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Bitcoin PowerPoint Presentation


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  1. Bitcoin

  2. What is Bitcoin? • A P2P network for electronic payments • Benefits: • Low fees • No middlemen • No central authority • Can be anonymous • Each payment goes through, no censorship

  3. How Does it Work? • Does not rely on real currency but one can buy bitcoins for money • Valuable because they are useful and limited in supply • New coins are ”mined” by performing cryptographic operations that take lots of CPU • A user can package the new coin together with a block containing new transactions of others • “Verifying a block” brings the user 25 BTC reward • Reward is halved every 4 years

  4. How Does it Work? • Each transaction is signed by the sender’s private key • So no one can spend others’ money • Transaction = bitcoins, public key of recipient • Each transaction is broadcast in the P2P network • Recipients collect and verify transactions in a block • On the average 6 blocks per hour are generated

  5. How Does it Work? • Blocks are chained together so that latter blocks depend on previous ones • If multiple chains appear only the longest and fastest-growing chain is accepted as true • This prevents double-spending • Anonymity can be achieved by using a new public/private key pair for each receiving transaction

  6. Transaction Format

  7. Txin Format

  8. Txout Format

  9. Sample Transaction • Input 50 bitcoins from transaction with hash f5d… then send them to a Bitcoin address 4043 .. • If the input was greater than the amount you want to spend create another output to yourself with the rest • Any part of input not redeemed is the transaction fee and belongs to whoever generates a block

  10. Transaction Verification • Use a scripting system – describes how the transaction amount can be redeemed • Input’s scriptSig is evaluated first – this leaves some state on the stack • Output’s scriptPubKey is evaluated second • Through scripting system one can create different sorts of payments with different conditions

  11. Types of Transactions • Transfer to IP address • Transfer to Bitcoin address • Generation

  12. Blocks • A block is a record of some or all transactions that have not been recorded so far • Each block contains: • A reference to the block immediately before it – chaining (roughly one block is added each 10 min) • A solution to a cryptographic puzzle • A generation transaction so fee can be claimed for generating the block • Transactions are broadcast and peers compete in trying to generate new blocks • More about block rules

  13. Puzzles • A puzzle is finding an input to a hash algorithm that, when combined with the block’s hash results in output with many zeros • The difficulty of the puzzle is automatically adjusted so that roughly 6 puzzles per hour can be solved • Every two weeks all clients compare how much off target they were and adjust puzzle difficulty • Clients accept the chain with the highest combined difficulty of puzzles as valid

  14. Double-Spending • Could one spend the same coin twice? • Bitcoin peers verify all transactions they add to the block to ensure that the same coin wasn’t spent elsewhere • There are some race conditions that may lead to double-spending before transactions are verified • As the confirmations increase no double-spending is possible

  15. Some Statistics

  16. Some Statistics

  17. Some Statistics

  18. Some Statistics

  19. Some Statistics

  20. Some Statistics

  21. Some Statistics

  22. Drive-By Downloads

  23. What are Drive-By Downloads

  24. Are These Just Exploits? • If my computer is well-protected should I worry? • Drive-by downloads occur in two ways: • There’s a pop-up that a user clicks on or sometimes even closes. This is interpreted as permission to download and install malware onto your machine • There’s a script on the page a user visited that initiates file download. Some browsers may run such files automatically, infecting the machine • Some browsers will force downloads and warn on downloads of executable software

  25. What If I Visit Well-Known Sites? • Even such sites can have vulnerable servers that get infected by attackers • Or they may serve ads that distribute malware • Exploit kits for Web servers proliferate on black markets • They are also very versatile and customizable

  26. Are There Any Defenses? • Lots of research in the area from top security experts • BLADE“all executable files delivered through browser downloads must result from explicit user consent”