Team Wolf

Distributed, Consistent and

Secure USB StorageComprehensive Design Review

Eddie LaiMatt DubeSean BuschZhou Zheng

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Backing Up Data Everyone needs to save their work and data

• This data needs to be available in multiple locations• Data needs to be readily available• Today’s most popular storage device is the thumb drive

Backups have problems• Can be physically broken• Need to be carried around• Can wear out after a number of reads/writes

This leads to using multiple backups Multiple backups create problems

• Data changes create inconsistencies between backups• When many backups are created, data becomes vulnerable

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Distributed Consistent Secure USB Hub Our project: Distributed Consistent Secure USB Hub Makes maintaining backups simple and intuitive

• Uses off-the-shelf USB sticks for storage• Looks like a mass storage device to user’s PC• Can be accessed easily without any software installation

Maintains consistency• Storage Devices at different locations get updated

simultaneously• Synchronization as easy as a push of a button

Optional security measures• Secret sharing prevents users’ data from being compromised

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Outline Project Summary System Design

• PC Interface• File Consistency Software• Hub Communication• User Interface• Secret Sharing Software

Prototype Demonstration Question and Answer

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Step 1: User writes file to local USB hub Step 2: USB hub stores file on local USB sticks Step 3: User initiates a sync request Step 4: Consistency software detects file system updates Step 5: Hub distributes file system updates

Project Summary

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Project Design Implementation Parts implemented by team

• Consistency Software• Network Interface• PC interface• User interface

Additional ports and

processing provided

by embedded PC

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PC Interface Hub connects to PC without any software installation

• Not all users will be allowed to install software on their PC

Hub appears as a USB mass storage device Use USB OTG port

• By interfacing with the PC via this port, board appears as USB device• Shows contents of attached USB drives

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File Consistency Software Custom software to recognize when updates are made Changes recognized using conventional UNIX tools

• Timestamps and checksums recorded, then “diff”ed with previous record

What happens if a file is added?• Software recognizes timestamp and checksum change• Distributes file upon synchronization

What happens if only a timestamp is changed?• Software recognizes only a timestamp change• Distributes timestamp change, but does not re-distribute file

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Hub Communication TCP Client/Server Model

• Secure using SSL

Upon synchronization, the hubs will distribute updates across the network• When a hub is distributing updates, it will act as a client• The receiving hub will act as the server

Each client will connect to a server, distribute its updates, then disconnect

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User Interface Hub is manually operated by user Simple user interface consists of two buttons

• One button initiates synchronization• One button ejects USB sticks

Buttons are mounted on Hub via embedded PC’s GPIO ports Two LEDs provide feedback for users

• One alerts user when a sync is in progress• The other shows when it is safe to remove USBs from hub

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Secret Sharing User has option to share information secretly with other hubs If a USB drive is lost or compromised, no useful information

about its contents can be recovered (k,n) Threshold scheme

• Requires a subset, k, of a set, n, to recover data• With fewer than k pieces, no information about the

data can be recovered

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Secret Sharing Implements what is known as Shamir's[1] method for secret sharing

in the Galois Field 28

Method relies on the creation of a random polynomial• Samples various coordinates along the curve of the polynomial• Interpolates these points in order to reconstruct the secret

Functionality partially provided by libgfshare UNIX library

[1] Shamir, Adi (1979), "How to share a secret", Communications

of the ACM 22 (11): 612–613, doi:10.1145/359168.359176.

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Prototype Our Hub is currently being prototyped on an Advantech

development board powered by the Intel Atom The next prototype will be built on the BeagleBoard-xM

• Board offers a slimmer form factor − Lacks unneeded ports that Advantech board has− Solid state memory vs. HDD

• Primary motivation for using BeagleBoard is its USB OTG port− Allows the board to be mounted on User’s PC as USB mass storage device

Approx. cost with peripherals: ~$150

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Project Summary Distributed Consistent Secure USB Hub allows user to keep

backups on multiple USB sticks consistent Hub simplifies process for user

• Hub appears as USB mass storage device• Doesn’t require software installation on user’s PC• Simple user interface allows hub to be operated with only two buttons

Hub distributes updates to backups securely across network User has optional secret sharing functionality Prototype built using BeagleBoard-xM

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Demonstration Non Secret Sharing

• Scenario 1: Hub1 adds multiple files• Scenario 2: Hub2 removes file

Secret Sharing• Scenario 1: Hub1 adds multiple files• Scenario 2: Hub1 recreates a secret with all n shares present• Scenario 3: Hub2 recreates a secret with n-1 shares present

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Questions