Unicorn: Two- Factor Attestation for Data Security

Transcription

1 ACM CCS - Oct. 18, 2011 Unicorn: Two- Factor Attestation for Data Security M. Mannan Concordia University, Canada B. Kim, A. Ganjali & D. Lie University of Toronto, Canada 1

2 Unicorn target systems q High value data q overkill for casual Facebook profile q Requires: q hardware support q PSD: personal security device q custom application package 2

3 Goal malware q Protect entire user session q Not limited to login & other credentials 3

4 Goal phishing q Protect Unicorn credentials q Less reliance on user diligence during authentication wwwbank.com 4

5 Goal automatic security q Unicorn: access to data depends on system state q Ideal: functionality tied to system health avoids the unmotivated user problem 5

6 Dealing with Phishing q Use security token q generate one time passwords or do challenge response q adversary must steal/clone a token q or: hack RSA J But no protection against malware! 6

7 Dealing with malware q Use trusted computing hardware to verify the integrity of a computer (TPM, Intel TXT, AMD SVM) q compute hashes of BIOS, boot loader, OS, q sign hashes to prove that computer is not running unwanted code Notifying the current system state to users isn t easy [Libonati, NDSS 2011] 7

8 Combine the two? q Unicorn: security token + trusted computing q Unicorn applications are called uapps q uapp: small OS + one application q User OS: open, uapps: closed 8

9 Unicorn design q Token is used to verify attestations q only releases authentication credentials if system is malware free q verifies: system memory + disk image q Attacker must q clone or steal the token q physical access to user s computer q assumption: no vulnerabilities in Unicorn 9

10 Unicorn example setup q Security tokens currently not capable of attestation q smartphone as PSD AIK PCRs, Auth User diligence is needed 10

11 Unicorn example steps Verify 11

12 Starting a uapp q Suspend, save user OS state q option 1: reboot into uapp q option 2: use DRTM q User OS as the bootloader q Resume: q direct transfer back to user OS Save state Hardware Reset BIOS Boot loader uapp OS 12

13 uapp usage scenarios q Two example cases q data stored on a remote server q data stored encrypted on local machine q Token is initialized with a secret key q remote server case: signing/mac key q local machine: encryption sub- key 13

14 Remote server case (MAC key) (TPM keys) Nonce, PCRs Quote(Nonce, PCRs) MAC(Quote(Nonce, PCRs)) 14

15 Local machine case q Encryption key consists of two subkeys: q subkey 1: on smartphone q subkey 2: sealed into computer s TPM Nonce, PCRs Quote(Nonce, PCRs) Subkey 15

16 Unicorn prototype q Extensions to Linux kernel q one line change in user OS kernel q Transfer directly to uapp OS via kexec q q loads uapp kernel image into memory saves state & transfer control to uapp loader q uapp loader based on tboot package q q q sets up a measured launch environment (MLE) measures the loaded kernel kernel measures the disk image during boot 16

17 uapp images q uapp image should be small q smaller attack surface & faster verification q we use a small Linux distro with a space efficient file system (squashfs) q uapp is network restricted q communicate only with remote server q help against TPM relaying attacks q SSL cert: only one trusted CA 17

18 TPM relaying q Attacker relays attestation requests to legitimate machine q but legitimate uapp will only communicate with remote server x x 18

19 Switching between commodity OS & uapp q Majority of cost: suspending the user OS and kernel boot q uapp loader is slow because TPM is slow Task Time (seconds) Suspend of user OS uapp Loader 3.29 Kernel boot and Xserver startup 7.20 OS hash 3.85 Unicorn Total Switching via reboot

20 Conclusion q Unicorn for two- factor data protection q q q physical access to user PC & compromised token for users: no passwords to remember or judge the safety of their computing environment switching: skip hardware reset and BIOS q ~45% reduction in switching time vs. previous methods q Enable automatic security 20

21 Questions, comments Thank you! 21