Side channel analysisPractice and a bit of theory

Ilya Kizhvatov

2

About myself

• Senior security analyst at Riscure, Delft

• PhD, University of Luxembourg

• Diploma in IT security, ФЗИ РГГУ, Moscow

3

Side channel analysis in 3 minutes

4http://insidenanabreadshead.com/

5

6

Simple power analysis

https://www.icmag.com/ic/showthread.php?t=217895

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Countermeasure

Cost-effective: saves 150M euro yearly in NL

http://www.deweblogvanhelmond.nl

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Differential power analysis

+ + +…

substation

households

–

∆ ≠ 0?

9

10

In the remaining 45 minutes:Side channel attacks

on embedded devices

• When and where are they applicable?

• How they work?

• What complicates them?

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Embedded devices

A.78%B. 92%C. 98%

1. G. Borriello and R. Want. Embedded Computation meets the World Wide Web. Commun. ACM, May 2000

Absolute numbers for 2015: 15 billion connected devices2

7 billion people in the world1

How many out of all computing devices are embedded?

2. John Gantz. The Embedded Internet: Methodology and Findings. IDC, January 2009

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Examples with secure context

code execution

keys

PayTV

Smart grid

Mobile paymenthttp://en.wikipedia.org/wiki/File:Mobile_payment_01.jpg

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How to protect keys?

Pure software(whitebox crypto)

Go hardware

Recent overview: Dmitry Khovratovich @ 30C3

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When SW exploitation is not enough

flash

DDR

CPU secure core (crypto)

secure storage(keys)

internal ROM

password protection / lock

JTAG, I2C, …

encryption

Ethernet, USB, UART

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Secure boot

ROM loader code in flash

public keysignature

verify signature

Fault injection to skip. But when exactly?

20 Ways to Bypass Secure Boot: Job de Haas @ HITB KL 2013

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Power analysis of secure boot

Boot with valid flash image

Boot with invalid flash image

time to glitch

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Other examples

• Side Channel Analysis Reverse Engineering

• Interpretation of SW fuzzing effects

• JTAG password check (or PIN verification)

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Key recovery with SCA

Part 1: Basics

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A simple measurement setup

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21

Zoom-in

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Experiment: Look-up table

mov ZH, high(S<<1)mov ZL, R0lpm R0, Z

.ORG $800S:.db $63,$7c,$77,…

𝑆𝑎 𝑆 (𝑎)

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Hamming weight leakage of S(a)

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AES-128

𝑆𝑎 𝑆 (𝑎⨁𝑘)

𝑘

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Step 1: Acquire power traces

𝑎1𝑎2

𝑎𝑁

random input bytes

…

1

2

3

…

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Step 2: Predict leakage of guesses for

𝑎1𝑎2

𝑎𝑁

…

0 1 255

…

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Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

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Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

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Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

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Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

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Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

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Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

33

Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

34

Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

35

Step 3: Distinguish the right guess

𝑎1

𝑎2

𝑎𝑁

0 1 255

1

2

3

……

correlation

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Key recovery with SCA

Part 2: Complications

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Choice of side channel

http://www.dailymail.co.uk/news/article-2606972

39http://www.dailymail.co.uk/news/article-2606972

40http://news.bbc.co.uk/2/hi/uk_news/england/leicestershire/8447110.stm

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EM leakage: where to measure?

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EM leakage: where to measure?

Spectral intensityaround 32 MHz

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EM leakage: where to measure?

Spectral intensityaround 64 MHz

Distance betweenright and wrong

key guesses

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How to trigger?

• If dedicated trigger pin: easy

• Else if there is a pattern:– align online (special FPGA solution for triggering

on a pattern)– or align offline (processing complexity)

• Else attack as is (more traces needed)

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Misalignment: Spot a pattern

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Effect of misalignment on DPA

well aligned traces misaligned traces

Leakage spread across k samples k2 times more traces

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Which target variable?

• SW AES (ATmega)S-box output

• Simple HW AES (ATXmega, 8-bit datapath)S-boxi in XOR S-boxi+1 in

• Full-blown HW AES (128-bit datapath)staten-1 XOR staten (requires known inputs!)

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Which leakage model?

• Hamming weight (distance) often works

• More precise model faster attack

• Tools for leakage modelling:– Template attacks (profiling)– Linear regression

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Fitting a leakage model

{𝟏𝟔𝟒=𝜷𝒄𝒐𝒏𝒔𝒕+𝜷𝟎 ∙𝟎𝟏𝟓𝟎=𝜷𝒄𝒐𝒏𝒔𝒕+𝜷𝟎 ∙𝟏

…𝟏𝟖𝟎=𝜷𝒄𝒐𝒏𝒔𝒕+𝜷𝟎 ∙𝟏

measured leakage

target variable

predictions

Solution using OLS:

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Effect of a precise leakage model

Hamming weight model Model fit usinglinear regression

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How to brute force DPA output?

… … … …

x x x x x.0065

.0063

.0062

.0010

…

.0071

.0068

.0067

.009

.0069

.0068

.0067

.0010

.0068

.0067

.0066

.0011

.0072

.0069

.0066

.0013

.0070

.0068

.0065

.008

x…

𝑘1 𝑘2 𝑘16𝑘3 𝑘4 𝑘15

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How to brute force DPA output?

… … … …

x x x x x.0065

.0063

.0062

.0010

…

.0071

.0068

.0067

.009

.0069

.0068

.0067

.0010

.0068

.0067

.0066

.0011

.0072

.0069

.0066

.0013

.0070

.0068

.0065

.008

x…

• 5-6 candidates per byte full keys (1 day on a desktop PC)

• Solution: key enumeration (e.g. Veyrat-Charvillon et al. @ SAC2012)

• Challenge: memory consumption and therefore speed keys needs 70 GB of RAM and 9 days on a desktop PC

𝑘1 𝑘2 𝑘16𝑘3 𝑘4 𝑘15

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Countermeasures

• desynchronize• shuffle with dummy crypto operations

• masking (split sensitive variables into many)

• limit the number of crypto operationssmartcards: 65K operations only

• frequent key update

Most patented by CRI

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What makes an attack?

• Factors (according to JHAS*):– Time– Expertise– Equipment– Knowledge about the target– Number of device samples– Samples with known or chosen keys

• Identification ≠ exploitation* Joint Interpretation Library Hardware Attacks Subgroup

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Complexity indicators

Identification Exploitation

General-purpose microcontroller < day < hour

(< thousand traces)

SoC without SCAcountermeasures < month < week

(millions of traces)

SoC with SCAcountermeasures

> month+ advanced SCA skills

+ high-end DSO> month

(billions of traces)

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Special thanks to my colleagues at RiscureJob de Haas, Jing Pan, Eloi Sanfèlix, Albert Spruit

Contact: ilya@riscure.com