Cryptography details

Crypto

Library

• SJCL

Key derivation

• PBKDF2 on 256 bits

Encryption/Decryption

• Galoi/Counter mode

Auth

• GMAC

Tag length (authentication data)

• 128 only

Process

Registration

• The passphrase is defined by the user
• A random string is generated, let's call it CEK
• The CEK is encrypted under the passphrase
• The CEK is stored in the database

Connection

• The user types his passphrase
• Get the CEK
• Try to decrypt the CEK under the passphrase
• if fail --> bad passphrase
• if success --> store it locally

Encryption & Decryption

Key derivation

• Check if the CEK is stored locally (if not, log out the user)
• Generate salt on 128 bits
• Proceed to a key derivation under PBKDF2 with the CEK and the salt (strengthen by a factor of 7000 and 256 bits key size)

Encryption process

• Generate the initialization vector on 128 bits for every chunk
• Generate authentication data on 128 bits
• Use GCM, encrypt the chunk
• Encapsulate the auth' data + salt + initialization vector + encrypted content (=chunk)

Decryption

• Do the inverse processs

"Passphrase" change

• Check if the CEK is stored locally (if not, log out the user)
• Encrypt the CEK under the new re-defined typed by the user
• Send the CEK to the servers to store it in the database

Reset the CEK and the passphrase

• Delete all the files and folders of the user
• Generate a new CEK
• Encrypt the CEK under the passphrase
• Send the CEK to the servers to store it in the database

File Sharing

~~ coming soon ~~