Eu usei o Google para encontrar isso .
Data Encryption - When using web apps on a Chromebook, all important data is stored safely in the cloud. Certain kinds of files, like downloads, cookies, and browser cache files, may still be present on the computer. The Chromebook encrypts this data using tamper-resistant hardware, making it very difficult for anyone to access those files.
Há uma descrição muito detalhada do mecanismo de criptografia dos dados em cache aqui .