Mobiflage deniable encryption for mobile devices

Structure of Presentation

MotivationOverviewIntroductionImplementation compromisesLimitationsConclusion

Structure of Presentation

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Motivation

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Overview

Syrian refugee risked his life to smuggle his phone’s micro SD card, containing evidence of atrocities, across international borders by stitching the card beneath his skin.

http://www.thestar.com/news/world/article/1145824

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What is plausible deniable encryption (pde)?& Why do We need it??

Deniable encryption algorithms have been devised to hide the very existence of encrypted data.

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File based encryption

Selected individual files are encrypted with unique keys

Keys are wiped from RAM when device is screen locked

BlackBerry and Apple iOS

System/Full Disk Encryption (FDE)

Block ciphers act on individual disk sectors Files only exist in a decrypted state while they are in RAM Pre-boot authenticator to unlock/mount disk Key stays in RAM while screen locked (for background IO) Google Android and Microsoft Windows Phone

Background on mobile storage encryption

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Plausible deniable encryption (PDE)

Level of protection beyond semantic security

Tools such as TrueCrypt provide PDE for desktop/laptop PCs

Different reasonable plaintexts may be output from a given ciphertext, when decrypted under different decoy keys.

PDE is arguably more important for mobile devices

Background on mobile storage encryption

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Mobiflage is a steganographic (data hiding) technique.

Mobiflage enables PDE on mobile devices by hiding encrypted volumes within random data in a device's free storage space.

Mobiflage scheme was designed and implemented for the Android OS.

Counter measures for threats specific to mobile systems and known attacks against desktop PDE implementations are incorporated into the design

Mobiflage

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Android 4.x has two partitions that store data. Ext4 Internal partition Store userdata (Apps ,Settings etc..) Meta data located anywhere on the disk FAT32

External partition. Stores documents, downloads, photos, etc. All meta-data at beginning of volume

File-system Support

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Implementation

We implement mobiflage by hiding data in the external storage of the device

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User boots into a given mode based on the supplied passwordStandard Mode Encryption without deniability For day-to-day use of mobile device Mounts outer volumes PDE Mode Encryption with deniability Used only when the user needs to gather/store hidden data Mounts hidden volume

Apps and data in each mode are independent ,essentially two isolated installations are present

Mobiflage Modes

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H - hash function vlen -number of 512-byte sectors on the storage device pwd - true password salt -random value for Hash function The generated off set is greater than one half and less than three quarters of the disk

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Leakage from File-system

Leakage from software

Password guessing

Storage snapshots

Sources of compromise addressed by Mobiflage

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Mismatch between device logs and carrier/web service logs

Some defenses include: Disable cell antenna Use anonymous SIM Use public WiFi Use pseudonymous accounts

Collusion with carriers

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Currently requires removable SD card or internal FAT32 partition

User cannot choose size of hidden volumes

Only 50% of SD card can be used safely

Currently, we support only one hidden volume offset

No clean solution to transfer data between modes

Limitations

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Mobiflage hides encrypted volumes in external storage incurring a tolerable impact on performance

Requires conscientious users to maintain deniability

Mobiflage will be more useful to regular users and human rights activists

Conclusion

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[1] International Journal of Emerging Technology and Innovative Engineering Volume I, Issue 4, April 2015

[2] Mobiflage: Deniable Storage Encryption for Mobile Devices by Adam Skillen and Mohammad Mannan[IEEE TRANSACTIONS ON DEPENDABLE AND SECURE COMPUTINGVOL. 11, NO. 3, MAY-JUNE

2014]

[3] Deniable Storage Encryption for Mobile Devices by Adam Skillen [A Thesis in the Concordia Institute for Information Systems Engineering April 2013] [4] On Implementing Deniable Storage Encryption for Mobile Devices by Adam Skillen and Mohammad Mannan

Reference

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