Sichere Datenspeicherung in der Cloud

Verschlüsselung in der Cloud – selbst gemacht

Thomas Lorünser

AIT Austrian Institute of Technology GmbH

Linuxwochen 2015

What is the cloud?

The NIST Definition of Cloud Computing

Special Publication 800-145

* Essential characteristics of cloud computing
* Different Service models
* Different deployment models

Essential characteristics of cloud computing

* On-demand self-service
* Broad network access
* Resource pooling
* Rapid elasticity
* Measured services

Service models

* Software as a Service (SaaS)
* Platform as a Service (PaaS)
* Infrastructure as a Service (IaaS)

Deployment models

* Private cloud
* Community cloud
* Public cloud
* Hybrid cloud

Public cloud service are everywhere

* Dropbox
* Apple with iCloud
* Amazon AWS
* Google
* Microsoft
* Facebook?

Security threats

The Notorious Nine - Cloud Computing Top Threats in 2013

Cloud Security Alliance

1. Data Breaches
2. Data Loss
3. Account Hijacking
4. Insecure APIs
5. Denial of Service

6. Malicious Insiders
7. Abuse of Cloud Services
8. Insufficient Due Diligence
9. Shared Technology Issues

What about the provider?

The public cloud and free services?

What are the basic incentives of free services?

What is the product?

Who pays for it?

Your are the product!

* Your personal data are valuable!
* Your personal data is sensitive data!

Why are people giving their data away?

* Mail
* Contacts
* Pictures
* Location
* ...

Advantages of the public cloud

* Ubiquitous access is very convenient
* No need for an own infrastructure
* More secure for private people?

But, do we have to give up all privacy for that? => A bug in the trust model!

My idea of a secure cloud storage

Provider cannot access the data!

* Data must be encrypted
* Provider has no access to the key.

=> Zero-knowledge provider

Zero-knowledge provider

* Wuala
* Spideroak
* Tresorit
* Mega
* Sync.com
* TeamDrive

* Boxcryptor
* Viivo
* Cloudfogger

The case of Safemonk

* Proprietary solution
* Depency on external services
* Potential data loss

Can we make our own solution?

* Protect integrity and confidentiality of data
* Accessible from different devices
* Without own infrastructure
* Share data with teams and friends
* Security is end-to-end

Cryptography as major ingredient

* Symmetric cryptography as basic tool
* Encrypt data before they are transferred
* Use cryptographic file systems

What Cloud interfaces to use

Simple Storage Service

* Object based storage interface
* AWS de-facto industry standard
* Linux drivers and fuse mount tools exists

Proprietary interfaces

* Free services have own tools
* Come with full blown GUI interfaces
* Linux versions available for most services

Use filesystem level encryption

Advantages

* Flexible file-based key management
* Individual management of encrypted files
* Access control through the use of public-key cryptography
* Cryptographic keys only held in memory while file is open

Use filesystem level encryption

Disadvantages

* File names, file sizes, modification timestamps
* Number of files leaks
* Directory structures leak
* Write and access patterns

1. Approach - ownCloud

ownCloud - Pro/Contra

Advantages

* Self-hosted plus encrypted
* Rich functionality
* Privacy-proxy

Disadvantages

* Maintaining own infrastructure
* Stability
* Limited functionality

2. Approach - EncFs

EncFs - Pro/Contra

Advantages

* Easy to use
* Wide platform interoperability
* Compatible with lower layer changes

Disadvantages

* Security and privacy from file level encryption
* SECURITY of implementation!!!

EncFs - Clients

Desktop

* Linux commandline (enfs package)
* Linux GUI: Cryptkeepter, GNOME Encfs Manger
* Windows: encfs4win
* MacOS tools

Mobile

* Cryptonite
* BOXCRYPTOR Classic

Web based

* EncfsAnywhere

EncFs - Security

EncFS is probably safe as long as the adversary only gets one copy of the ciphertext and nothing more. EncFS is not safe if the adversary has the opportunity to see two or more snapshots of the ciphertext at different times. EncFS attempts to protect files from malicious modification, but there are serious problems with this feature.

EncFs - Problem

(in older versions, problems are partially fixed now; version 2.x will be even better)

3. Approach - eCryptfs

eCryptfs - Pro/Contra

Advantages

* Good security
* Maintained by large community
* Good level of maturity

Disadvantages

* Not so easy to use
* Only for Linux (kernel level implementation)
* Problems with network mounts
* Problems with lower level syncs (cache)