Cryptographic Protocols and Algorithms for 5G. Elena Dubrova School of Information and Communication Techonology, KTH

Transcription

1 Cryptographic Protocols and Algorithms for 5G Elena Dubrova School of Information and Communication Techonology, KTH

2 Overview PROTOCOLS ALGORITHMS IMPLEMENTATIONS OBJECTIVES TO IMPROVE ATTACK RESISTANCE OF 5G RADIO ACCESS NETWORKS TO IMPROVE EFFICIENCY OF CRYPTOGRAPHIC ALGORITHMS TO PROTECT HARDWARE FROM TAMPERING RESULTS RANDOM ACCESS PROCEDURE BASED ON TUNABLE PUZZLES ENERGY- EFFICIENT ENCRYPTION AND AUTHENTICATION ALGORITHMS METHODS FOR SECURE KEY STORAGE COUNTERMEASURES AGAINST HARDWARE TROJANS 2

3 Random- Access Procedure Based on Tunable Puzzles

4 Background: Computational Puzzles Developed for IP-based network protocols Delay access to server resources Cryptographic hash function F Solution requires ~2 p hash function computations Verification requires 1 hash function computation Client Request Puzzle p = F(s) Solve puzzle Solution s Grant Server 4

5 Our contributions 1. We have shown usability of puzzles for radio networks, as a means of balancing the load on base station [1] 2. We generalized puzzles to enable prioritization Access preambles are partitioned into two sub-sets 3. We introduced a way to encode auxiliary information into puzzle s solution without making puzzles harder to create Auxiliary information specifies on which radio resource the next message should be sent 5

6 Proposed Random Access Procedure Step 1: Access request according to device priority type Step 2: Response contains computational puzzle based on priority Step 3: Solution specifies radio resource to be used in subsequent signaling to the base station Device Request (priority i) Solve puzzle Puzzle p(i) [Radio resource determined by solution s(i)] Grant Base Station 6

7 Mitigation of false claims A malicious device may falsely claim to have priority by using a preamble from the set of prioritized preambles, P P However, in return it will receive a puzzle which cannot be solved without a key Malicious Device? Request (preamble in P P ) Puzzle p for prioritized devices If device doesn t have the key, it cannot solve the puzzle Base Station 7

8 Energy-Efficient Cryptographic Algorithms

9 Background: Cyclic Redundancy Check (CRC) n-bit CRC detects: all burst errors up to length n CRC does not withstand crafted error, only random An injection attack in which the injected error is a multiple of the CRC generator polynomial will not be detected PHY Layer HEADER BODY CRC LTE uses 24-bit CRC ZigBee uses 16-bit CRC 9

10 Cryptographic CRC Proposed by Krawczyk in 1994 [2] Uses irreducible generator polynomials which are selected pseudo-randomly and changed periodically Compared to other Message Authentication Codes (MACs): (+) Detects burst errors (+) Can be computed with less resources (+) Provably secure with a quantifiable failure probability ε (-) ε > 1/2 n (-) Requires irreducibility test 10

11 Drawbacks of existing methods Crypto-CRC of Krawczyk and other MACs used in wireless communication standards cannot correct errors If MAC verification fails, the message is discarded and a retransmission is requested Re-transmissions waste energy and increase average packet latency Excessive re-transmissions may lead to network congestion 11

12 Our contribution We introduced a MAC which efficiently combines integrity protection with single-bit error correction [3] (+) Preserves all advantages of Krawczyk s CRC (+) Does not require irreducibility test (-) ε our > ε Krawczyk Good candidate for simpler 5G radio types and use cases with constrained resources such as machinetype communications 12

13 Energy-efficient encryption We designed a stream cipher Espresso [4] Fastest among the ciphers below 3000 µm 2, including Grain-128 and Trivium (winners of ECRYPT competition) Area (µm 2 ) Throughput (bits/s) Energy per bit (pj) AES-ECB Espresso times smaller 9.5 times more energy efficient 13

14 Hardware Security

15 What will 5G bring? More not so well protected wirelessly connected devices will contain sensitive data or be involved in services related to sensitive data E-health Wearable devices Smart home Connected cars source: [5] 15

16 Side-channel attacks become cheaper The equipment to do side-channel attacks becomes cheaper continuously With a $2,000 piece of equipment one can extract practically any data from a chip if the chip is not hardened against side-channel attacks [6] 16

17 Is the sensitive data well protected? Sensitive data is typically stored in a non-volatile memory a volatile memory with a battery programmable fuses Various mechanisms are used to protect sensitive data from readback or tampering Anti-tamper switches, sensors, wire meshes,... source: uk.farnell.com source: [7] source: /12/02/lm75b-temperature-sensor/ source: /robust-hardware-security-devices-madepossible-laser-direct-structuring 17

18 Memory zeroization Erasing critical parts of memory in response to tampering is called zeroization However, zeroization mechanisms often require a continuous power supply an attacker can disable them before powering up a chip Another problem is data remanence residuals of data remain after erasure 18

19 Data remanence in volatile memories Contrary to conventional belief, volatile memories (SRAM, DRAM) do not entirely lose their contents when power is turned off [8] for SRAM, at room temperature the data retention time varies from 0.1 to 10 sec cooling SRAM to -20ºC increases the retention time to 1 sec to 17 min at -50ºC the retention time is 10 sec to 10 hours source: revision3.com 19

20 Data remanence in non-volatile memories It may take many cycles to erase data from a nonvolatile memory (EEPROM, Flash, etc.) Data was successfully recovered from the Flash memory PIC16F84 after 10 erase cycles [9] To overcome this problem, it is recommended to erase data by writing all-0, all-1, and random data in the memory source: [7] 20

21 Are security fuses secure? Security fuses can be set to protects on-chip memories from non-authorized access Modification or readback of sensitive regions of memory is prevented

22 Defeating security fuses Some security fuses can be reset with UV light [10] Metal shields over the security fuses can be surpassed by placing the chip at an angle To prevent the erasure of data from the Flash memory, a piece of electrical tape can be placed over the Flash With fuses disabled, the content of the Flash can be read out PIC 18F1320 microcontroller

23 Our countermeasures source: vt.edu/puf/main.html The attack presented in [10] can be mitigated using more secure methods for key storage, including Encode a key in a Finite State Machine (FSM) and implement the FSM on-chip by a sequential circuit [11] Store a key using a Physical Unclonable Function (PUF) [12] PUF is a silicon fingerprint unique for each chip due to random physical factors introduced during manufacturing 23

24 Anti-tamper measures may backfire 24

25 Becker s attack on Intel s RNG [15] (a) CMOS Inverter [15] (b) Trojan inverter with output = V DD [15] A hardware Trojan was implanted in Intel s RNG by modifying dopant masks of selected transistors to shorten their outputs to V SS or V DD Practically impossible to detect by visual inspection Modifications do not trigger Built- In Self Test (BIST) 25

26 Out countermeasure The attack presented in [15] can be mitigated by making BIST test patterns (and hence the expected signature) unknown at the manufacturing stage [16] BIST initial test pattern are made dependent on a key which is programmed into a chip after the manufacturing stage 26

27 Conclusions It is important to assure security at all levels: Protocols, algorithms, implementation Do not assume hardware to be trustworthy Instead, design your system to be tamper-resistant Training of security designers is important Countermeasures against one attack can backfire and enable other attacks 27

28 References [1] Dubrova, E., Näslund, M., Selander, G., Lindqvist, F., A Random Access Procedure Based on Tunable Puzzles, IEEE Conference on Communications and Network Security, 2015, pp , available at random-access-procedure.pdf [2] Krawczuk, H., LFSR-Based Hashing and Authentication, CRYPTO 94, pp [3] Dubrova, E., Näslund, M., Selander, G., Norrman, K., Error-Correcting Message Authentication for 5G, submitted to IEEE International Workshop on 5G Security, 2016 [4] Dubrova, E., Hell, M, Espresso: A Stream Cipher for 5G Wireless Communication Systems, Cryptography and Communications, available at [5] M. Ford, Lead Generation Tips Things You Do Not Tell Prospects, sales-management/lead-generation-tips-things-you-do-not-tellprospects #OMBu1jkkPAmByVsp. 99 [6] E. Worthman, ChaoLogix: Integrated Security, Semiconductor Engineering, 13 April 2015 [7] Physical Protection: Anti-Tamper Mechanisms in CC Security Evaluations, ALVARO_ORTEGA_EPOCHE&ESPRI_Physical_protection_Anti_tamper_mechanisms.pdf [8] S. Skorobogatov, Physical Attacks on Tamper Resistance: Progress and Lessons, Special Workshop on HW Assurance,

29 References, cont. [9] S. Skorobogatov, Data Remanence in Flash Memory Devices, CHES 2005 [10] Hacking the PIC18F1320, [11] N. Li, S. Mansouri, E. Dubrova, Secure Key Storage Using State Machines, Proceedings of ISMVL'2013, pp [12] S. Tao, E. Dubrova, An Ultra-Energy-Efficient Temperature-Stable Physical Unclonable Function in 65nm CMOS, Electronics Letters, 2016 [13] Joe Grand, Practical Secure Hardware Design for Embedded Systems, [14] O. Kömmerling, Design Principles for Tamper Resistant Smartcard Processors, Smartcard 99 [15] Becker, G., et al., Stealthy dopant-level hardware Trojans, Cryptographic Hardware and Embedded Systems (CHES 2013), LNCS 8086 pp , 2013 [16] E. Dubrova, M. Näslund, G. Carlsson, J. Fornehed, B. Smeets, Two Countermeasures Against Hardware Trojans Exploiting Non-Zero Aliasing Probability of BIST, Journal of Signal Processing Systems, 2016 [17] S. Skorobogatov, Fault Attacks on Secure Chips: From Glitch to Flash, ECRYPT II,