Java Schnorr signatures for curve secp256k1

dependencies {
    // secp256k1
    implementation 'fr.acinq.secp256k1:secp256k1-kmp-jvm:0.10.0'
    runtimeOnly 'fr.acinq.secp256k1:secp256k1-kmp-jni-jvm:0.10.0'

    // okio for string serialize and hex, sha256 digest convert
    implementation 'com.squareup.okio:okio:3.3.0'
}

public interface Key {
  /**
   * encode by key
   */
  String encoded();

  /**
   * for human reading
   */
  String hex();
}

import fr.acinq.secp256k1.Secp256k1;
import java.util.Arrays;
import okio.ByteString;

/**
 * Secret key
 *
 * @param key supported byte[] or string, and it knows how to encode and decode itself as hex, base64, and
 * UTF-8.
 */
public record SecKey(ByteString key) implements Key {

  /**
   * Generated a compress public key.
   * <p>
   * The public key format is [x value 32bits, y value 32bits], so the compress is get the x value to public key.
   *
   * @return {@link PubKey}
   */
  public PubKey pubkey() {
    return new PubKey(ByteString.of(Arrays.copyOfRange(Secp256k1.Companion.pubKeyCompress(
      Secp256k1.Companion.pubkeyCreate(key.toByteArray())), 1, 33)));
  }

  /**
   * Signature data
   *
   * @param payload the data should convert to ByteString
   * @return sign data.
   */
  public ByteString sign(ByteString payload) {
    return ByteString.of(Secp256k1.Companion.signSchnorr(payload.toByteArray(), key.toByteArray(), null));
  }

  @Override
  public String encoded() {
    // todo Bech32 encode
    return null;
  }

  /**
   * for human reading
   *
   * @return hex code
   */
  @Override
  public String hex() {
    return key.hex();
  }
}

import okio.ByteString;

/**
 * Public key
 *
 * @param key supported byte[] or string, and it knows how to encode and decode itself as hex, base64, and
 * UTF-8.
 */
public record PubKey(ByteString key) implements Key {

  @Override
  public String encoded() {
    // we don't use pubkey encode, because pubkey would be upload to others
    return null;
  }

  /**
   * for human reading
   *
   * @return hex code
   */
  @Override
  public String hex() {
    return key.hex();
  }
}

# fake key
PRIVATE_KEY: 1d79a6744cd5617a97dbd7220502d35eb99b9d37689439689a7b71ad4e28303a
PUBLICK_KEY: 1a3731a85dbb00a07b9fdb489a5b4d4bb1df36e12c95cc0aa7ff91747b542217

@Test
void test() {
  final SecKey secKey = new SecKey(ByteString.decodeHex(PRIVATE_KEY));
  final PubKey pubkey = secKey.pubkey();
  Assertions.assertThat(pubkey.hex()).isEqualTo(PUBLICK_KEY);
}

@UtilsClass
public class VerifyUtils {
  /**
   * 驗證簽名
   *
   * @param sig 簽名
   * @param data 被簽名的資料
   * @param pubkey pubkey
   * @return
   */
  public boolean verifySign(ByteString sig, ByteString data, ByteString pubkey) {
    return Secp256k1.Companion.verifySchnorr(sig.toByteArray(), id.toByteArray(), pubkey.toByteArray());
  }
}