM, and the domain in the From header must be “aligned” with the corresponding SPF or DKIM domain. The From header is what the user ultimately sees, so DMARC is a critical part of ensuring that an email originated from where it claims it did as it is the only policy that connects the From header to either the sending or signing domain.
Now let’s return to the attack. The reason that DKIM replay attacks work and why Gmail considered those replayed spam mails “authenticated” comes down to the fact that DMARC requires DKIM or SPF alignment, but not both. The replayed message itself had a valid DKIM signature from proton.me, which meant it passed DMARC. This message was then sent enough times that it influenced proton.me’s domain reputation in Gmail’s system, eventually becoming low enough to affect deliverability for legitimate email.
How we prevent replay attacks
The fact that DMARC passes if either the DKIM domain or the SPF domain align with the From domain is a feature of the specification, not a bug. In particular, it enables email forwarding and allows email sending by trusted third parties. However, for email service providers, such as Proton, Gmail, or Yahoo, it also enables these kinds of replay attacks, as any user can send an email, get it signed by the corresponding domain, then resend it with the signature intact.
This is one reason that Proton and other email providers invest heavily in their own anti-spam technology and systems. These systems are complex and often rely on complicated heuristics to separate spam from legitimate email. In this case, the attackers found a vulnerability in Gmail’s anti-spam system and were able to exploit it.
We appreciate Google’s responsiveness in addressing the issue.
How you can prevent domain impersonation on your domain
DKIM replay attacks are an issue primarily for email service providers or other organizations that offer email addresses on a shared domain. However, email authentication attacks in general are a risk for any organization. Here are some tips to help you ensure no one else can impersonate your domain or use it to send fraudulent messages.
Set up SPF, DKIM, and DMARC – Although imperfect, these policies are key to ensuring that your emails are delivered and resistant to being spoofed(new window). If you use Proton to host your domain, our domain setup wizard will explain how to set it up and protect it from being spoofed.
Rotate your DKIM keys regularly – Rotating our DKIM keys allowed us to quickly stop the attack and buy time for the permanent solution. Although tedious and risky to do manually, Proton’s DKIM key management system(new window) allowed us to easily do this in minutes, and this system is the same system used for all domains hosted at Proton. The system also automatically rotates keys regularly to reduce the risk of key compromise.
Oversign From, To, and CC headers – Most DKIM implementations always sign the From, To, and CC headers if they are present in an email, preventing them from being modified if the message is resent. However, if these headers are missing, they are often unsigned, opening the door to replay attacks with forged headers that make the fraudulent emails seem legitimate. Oversigning mitigates these attacks by signing these sensitive headers in all cases, even if they are blank. If you use Proton to send your email, this oversigning is done for you automatically by our mail servers.
Be careful of subdomains – If you use CNAME records to delegate parts of your website to third parties, you may be also allowing these third parties to send email on behalf of your main domain. This is because, by default, DMARC considers domains aligned if they have a parent-child relationship — that is, sub.example.com aligns with example.com. You can force exact match alignment for SPF, DKIM, or both with the aspf and adkim options in your DMARC policy. However, be aware that this can affect third-party mailing service integrations.
A lot happens after you click Send in Proton Mail
If we’re doing everything correctly on our end, email delivery seems as easy as a single click, but the truth is that it relies on a complex web of interlocking, interdependent policies. Events like this replay attack demonstrate just how complicated it can be to verify something as seemingly simple as “Who sent this email?”
At Proton Mail, we are constantly investigating new protocols and policies to ensure that the millions of emails sent using our platform every day are delivered reliably and securely. We also continuously monitor incoming mail to ensure our authentication checking has been optimized and we have systems and analysts in place 24/7 to mitigate spam and phishing attacks.
This is a vital part of creating an internet where privacy is the default, and we could not do it without the support of the Proton community. Thank you.
Une communication sécurisée et fluide est la base de toute entreprise. Alors que
de plus en plus d’organisations sécurisent leurs données avec Proton, nous avons
considérablement élargi notre écosystème avec de nouveaux produits et services,
de notre
En matière de cybersécurité, un terme qui revient souvent est l’attaque par
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la finesse, mais utilise plutôt la puissance de calcul brute pour craquer la
sécurité ou même
Note : les liens dans cet article renvoient à des contenus en anglais.
La section 702 du Foreign Intelligence Surveillance Act est devenue tristement
célèbre comme justification juridique permettant à des agences fédérales telles
que la NSA, la CIA
En réponse au nombre croissant de fuites de données, Proton Mail propose une
fonctionnalité aux abonnés payants appelée surveillance du dark web. Notre
système vérifie si vos identifiants ou autres données ont été divulgués sur des
marchés illégaux e
Votre adresse e-mail est votre identité en ligne et vous la partagez chaque fois
que vous créez un nouveau compte pour un service en ligne. Cette solution est
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Notre mission chez Proton est de contribuer à l’avènement d’un internet qui
protège votre vie privée par défaut, sécurise vos données et vous donne la
liberté de choix.
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