Cloud photo services are widely used for persistent, convenient, and often free photo storage, which is especially useful for mobile devices. As users store more and more photos in the cloud, significant privacy concerns arise because even a single compromise of a user's credentials give attackers unfettered access to all of the user's photos. We have created Easy Secure Photos (ESP) to enable users to protect their photos on cloud photo services such as Google Photos. ESP introduces a new client-side encryption architecture that includes a novel format-preserving image encryption algorithm, an encrypted thumbnail display mechanism, and a usable key management system. ESP encrypts image data such that the result is still a standard format image like JPEG that is compatible with cloud photo services. ESP efficiently generates and displays encrypted thumbnails for fast and easy browsing of photo galleries from trusted user devices. ESP's key management makes it simple to authorize multiple user devices to view encrypted image content via a process similar to device pairing, but using the cloud photo service as a QR code communication channel. We have implemented ESP in a popular Android photos app for use with Google Photos and demonstrate that it is easy to use and provides encryption functionality transparently to users, maintains good interactive performance and image quality while providing strong privacy guarantees, and retains the sharing and storage benefits of Google Photos without any changes to the cloud service. CCS CONCEPTS• Security and privacy → Key management; Public key encryption; Mobile and wireless security; Usability in security and privacy; Privacy protections; Software security engineering; Distributed systems security; • Computer systems organization → Cloud computing; • Human-centered computing → Ubiquitous and mobile devices; • Information systems → Web services.

Email privacy is of crucial importance. Existing email encryption approaches are comprehensive but seldom used due to their complexity and inconvenience. We take a new approach to simplify email encryption and improve its usability by implementing receiver-controlled encryption: newly received messages are transparently downloaded and encrypted to a locally-generated key; the original message is then replaced. To avoid the problem of moving a single private key between devices, we implement per-device key pairs: only public keys need be synchronized via a simple verification step. Compromising an email account or server only provides access to encrypted emails. We implemented this scheme on several platforms, showing it works with PGP and S/MIME, is compatible with widely used mail clients and email services including Gmail, has acceptable overhead, and that users consider it intuitive and easy to use.

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