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72 lines
2.4 KiB
Markdown
72 lines
2.4 KiB
Markdown
---
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title: "412-lectures"
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aliases:
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tags:
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---
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# Lecture 7
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copmuter security
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- physical
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- software (authenticity correctness)
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- information (CIA/ IAS octave)
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- network
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cryptography can be bad because
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- you are still giving access to data in some form
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- how long will the cipher remain secure
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- managing keys can be challenging
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crypto in CIA
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- c - hide information
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- i - check for changes, checksums, MACs, Digital signatures
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- a - not directly, but indirectly, validate authentity of network link usage
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fallible machines
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- ram corruption, fade or malfunction of storage media, software issues (fs bugs, compression bugs, etc)
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- solution
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- estimate probability of failures, determine how many trials to achieve a certain level of confidence
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- aside: mahcines are designed to fail frequently
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- reliability tradeoff with increases in speed/power consuption (e.g., overclocking)
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distributed consensus
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- e.g., Master/master relational database
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- NoSQL gossip protocols, and eventual consistency
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- network instrastructure e.g., routers as hot spares
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- consensus gathering systems
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- apache zookeeper distributed synchronisation
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- etcd (used in kubernetes)
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dist cons algorithms
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- fischer lynch paterson impossibility result
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- paxos - fault tolerant consensus over distributed nodes (use din apache zoo)
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- raft - alternative to paxos used in etcd
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- easier than paxos to understand and implement
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- sub problems: leader election, log (data) replication by leader to followers
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- EPaxos - more compex and efficient that paxos
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all used when all servers are trusted. when there are malicious parties the consensus set size must grow. you need a majority of votes from the asumed-benign server set.
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permissionless blockchain - do not control the server set, safety presumed if 50% of nodes are benign
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fault tolerance
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- CFT - when a node dissapears
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- BFT - nodes acting maliciously
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- raft and paxos only CFT, variants of Paxos are BFT
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building a cryptocurrency
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- how to make a 'coin'
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- how to id coin owners
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- how to protect from forgery
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- how to record ownership and transfer of ownership
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- how are coins single-use
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distributed consensus in bitcoin
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- track who has what (in normal currency done by banks)
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- bitcion has all validating nodes store the whole ledger - indicates order of transactions
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- collectively agreeing its content avoid double spending
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- a wallet is a hash of a public key a client generates
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proof of work
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