Blockchain Exam 1

256 bits

RSA

True

A random number used only once (in a lifetime or in a communication session)

Symmetric key cryptography

Asymmetric key cryptography

Variable size input

All of them can be detected

Privacy

True

False

Double Spending

A binary tree with hash pointers that can verify membership in O(log n) time and when it is sorted you can also verify non-membership in O(log n) time.

sk: secret signing key pk: public verification key

Three algorithms (sk, pk) := generateKeys(keysize) sig := sign(sk, message) isValid := verify(pk, message, sig)

The first block created in the blockchain

-No single bottleneck -More reliable: fault tolerant -More secure: Attack tolerant -No single point of control: No monopoly

City Records, Banks, voting authorities, Networks

Barter system, it was peer-to-peer

Money is a broader term that refers to an intangible system of value that makes the exchange of goods and service possible, now and in the future. Currency is simply one, tangible form of money.

A set of ideas and practices which organize what we produce and consume, and the way we live together

Unit of Account: Defines Values Medium of Exchange: Acceptability Store/Transfer of Value: Non Perishable

Only sender, intended receiver should "understand" message contents -Sender encrypts message -Receiver decrypts message

Sender and receiver want to confirm of each other

Sender and receiver want to ensure message not altered (in transit, or afterwards) without detection

Services must be accessible and available to users

Interception of messages

Can fake (spoof) source address in packet (or any field in packet)

"Take over" ongoing connection by removing sender or receiver, inserting himself in place

Prevent service from being used by others (e.g., by overloading resources)

m: plaintext message K_A(m): Ciphertext, encrypted with key K_A m = K_B(K_A(m))

Key is shared by sender and receiver

Confidentiality from intruder/eavesdropper; only accessible by a legitimate receiver

-The input can be any string of any size -It produces a fixed-size output -Is efficiently computable -Is deterministic (same input produces same output)

Substituting one thing for another (e.g., monalphabetic cipher)

Sender and receiver do not share secret key. Public encryption key is known to all but the private decryption key is known only to receiver.

1. Choose two large prime numbers p and q

2. Compute n = pq, z = (p-1)(q-1)

3. Choose e (where e<n) that has no common factors with z (e,z are "relatively prime")

4. Choose d such that ed mod z = 1.

5. public key is (n,e) and private key is (n,d).

Property 1: Collision-Resistance Property 2: Hiding Property 3: "Puzzle Friendliness" (One-Way)

Nobody can find x and y such that x != y and H(x) = H(y)

Given H(x), it is infeasible to find x.

For every possible output value y, if k is chosen from a distribution with high min-entropy, then it is infeasible to find x such that H(k | x) = y.

Each block contains transactions to be validated and the previous hash value.

A release of data is said to have the k-anonymity property if the information for each person contained in the release cannot be distinguished from at least k-1 individuals whose information also appear in the release

A pointer to where some info is stored and the hash of the info

We can ask to get info back, and verify that it hasn't changed

-No centralized server (single point of failure, censorship) -Key Primitive (Broadcast blocks and transactions to all nodes) -Robustness over churns (Some nodes go offline, new nodes join)

-Its a Peer to peer network -Mining is open to anyone -There are updates to software by core developers trusted by the community

1. Join the network and listen for transactions

2. Listen for new blocks and maintain the block chain

3. Assemble a new valid block

4. Find the nonce to make your block valid

5. Hope everybody accepts your new block

6. Profit

-Easily available and easy to set up -Parallel alus -Bit-specific instructions -Can drive many GPUs from 1 CPU -Can be overclocked

The idea that some errors are okay

Goodput: throughput x success rate

Worth over-clocking by 50% with 30% errors

-Poor utilization of hardware -Poor cooling -Large power draw -Few boards to hold multiple GPUs

-Higher performance than GPUs -Better Cooling -Extensive customization and optimization

-Higher draw than GPUs designed for -Poor optimization of 32-bit adds -Fewer hobbyists with sufficient expertise -More expensive than GPUs -Marginal performance/cost advantage over GPUs

An application-specific integrated circuit for bitcoin mining. -Designed to be run constantly for life -Require significant expertise, long lead-times -Perhaps the fastest chip development ever

Energy used to manufacture mining chips & other equipment

Used to perform computation

Required to protect equipment

Pool participants all attempt to mine a block with the same coinbase recipient, send the money to the key owned by the pool manager, then distribute revenues to members based on how much work they have performed.

-Pay per share: flat reward per share, minus a significant fee -Proportional: Typically since last block, lower risk for pool manager, and more work to verify -"Luke-jr" approach: No management fee, miners can only get paid out in whole BTC, pool owner keeps spread

1. Address: hash of a public key

2. Transaction inputs and outputs

3. Signatures on transactions

4. UTXO model

5. Transaction Fees

6. Coinbase transactions

7. Transaction mempool

1. The block version

2. Previous block header hash

3. Merkle Root Hash

4. The block time

5. Difficulty Target

6. Nonce

Transactions or blocks may conflict, but the default behavior is to accept whatever is heard first. The network position matters

You relay a new block when you hear it if: the block meets the hash target and the block has all valid transactions

-Built for Bitcoin -Simple and compact -Support for cryptography -Stack-based -Limits on time and memory -No looping -Turing-incomplete