The Most Secure Cloud Storage Provider Anton Titov CTO CyberCon, June 2018, Sofia

Client-side encryption Zero-knowledge privacy Multi-layer protection Absolute Security with pCloud Crypto Client-side encryption Only the user has access to the encrypted content Zero-knowledge privacy pCloud does not know what is saved in Crypto Folders Multi-layer protection Additional protection layers & keys pCloud Crypto Hacking Challenge with $100,000 award. For 6 months 2,800+ hackers - Berkeley, Boston, MIT and 523 other organizations None of them succeeded.

Mission Client-side encrypted cloud storage Accessible from multiple software clients / platforms All user needs to access encrypted data are account credentials and encryption passphrase Efficient read/write random access

Everybody do encryption, don't they? Encryption of in-transit data Encryption of stored data with provider's keys Client-side encryption

Still, it should not be that hard, right? What is actually encryption? What is authentication? Encryption and authentication of data connection - fairly trivial. Block device (hard drive) encryption - fairly trivial. Authentication may degrade performance, but you can live without it. Encryption of randomly accessible data - fairly trivial, authentication is however tricky.

How to authenticate a file as a whole? Split file into blocks of some size, say 4Kb Use a Merkle tree to authenticate the file Since we are working with disk storage, don't use a binary Merkle tree, but say 256-way one Files with reasonable size will have a tree-depth of 2-4 levels Wouldn't it be great to also have a Merkle tree of directory structure?

Technological overview Each user has 4096 bit RSA key, private encrypted with AES256 key derived from passphrase with PBKDF2, public and encrypted private parts stored in the cloud Each folder and each file has its own AES256 and HMAC-SHA512 key, encrypted with RSA and stored in the cloud Folder keys used to encrypt file names and sign keys of in-folder contents File keys encrypt and authenticate the file data

So the private key is actually stored in the cloud? Yes, but it is in turn encrypted There are alternatives but those are slow and messy

Future work: Share-Able encryption 24/7 Access to files We don't really need RSA in the picture now Big challenge: trust, MITM Just encrypt every folder/file key with public keys of all users that have access Linear scaling by number of users is not ideal, but public RSA operations are ~100 faster than private ones anyway Collaboration

Anton Titov, CTO anton@pCloud.com Thank You Questions? Anton Titov, CTO anton@pCloud.com