Expose hardened bit in Bip32ECKeyPair for other libraries

[macalinao]

https://github.com/web3j/web3j/blob/master/crypto/src/main/java/org/web3j/crypto/Bip32ECKeyPair.java

Is there a reason why the hardened bit is package-private? It's needed to actually derive HD wallet keys.

[macalinao]

For future readers that are trying to use web3j to generate bip44 hdwallets, here's my scala code to do so:

import java.security.SecureRandom
import abacus.server.util.StringUtils
import org.web3j.crypto._

object Wallets {

  val HardenedBit = 0x80000000
  // no idea why this is private.

  val random = new SecureRandom()

  def generateMnemonicAndPassphrase(): (String, String) = {
    val initialEntropy = new Array[Byte](16)
    random.nextBytes(initialEntropy)
    val mnemonic = MnemonicUtils.generateMnemonic(initialEntropy)
    val passphrase = StringUtils.secureAlphanumeric(32)
    (mnemonic, passphrase)
  }

  def generateMasterKey(
    mnemonic: String,
    passphrase: String,
  ): Bip32ECKeyPair = {
    val seed = MnemonicUtils.generateSeed(mnemonic, passphrase)
    Bip32ECKeyPair.generateKeyPair(seed)
  }

  def generateKeyCredentials(
    mnemonic: String,
    passphrase: String,
    index: Int,
  ): Credentials = {
    // ledger does things this way according to
    // https://github.com/ethereum/EIPs/issues/84#issuecomment-406324344
    val path =
      Array[Int](44 | HardenedBit, 60 | HardenedBit, index | HardenedBit, 0, 0)
    Credentials.create(
      Bip32ECKeyPair.deriveKeyPair(
        generateMasterKey(mnemonic, passphrase),
        path,
      ),
    )
  }

}

[MDhondt]

I too vote to make this HARDENED_BIT a public field.

In Java:

public ECKeyPair generateKeyPair(String mnemonic, String passphrase, String derivationPath) {
    int HARDENED_BIT = 0x80000000; // This should be statically importable from org.web3j.crypto.Bip32ECKeyPair

    Integer purpose, coinType, account, change, addressIndex; // parse derivationPath

    Bip32ECKeyPair masterKeypair = Bip32ECKeyPair.generateKeyPair(MnemonicUtils.generateSeed(mnemonic, passphrase));
    int[] path = {purpose | HARDENED_BIT, coinType | HARDENED_BIT, account | HARDENED_BIT, change, addressIndex};
    return Bip32ECKeyPair.deriveKeyPair(masterKeypair, path);
}