Ethereum: How does OP_CHECKSIG work?

Understanding OP_CHECKSIG: The Power of Private Key Signatures in Ethereum

As a beginner learning about Bitcoin, scripting, and public-key cryptography (P2PKH), it’s important to understand the concept of OP_CHECKSIG. In this article, we’ll delve into the world of private key signing on the Ethereum blockchain.

What is OP_CHECKSIG?

OP_CHECKSIG is a special opcode in the Ethereum Virtual Machine (EVM) that allows developers to sign transactions with their private keys. It’s used to verify the authenticity and integrity of a transaction, ensuring that the sender has control over the funds being transferred.

How ​​does OP_CHECKSIG work?

When a user signs a transaction with their private key, they encrypt it with a checksum, which is then transmitted via the OP_CHECKSIG opcode. The EVM verifies the signature with a known public key stored on the blockchain, ensuring that the sender has control over the funds.

Here is a detailed description of how OP_CHECKSIG works:

• Transaction Creation: When a user wants to send funds to another node on the network, they create a transaction using their private key.

• Encryption: The transaction is then encrypted using a checksum (e.g. ECDSA-256). This ensures that the sender cannot tamper with or alter the contents of the transaction.

• Signature Creation: The EVM generates a signature for the transaction, which is a unique identifier that represents the sender’s private key. This signature includes:

• The sender’s public address (also known as the “from” address)

• The sender’s hash of the encrypted transaction data

• OP_CHECKSIG Operation Code: The OP_CHECKSIG operation code is applied to the signed transaction, which verifies its integrity and authenticity.

• Public Key Verification: The EVM verifies the signature with the public key stored in the blockchain (e.g., address 0x…'). This ensures that:

solidity pragma ^0.8.0;
signatory contract {
function signTransaction(from address, uint amount) public {
// Generate the private key with keccak256
bytes32 privateKey = keccak256(abi.encodePacked(from));
// Encrypt transaction data with private key
bytes transactionData = abi.encodePacked(amount);
// Sign transaction with private key
bytes32 signature = keccak256(abi.encodePacked(privateKey, transactionData));
// Apply OP_CHECKSIG to signed transaction
assembly {
// Check if sender has control over transferred funds
let public_key := 0x...; // Replace with a valid public key
let sig = keccak256(abi.encodePacked(public_key, signature))
// Check if signature matches expected public key and transaction data
if (sig == public_key) {
return true;
} else {
return false;
}
}
}
}
}

In this example, we use the Signercontract to sign the transaction with our private key. ThesignTransactionfunction generates a private key using keccak256, encrypts the transaction data, signs it with the private key, and appliesOP_CHECKSIGto verify its integrity.

In summary,OP_CHECKSIG` is a core operational code in the Ethereum Virtual Machine that allows developers to sign transactions using their private keys. By verifying the signature against the public key stored on the blockchain, the EVM ensures that the sender has control over the transferred funds. This basic concept is key to processing secure and trustless transactions on the Ethereum network.