Ethereum: How OP_CHECKSIG Works

Understanding OP_CHECKSIG: The Power of Private Key Signatures in Ethereum

For beginners learning about Bitcoin, scripting, and public-key cryptography (P2PKH), it’s important to understand the concept of “OP_CHECKSIG.” In this article, we’ll dive 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. This verifies the authenticity and integrity of a transaction and ensures that the sender is in control of 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 passed through the “OP_CHECKSIG” opcode. The EVM checks the signature against a known public key stored on the blockchain, ensuring that the sender has control over the funds.

Here’s a step-by-step breakdown 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 change the contents of the transaction.

• Signature Creation: The EVM generates a signature for the transaction, which is a unique identifier representing 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 opcode

  : The “OP_CHECKSIG” opcode is applied to the signed transaction, verifying its integrity and authenticity.

• Public key verification: The EVM verifies the signature against a public key stored in the blockchain (e.g. the address “0x…”). This ensures that:

• The sender has control over the funds transferred

• The signature is valid for the specific transaction

Example code

Pragma solidity ^0,8.0;
contract signer {
function signTransaction(address of, uint amount) public {
// Generate a private key using keccak256
bytes32 privateKey = keccak256(abi.encodePacked(of));
// Encrypt the transaction data using the privateKey
bytes storage transactionData = abi.encodePacked(amount);
// Sign the transaction using the private key
bytes32 signature = keccak256(abi.encodePacked(privateKey, transactionData));
// 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(publicKey, signature))
// Verify that the signature matches the expected public key and transaction data
if (sig == publicKey) {
returns true;
} else {
returns false;
}
}
}
}

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

Conclusion

In summary, “OP_CHECKSIG” is an essential opcode in the Ethereum Virtual Machine that allows developers to sign transactions with their private keys. By verifying the signature against a public key stored on the blockchain, the EVM ensures that the sender has control over the funds transferred. This fundamental concept is crucial for secure and trustless transaction processing on the Ethereum network.

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