Ethereum: How does OP

Understanding OP_CHECKSIG: The Power of Private Key Signing in Ethereum

As a beginner to Bitcoin, Scripting, and Public Key Cryptography (P2PKH), it is essential to understand the concept of “OP_CHECKSIG”. In this article, we will delve into the world of private key signatures 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 is 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, it encrypts it with a checksum, which is then passed in the OP_CHECKSIG opcode. The EVM verifies the signature with a known public key stored on the blockchain, ensuring that the sender is in control of the funds.

Here is a step-by-step breakdown of how OP_CHECKSIG works:

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

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

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

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

The sender’s digest of the encrypted transaction data

OP_CHECKSIG operation code: The OP_CHECKSIG operation code is applied to the signed transaction, verifying its integrity and authenticity.

Public key verification

: The EVM verifies the signature against the public key stored in the blockchain (for example, “0x…”). This ensures that:

The sender has control over the funds being transferred

The signature is valid for that transaction

Sample code


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

In this example, we use a “Signer” contract to sign the transaction with its private key. The “signTransaction” function creates a private key using keccak256, encrypts the transaction data, signs it with the private key, and applies the OP_CHECKSIG command to verify integrity.

Conclusion

In summary, OP_CHECKSIG is a core opcode in the Ethereum virtual machine that allows developers to sign transactions with their private keys. By verifying the signature with a public key stored on the blockchain, EVM ensures that the sender controls the funds being transferred. This fundamental concept is key to processing secure and reliable transactions on the Ethereum network.