How does the blockchain know that the transaction sent is not forged?
Transactions are signed and can be verified to be authentic, like so:
For a transaction signature to be created, access to the account and its private key is required. Which is why, we need to unlock our MM, and sign before committing a transaction.
Private Key: 32 bytes (64 hex characters)
Public Key
The public key is generated from a private key, using ECDSA. This is a one-way function, the only way is to brute-force it.
Ethereum Account (Wallet Address)
An Ethereum account is the Keccak Hash of the last 20 bytes (40 hex char) of the public key.
Can go from Private -> Public -> Account. No reverse.
Signing & Verification
The transaction gets signed with the private key, creating additional fields of v,r,s. The signature is the r and s.
You cannot reverse engineer the private key from the signature.
With the r & s, you can run them through an ECRECOVER function, and it will output the Public Khey and Wallet Address (Eth account).
