Saturday, May 18, 2024

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 industrial and public sector organizations a further layer of confidentiality and knowledge integrity safety past the prevailing encryption supplied by default in Workspace. When CSE is enabled, electronic mail messages are protected utilizing encryption keys which can be totally underneath the client’s management. The info is encrypted on the consumer gadget earlier than it’s despatched to Google servers that do not need entry to the encryption keys, which implies the information is indecipherable to us–we now have no technical skill to entry it. The whole course of occurs within the browser on the consumer gadget, with out the necessity to set up desktop purposes or browser extensions, which implies that customers get the identical intuitive productiveness and collaboration experiences that they take pleasure in with Gmail immediately. 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 known as, Key Entry Management Record Service (KACLS), that’s used throughout all important Workspace purposes. Then, we labored instantly with prospects 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 known as by the CSE-enabled Workspace shoppers. We’ve a number of companions offering software program implementations of the KACLS API that can be utilized by our prospects. 

At a excessive stage, Workspace consumer code takes benefit of envelope encryption to encrypt and decrypt the consumer content material on the consumer with a Information Encryption Key (DEK) and leverage the KACLS to encrypt and decrypt the DEK. So as to present separation of obligation, we use the client’s OpenID Join (OIDC) IdP to authenticate end-users and supply a JSON Net Token assertion with a declare figuring out the consumer (3P_JWT). For each encryption/decryption request despatched to KACLS, the applying (e.g. Gmail) offers a JSON Net 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 consumer’s consumer gadget.

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 onerous at work over a number of years to ship to our prospects the flexibility to have their knowledge protected with client-side encryption. This journey required us to work carefully with prospects and companions to supply a functionality that was safe, straightforward to make use of, intuitive and simply deployable. It was additionally vital for CSE to work seamlessly throughout the Workspace merchandise: you possibly can create a Meet CSE scheduled assembly in Calendar CSE and follow-up with Gmail CSE emails containing hyperlinks to Drive CSE information.

Consumer-side encryption in Gmail was constructed with openness and interoperability in thoughts. The underlying know-how getting used is S/MIME, an open commonplace for sending encrypted messages over electronic mail. S/MIME is already supported in most enterprise electronic mail shoppers, 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 consumer are included within the consumer’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 consumer. The consumer’s personal keys are saved safe underneath 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 hold the personal key on the gadget, to maintain them as secure as doable. As a substitute, we prolonged our KACLS API to help uneven encryption and signature operations. This permits our prospects to centrally provision and allow S/MIME, on the KACLS, for all their customers with out having to deploy certificates individually to every consumer gadget.

CSE in Gmail makes use of the end-user’s consumer current cryptographic functionalities (Net Crypto API for net browsers for example) 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 consumer flows:

When sending an electronic mail, the Gmail consumer generates a MIME message, encrypts the message with a random Information Encryption Key (DEK) then makes use of the recipients’ public keys to encrypt the DEK, calls KACLS (with the consumer authenticated by buyer’s IdP and approved by Google) to digitally signal content material and eventually sends the authenticated and encrypted S/MIME message, which incorporates each the encrypted electronic mail and the encrypted DEK, to Google servers for supply to the recipients. Under is an animated screenshot exhibiting the consumer interface of Gmail when utilizing CSE.


When receiving an electronic mail, Gmail will confirm that the digital signature of the e-mail is legitimate and matches the sender’s id, 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 consumer 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 applying

Workspace already makes use of the most recent cryptographic requirements to encrypt all knowledge 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 electronic mail service suppliers. CSE in Gmail, nonetheless, offers a further layer of safety for delicate content material. The safety of Gmail CSE is paramount to us, and we developed new extra mechanisms to make sure CSE content material can be locked right into a safe container. On the internet, we now have been leveraging iframe origin isolation, strict postMessage API, and Content material Safety Coverage to guard the consumer’s delicate knowledge. These safety controls present a number of layers of security to make sure that CSE content material stays remoted from the remainder of the applying. See this simplified diagram masking the isolation defending CSE emails throughout composition or show.

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

CSE in Gmail makes use of S/MIME to encrypt and digitally signal emails utilizing public keys provided by prospects, which add a further stage of confidentiality and integrity to emails. That is executed with intensive safety controls to guard consumer knowledge confidentiality, but additionally transparently built-in in Gmail UI to please our customers. Nonetheless our work isn’t executed, and we’re actively partnering with Google Analysis to additional develop client-side capabilities. You’ll be able to see a few of our progress on this subject with our presentation on the RSA Safety Convention final yr the place we offered perception into the challenges and the sensible methods to supply superior capabilities, resembling AI-driven phishing safety for CSE.

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