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simple cryptography tools in blockchain

admin 11月 12, 2020 0

Hash Function

takes any string as input
fixed-sized output(usually 256 bits)
efficiently computable

security properties:

collision-free
hiding
puzzle-friendly

SHA-256

Hash Pointer

Merkle Tree

Digital signature scheme

Only you can sign, but anyone can verify

(sk, pk) := generateKeys(keysize)

sig := sign(sk, message)

isValid := verify(pk, message, sig)

Public keys as Identities

A useful trick as Bitcoin do

A Simple Cryptocurrency Example

GoofyCoin
1.Goofy, can create new coins whenever he wants and these newly created coins belong to him
2.whoever owns a coin can transfer it on to someone else

double‐spending attack — Alice is spending the same coin twice.
ScroogeCoin
Scrooge publishes an append‐only ledger containing the history of all the transactions that have happened.
ScroogeCoin block chain.

CreateCoins transaction.

A PayCoins Transaction.