Why the private key is generating different public address

cryptographyellipticprivate-keypublic-keywallets

I'm using that Javascript code to generate three things: private key, public key and public address (last 40 characters from public key):

const EC = require('elliptic').ec;
const ec = new EC('secp256k1');

const key = ec.genKeyPair();
const publicKey = key.getPublic('hex');
const privateKey = key.getPrivate('hex');

console.log();
console.log('Private key: ', privateKey);

console.log();
console.log('Public key (big): ', publicKey);

console.log();
console.log('Public key (shorten): ', publicKey.slice(-40));

Although that code generates a private key, when I import that private key to Metamask (or other Ethereum wallet) it creates a wallet with a different public address than that address previously logged in terminal.

I don't know why it is happening, although I have some guesses about the possibilities:

I could be missing some necessary step when converting from private key to public key (hashing it, maybe?)
or when I'm logging the private and public key on console, each time it's logging from a new instance of the key

Does anyone know why it's happening and how to solve it?

Best Answer

Solved it. The code was generating a valid public address for Bitcoin, not Ethereum. Both Bitcoin and Ethereum have the same process to create a private key, but in order to generate an Ethereum public address from it, it's necessary more complex steps, not presented in that code.

Summary

The code in the question theoretically should not run, as the private key is in hex format and the call to new BigInteger(senderPrivKey) to parse the hex string without the 16 radix specified would result in a thrown exception.

When the code is adjusted to use new BigInteger(senderPrivKey, 16) specifying the base 16 radix, the public key is generated as expected.

The Details

Here is a working example. Save it as TestKey.java, compile and run it.

import java.math.BigInteger;

import org.ethereum.crypto.ECKey;
import org.spongycastle.util.encoders.Hex;

public class TestKey {

    public static void main(String[] args) {
        String senderPrivKey = "c85ef7d79691fe79573b1a7064c19c1a9819ebdbd1faaab1a8ec92344438aaf4";

        BigInteger pk = new BigInteger(senderPrivKey, 16);
        System.out.println("Private key: " + pk.toString(16));

        ECKey key = ECKey.fromPrivate(pk);
        System.out.println("Public key: " + Hex.toHexString(key.getAddress()));
    }
}

And the output when running it:

Private key: c85ef7d79691fe79573b1a7064c19c1a9819ebdbd1faaab1a8ec92344438aaf4
Public key: cd2a3d9f938e13cd947ec05abc7fe734df8dd826

I have used the following maven dependency:

    <dependency>
        <groupId>org.ethereum</groupId>
        <artifactId>ethereumj-core</artifactId>
        <version>1.1.0-RELEASE</version>
        <!--  <type>zip</type>  -->
    </dependency>

I don't know how your code ran, because when I change the following line in the source code above to match your code, the BigInteger(...) constructor is expecting to parse a base 10 number rather than a base 16 number :

        BigInteger pk = new BigInteger(senderPrivKey);

And I get the following exception:

Exception in thread "main" java.lang.NumberFormatException: For input string: "c"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at java.math.BigInteger.<init>(BigInteger.java:461)
    at java.math.BigInteger.<init>(BigInteger.java:597)
    at TestKey.main(TestKey.java:14)

[Ethereum] Ethereum Address vs Public Key

When you are creating a new wallet, what you are doing is creating an account. Every account has a private key and a public key, and are indexed by an address that is where you send the transaction.

The address is the last 20 bytes of the hash of the public key.

According to the documentation:

Every account is defined by a pair of keys, a private key and public key. Accounts are indexed by their address which is derived from the public key by taking the last 20 bytes. Every private key/address pair is encoded in a keyfile.

http://ethdocs.org/en/latest/account-management.html?highlight=address#keyfiles

You can find this post useful:

https://kobl.one/blog/create-full-ethereum-keypair-and-address/

Hope this helps.

Best Answer

Related Solutions

[Ethereum] How to get address from private key in java

Summary

The Details

[Ethereum] Ethereum Address vs Public Key

Related Topic