You are currently viewing Google On-line Safety Weblog: Gmail client-side encryption: A deep dive

Google On-line Safety Weblog: Gmail client-side encryption: A deep dive

In February, we expanded Google Workspace client-side encryption (CSE) capabilities to incorporate Gmail and Calendar along with Drive, Docs, Slides, Sheets, and Meet.

CSE in Gmail was designed to supply business and public sector organizations a further layer of confidentiality and information integrity safety past the prevailing encryption provided by default in Workspace. When CSE is enabled, e-mail messages are protected utilizing encryption keys which can be absolutely beneath the shopper’s management. The info is encrypted on the shopper machine earlier than it’s despatched to Google servers that would not have entry to the encryption keys, which implies the information is indecipherable to us–we’ve no technical potential to entry it. The complete course of occurs within the browser on the shopper machine, with out the necessity to set up desktop purposes or browser extensions, which signifies that customers get the identical intuitive productiveness and collaboration experiences that they get pleasure from with Gmail as we speak. Let’s take a deeper look into the way it works.

How we constructed Consumer-side Encryption for Workspace

We invented and designed a brand new service referred to as, Key Entry Management Listing Service (KACLS), that’s used throughout all important Workspace purposes. Then, we labored straight with clients and companions to make it safe, dependable, and easy to deploy. KACLS performs cryptographic operations with encryption keys after validating end-user authentication and authorization. It runs in a buyer’s managed surroundings and offers the important thing administration API referred to as by the CSE-enabled Workspace purchasers. Now we have a number of companions offering software program implementations of the KACLS API that can be utilized by our clients. 

At a excessive stage, Workspace shopper code takes benefit of envelope encryption to encrypt and decrypt the person content material on the shopper with a Knowledge Encryption Key (DEK) and leverage the KACLS to encrypt and decrypt the DEK. As a way to present separation of responsibility, we use the shopper’s OpenID Join (OIDC) IdP to authenticate end-users and supply a JSON Internet Token assertion with a declare figuring out the person (3P_JWT). For each encryption/decryption request despatched to KACLS, the appliance (e.g. Gmail) offers a JSON Internet Token assertion with a declare authorizing the present end-user operation (G_JWT). KACLS validates these authentication and authorization tokens earlier than returning, for instance, a decrypted DEK to the person’s shopper machine.

Extra particulars on KACLS can be found in Google Workspace Encryption Whitepaper and CSE reference API.

How we constructed CSE into Gmail

Google Workspace Engineering groups have been exhausting at work over a number of years to ship to our clients the power to have their information protected with client-side encryption. This journey required us to work carefully with clients and companions to supply a functionality that was safe, straightforward to make use of, intuitive and simply deployable. It was additionally necessary for CSE to work seamlessly throughout the Workspace merchandise: you’ll be able to create a Meet CSE scheduled assembly in Calendar CSE and follow-up with Gmail CSE emails containing hyperlinks to Drive CSE recordsdata.

Consumer-side encryption in Gmail was constructed with openness and interoperability in thoughts. The underlying know-how getting used is S/MIME, an open normal for sending encrypted messages over e-mail. S/MIME is already supported in most enterprise e-mail purchasers, so customers are capable of talk securely, outdoors of their area, no matter what supplier the recipient is utilizing to learn their mail, with out forcing the recipients to log right into a proprietary portal. S/MIME makes use of uneven encryption. The general public key and the e-mail of every person are included within the person’s S/MIME certificates. Equally to TLS used for HTTPS, every certificates is digitally signed by a series of certificates authorities as much as a broadly trusted root certificates authority. The certificates acts as a digital enterprise card, enabling anybody getting it to encrypt emails for that person. The person’s personal keys are stored safe beneath buyer management and are utilized by customers for decryption of incoming emails and digital signature of outgoing emails.

We determined to leverage the CSE paradigm used for Drive CSE and never preserve the personal key on the machine, to maintain them as protected as attainable. As an alternative, we prolonged our KACLS API to help uneven encryption and signature operations. This allows our clients to centrally provision and allow S/MIME, on the KACLS, for all their customers with out having to deploy certificates individually to every person machine.

CSE in Gmail makes use of the end-user’s shopper present cryptographic functionalities (Internet Crypto API for net browsers as an illustration) to carry out native encryption operations and run client-side code to carry out all S/MIME message era.

Now let’s cowl the detailed person flows:

When sending an e-mail, the Gmail shopper generates a MIME message, encrypts the message with a random Knowledge Encryption Key (DEK) then makes use of the recipients’ public keys to encrypt the DEK, calls KACLS (with the person authenticated by buyer’s IdP and licensed by Google) to digitally signal content material and at last sends the authenticated and encrypted S/MIME message, which accommodates each the encrypted e-mail and the encrypted DEK, to Google servers for supply to the recipients. Under is an animated screenshot displaying the person interface of Gmail when utilizing CSE.


When receiving an e-mail, Gmail will confirm that the digital signature of the e-mail is legitimate and matches the sender’s identification, which protects the e-mail towards tampering. Gmail will belief digital identities signed by Root CA PKI in addition to customized area configurations. The Gmail shopper will name KACLS (with the authentication and authorization JWT) to decrypt the e-mail encryption key, then can decrypt the e-mail and render it to the end-user.

How we shield the appliance

Workspace already makes use of the newest cryptographic requirements to encrypt all information at relaxation and in transit between its services for all companies. Moreover, Gmail makes use of Transport Layer Safety (TLS) by default for communication with different e-mail service suppliers. CSE in Gmail, nevertheless, offers a further layer of safety for delicate content material. The safety of Gmail CSE is paramount to us, and we developed new further mechanisms to make sure CSE content material can be locked right into a safe container. On the net, we’ve been leveraging iframe origin isolation, strict postMessage API, and Content material Safety Coverage to guard the person’s delicate information. These safety controls present a number of layers of security to make sure that CSE content material stays remoted from the remainder of the appliance. See this simplified diagram overlaying the isolation defending CSE emails throughout composition or show.

What’s subsequent for Consumer-side encryption and why it’s necessary 

CSE in Gmail makes use of S/MIME to encrypt and digitally signal emails utilizing public keys equipped by clients, which add a further stage of confidentiality and integrity to emails. That is carried out with intensive safety controls to guard person information confidentiality, but additionally transparently built-in in Gmail UI to please our customers. Nevertheless our work isn’t carried out, and we’re actively partnering with Google Analysis to additional develop client-side capabilities. You possibly can see a few of our progress on this subject with our presentation on the RSA Safety Convention final 12 months the place we supplied perception into the challenges and the sensible methods to supply superior capabilities, comparable to AI-driven phishing safety for CSE.

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