CMPSC 190N Blockchain

Characteristics of Bitcoin Script

stack-based, simple isntruction set, non-Turing complete, deterministic

Pay-to-Public-Key-Hash (P2PKH)

single signature spending requiring a private key

Multi-signature (Multisig)

Requires M out of N signatures for shared custody/governance

Pay-to-Script-Hash (P2SH)

Complex conditions through referencing a script hash

Zero-Knowledge proofs

verifies transaction without revealing underlying data

Proof of work

get reward through computing valid nonce value

Halving of block reward

Starting in 2008, starts at 50 btc, divides by half every 4 years. Currently at 3.125

Difficulty Adjustment Alg

every 2016 blocks (2 weeks at 10-minute intervals), maximum 4x change per adjustment

UTXO Model

stateless, new address for each transaction, high parallelization, limited scripting, simple 

Account Model

maintains account balances, reused addresses for transactions, limited parallelization, full programmability, complex

Externally Owned Accounts (EOAs)

controlled by private keys, initiates transactions, no code execution capabilities, used by human users and wallets, has nonce and balance

Contract Accounts

controlled by smart contract code, cannot initiate transactions, only responds to calls, contains executable bytecodes, has storage for persistent data

Nonce

for EOA, transaction counter preventing replay attacks

for contracts, number of contracts created

Balance

amount of Ether (in wei) owned by account, contracts can hold Ether

CodeHash

hash of the account’s code, points to executable bytecode, only for contracts

StorageRoot

root hash of the account’s storage trie, contains persistent data for smart contracts

Transfer Ether

sends ETH from one account to another

Call Contract Functions

executes code in existing smart contracts

Deploy Contracts

create new smart contracts on the network

to (transaction field)

Destination address or recipient

value (transaction field)

amount of ether to transfer

data (transaction field)

contract bytecode or function call data

gasLimit (transaction field)

maximum gas willing to spend

maxFeePerGas (transaction field)

maximum total fee per gas unit

maxPriorityFeePerGas (transaction field)

tip to minors for priority inclusion

Simple Transfer

to: recipient address

value: ETH amount

data: empty

Contract Call

to: contract address

value: ETH (optional)

data: function call

Contract Deployment

to: empty (null)

value: ETH (optional)

data: bytecode

Upfront payment of gas

gasLimit * maxFeePerGas

Common gas costs

basic operations (add, mul, etc.): 3-5 gas

memory operations: 3-200 gas

storage write: 20000 gas

contract creation: 32000 gas

Total Fee

GasUsed * (BaseFee + PriorityFee)

Base Fee

burned by admin to reduce ETH supply and prevent inflation

Priority Fee (Tip)

user-set tip to incentivize minors/validators to include the transaction quickly

Stack

LIFO with maximum of 1024 items, each item is max 256-bits

Memory

temporary byte-addressed storage that expands dynamically during execution, cleared after each call completes

Calldata

read-only input bytes passed to contract during transaction or call, contains function identifiers and encoded parameters, must be loaded onto stack for processing

Storage

persistent key value map from 256 bit keys to 256 bit values, survives after the call finishes, all slots initially zero

PUSH(1-16)

adds value to ith spot

DUP(1-16)

duplicates ith value to top

SWAP(1-16)

swaps top value with ith value after it

POP

removes top item

Arithmetic OPcodes (add, sub, mul, div, mod, addmod, mulmod)

256-bit modular arithmetic operations wraps at 2^256 on top two values of stack

Comparison opcodes (LT, GT, EQ, ISZERO)

compares top two values and produces boolean results

Control Flow OPcodes (JUMP, JUMPI, JUMPDEST, REVERT, STOP)

implements conditional and unconditional branching, JUMPDEST marks valid targets

Return OPcodes (RETURN, REVERT)

halts execution and return data (RETURN) or revert state changes (REVERT)

memory, storage, calldata opcodes (mload, mstore, mstore8, sload, sstore, calldataload, calldatasize, calldatacopy)

read and writes to top of stack, store expects key at top, value at 2nd, copy expects destoffset, offset, length

PUSH, DUP, SWAP cost

3 gas

POP cost

2 gas

ADD, SUB, MUL cost

3-5 gas

DIV, MOD cost

5 gas

LT, GT, EQ cost

3 gas

MLOAD, MSTORE cost

3 gas + expansion

SLOAD (warm) cost

100 gas

SLOAD (cold) cost

2100 gas

SSTORE (warm) cost

2900 gas

SSTORE (cold, new) cost

22100 gas

JUMP, JUMPI cost

8 gas

CALL cost

100+ gas (base)

Cold Access

first time accessing a storage slot in a transaction, first time calling a contract address, very high costs, compensates for loading data from disk

Warm Access

subsequent access to same slot/address, data already cached in memory, lower gas costs (than cold access), rewards batching operations

Read Batching

batch multiple reads from the same storage slot to reduce gas cost by turning cold reads into warm reads

Write Batching

accumulate changes in memory, commit once to storage, minimizes number of SSTORE operations

Cold to warm cost ratio

7.6x