distsys-dec-6-2018.md

Blockchain - DistSys Lecture - Dec 6th, 2018

m = number of traitors n = number of nodes

n > 3m

Message Signing

Public Key & Private Key

encode(privatekey, message) -> ciphertext decode(publickey, cipherkey) -> v

send original message + signature(encrypted hash of message)

RSA Algorithm

Signed Messaging Algorithm

Decentralized Replicated Nodes

• No one point of failure

Blockchain

• A block is a set of transactions that happended during a window of time
• Every node has the history of every transaction that has ever happened in the blockchain
• Since this is a decentralized network, a malicious node can create malicious transactions — ex: transferring money that you don’t have haved
  • If a traitorous transcaction is sent out, honest nodes will ignore it
  • Honest nodes only accept valid transactions
• We want to artificially slow down the addition of blocks to the chain
  • Adding a block to the chain requires solving a mathematical problem that requires some computational power
  • This slows down the addition of blocks
  • At any time there are multiple nodes trying to solve the same problem to add a node

Math Problem

uninversible hash function hash(block + nonce) = 00000…..

51% Attack

What if we have supercomputers that can solve math problems faster that the loyal nodes?

• If you own more than 50% of the computing power in the blockchain network, then you can start inputting malicious blocks into the chain

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