In this talk, the speaker will survey the security attacks on blockchain and compartmentalise attacks that are generic to IT systems, singling out real attacks specific to blockchain and their countermeasures.
10. Definition: Double-spending
> Double-spending problem
#ISSLearningFest
Double-spending is a potential flaw
in a digital cash scheme in which
the same single digital token can
be spent more than once. This is
possible because a digital token
consists of a digital file that can be
duplicated or falsified.
Source - https://en.bitcoinwiki.org/wiki/Double-spending
11. Definition: Double-spending
> Two Necessary Properties of Cryptocurrency
1. Unforgeability – achieved using digital signature
2. No double spending – achieved using blockchain (as public ledger,
anyone can see the spending)
#ISSLearningFest
13. Bitcoin utilizes blockchain to achieve no double
spending
#ISSLearningFest
Image - https://www.gemini.com/cryptopedia/what-is-bitcoin-
and-how-does-it-work#section-understanding-bitcoin
14. What is the block in blockchain: Bitcoin
transactions are grouped together into “blocks”
#ISSLearningFest
Image - https://www.gemini.com/cryptopedia/what-is-bitcoin-
and-how-does-it-work#section-understanding-bitcoin
16. What is the chain in blockchain: Each block is
chained onto previous block through hash function
#ISSLearningFest
Image - https://www.ig.com/en/trading-strategies/what-is-blockchain-
technology--200710
17. Cryptographic One-Way Hashing
Hash output is like a fingerprint in digital world
#ISSLearningFest
Image - https://www.freecodecamp.org/news/how-bitcoin-mining-really-works-
38563ec38c87/
19. Any node in public ledger can create the block
#ISSLearningFest
Image -
https://www.researchgate.net/publication/320127088_Blockchain_Implem
entation_Quality_Challenges_A_Literature_Review/figures?lo=1
20. The first miner to solve the math puzzle get to
create the block and receive bitcoin as reward
#ISSLearningFest
Image - https://forkast.news/proof-of-work-what-is-it-bitcoin-halving/
22. Blockchain Conflict
#ISSLearningFest
In scenario where 2 different miners solve the math puzzle at the same time,
and add their blocks to the last known block in the chain, would result in
blockchain conflict.
The two branches after Block 103 are valid. The next mined block may be
added in either of the branches.
Image - https://www.tutorialspoint.com/blockchain/blockchain_resolving_conflicts.htm
23. Resolving Blockchain Conflict
#ISSLearningFest
Suppose, the miner adds the newly mined block to Block 104-A, the branch
containing Block 104-A will be longer than the branch containing Block
104-B.
In Bitcoin architecture, the longest branch always wins, and the shorter ones
are purged. So Block 104-B has to be purged.
Image - https://www.tutorialspoint.com/blockchain/blockchain_resolving_conflicts.htm
24. How to double spend?
#ISSLearningFest
Alice has $10
Alice > Bob $10
Alice has $0
Alice has $10
Create a fake branch faster than
the authentic branch
33. Estimate: Cost of 51% attack on Bitcoin is USD
15 billion
#ISSLearningFest
https://www.bitpanda.com/academy/en/lessons/what-is-a-51-attack-and-how-is-
it-prevented/
34. Countermeasures 2: Truly Decentralized Network
#ISSLearningFest
“It’s almost impossible to pull that (51% attack) off in
established blockchains like Bitcoin and Ethereum.
This phenomenon has been experienced by some
small chains that are not really decentralized”
Avinash Shekhar, Co-CEO, ZebPay
Source - https://economictimes.indiatimes.com/markets/cryptocurrency/what-are-51-attacks-in-
cryptocurrencies/articleshow/85802504.cms?from=mdr
35. Global distribution of bitcoin nodes
#ISSLearningFest
Image - https://medium.datadriveninvestor.com/blockchain-getting-
started-what-is-bitcoin-full-node-40460f3acafa
36. Countermeasures 3:
ETC response on countermeasure
#ISSLearningFest
https://coingeek.com/ethereum-classic-rolls-out-51-attack-protection-plan/
37. Give Us Your Feedback
#ISSLearningFest
Day 1 Programme
