Ethereum: How is the public key extracted from (message, digital signature, address)

Extracting Public Keys from Ethereum Messages: Understanding the Relationship between P2PKH Addresses, Digital Signatures, and Public Keys

Ethereum’s private key (P2PKH) structure is a crucial aspect of its cryptographic mechanism. In this article, we’ll delve into how public keys are extracted from a message, digital signature, and P2PKH address.

The Basics: Ethereum’s Private Key Format

On the Ethereum network, every account has a unique private key (P2PKH), which is a 256-bit (32-byte) compressed version of the user’s wallet’s seed phrase. This seed phrase is used to derive other keys, including the public key and digital signature.

The Relationship between P2PKH Address, Digital Signature, and Public Key

When you sign a message using Ethereum’s digital signature function, the resulting output (digital signature) contains information about your private key. The digital signature is generated by combining the sender’s public key with the sender’s address, along with other cryptographic parameters.

The process involves:

• Signing: You use your private key to generate a digital signature for the message.

• Compression and encoding: The digital signature is compressed and encoded using a specific algorithm (e.g., Base64).

• Recipient public key: Your P2PKH address is used to derive the recipient’s public key.

Extracting the Public Key

Now, let’s examine how you can extract the public key from a message, digital signature, and P2PKH address:

• Digital Signature

  

  : The digital signature generated by your private key contains information about your public key.

• P2PKH Address

  : Your P2PKH address is used to derive the recipient’s public key.

• Public Key (optional): If you want to extract your own public key, you can use the following formula:

Public Key = (Digital Signature XOR Message) ^ Public Key Derivation Function

Here’s a high-level example using Ethereum’s eth_getTransactionReceipt function:

const transaction = transactionFactory.createTransaction(

  {

    from: '0x', // sender address

    to: '0x...', // recipient address

    data: messageData, // message payload

    nonce: txNonce,

    gasPrice: transactionGasPrice,

    gasLimit: txGasLimit,

  }

);


const signature = transaction.getTransactionReceipt().signature;

const publicKey = (signature ^ transaction.getOutput(1).data).toString('hex');


console.log(publicKey);

Important Notes

• This is a simplified explanation of the process. In reality, Ethereum’s private key format and cryptographic algorithms are more complex.

• The public key extraction process assumes that you have the necessary permissions to access and retrieve the recipient’s P2PKH address.

• Keep in mind that extracting your own public key can be sensitive information, as it contains sensitive user data (e.g., wallet balances).

In conclusion, while Ethereum’s private key format involves a unique combination of P2PKH address, digital signature, and message payload, extracting the public key is not straightforward. However, by understanding the relationship between these components, you can gain insights into Ethereum’s cryptographic mechanisms and potentially use this knowledge to develop custom applications or analyze existing data.