This document discusses blockchain and bitcoin. It provides information on hash functions and their security properties used in blockchain. It explains what blockchain is and how bitcoin works as a decentralized digital currency. Some key details on bitcoin include its creation in 2008, average price of $300, and challenges around creation of virtual currency and preventing double spending. The document also discusses security aspects of bitcoin like authentication through public key cryptography and digital signatures, integrity through cryptographic hashing, and availability through broadcasting on the peer-to-peer network. It provides tips on securely storing bitcoin private keys and wallets. Finally, it mentions that bitcoin is not authorized in Bangladesh due to money laundering and terrorist financing regulations.

1. Group Member
Md Habibur Rahman 152-15-6040
Md Juwell Musa 152-15-5682
Akteruzzaman 152-15-5671
S.m.Zahidul islam 152-15-5925
Presented By

2. BLOCKCHAIN
Hash Function :
• Take any string as a input
• Fixed size output (256 bit)
• Efficiently computable
Security Properties :
• Collision free
• Hiding
• Puzzle friendly

3. BLOCKCHAIN
Data Data Data Data
Prev: H() Prev: H() Prev: H() Prev: H()
H()
o What is BLOCKCHAIN ?

4. Bitcoin
• A distributed, decentralized digital currency system
• Released by Satoshi Nakamoto 2008
• Effectively a bank run by an ad hoc network
• Digital checks
• A distributed transaction log

5. Size of the BitCoin Economy
• Number of BitCoins in circulation 11.8 million (December 2013)
• Total number of BitCoins generated cannot exceed 21 million
• Average price of a Bitcoin: around $300
 Price has been unstable.
• Total balances held in BTC 1B$ compared with 1,200B$ circulating in
USD.
• 30 Transactions per min. (Visa transaction 200,000 per minute.)

6. BitCoin: Challenges
• Creation of a virtual coin/note
• How is it created in the first place?
• How do you prevent inflation? (What prevents anyone from creating lots of coins?)
• Validation
• Is the coin legit? (proof-of-work)
• How do you prevent a coin from double-spending?
• Buyer and Seller protection in online transactions
• Buyer pays, but the seller doesn’t deliver
• Seller delivers, buyer pays, but the buyer makes a claim.
• Trust on third-parties
• Rely on proof instead of trust
• Verifiable by everyone
• No central bank or clearing house

7. Security in BitCoin
• Authentication  Public Key Crypto: Digital Signatures
• Am I paying the right person? Not some other impersonator?
• Integrity  Digital Signatures and Cryptographic Hash
• Is the coin double-spent?
• Can an attacker reverse or change transactions?
• Availability Broadcast messages to the P2P network
• Can I make a transaction anytime I want?
• Confidentiality Pseudonymity
• Are my transactions private? Anonymous?

8. How Can I Secure My BitCon?
• Do Not Use Web Wallets
• Separate your Bitcoins to Hot and Cold Wallets
• Store Private Keys Offline
• Use a Dedicated Hardware
• Use Linux on Online and Offline Computers
• Keep a Highly Secure Offsite Backup
• Make Use of a Type 2 Deterministic Wallet

9. Public Key Crypto: Encryption
• Key pair: public key and private key

10. Public Key Crypto: Digital Signature
• First, create a message digest using a cryptographic hash
• Then, encrypt the message digest with your private key
Authentication
Integrity
Non-repudiation

11. 11
Cryptographic Hash Functions
•Consistent: hash(X) always yields same
result
•One-way: given Y, hard to find X s.t. hash(X) =
Y
•Collision resistant: given hash(W) = Z, hard
to find X such that hash(X) = Z
Hash FnMessage of arbitrary length
Fixed Size
Hash

12. Why not in Bangladesh?
• Bitcoin is not an authorized
• Violation of the existing money laundering and
terrorist financing regulations
• financial loss of the citizens

13. References :
University : Princeton (USA)
Week : First week second lecture
Taught by: Arvind Narayanan, Assistant Professor(Computer Science)
Link : https://www.coursera.org/learn/cryptocurrency/home/welcome
Type : Research paper
Publisher : Emerald Publishing Limited
Accepted : 27 September 2017
Author(s) : Zhi Li, (Guangdong Provincial Key Laboratory of Computer Integrated
Manufacturing Systems, School of Electromechanical Engineering, Guangdong
University of Technology, Guangzhou, China)
Link : http://www.emeraldinsight.com/doi/abs/10.1108/IMDS-04-2017-0142