status-keycard-java/lib/src/main/java/im/status/keycard/applet/KeyPath.java

package im.status.keycard.applet;

import java.util.StringTokenizer;

/**
 * Keypath object to be used with the KeycardCommandSet
 */
public class KeyPath {
  private int source;
  private byte[] data;

  /**
   * Parses a keypath into a byte array and source parameter to be used with the KeycardCommandSet object.
   *
   * A valid string is composed of a minimum of one and a maximum of 11 components separated by "/".
   *
   * The first component can be either "m", indicating the master key, "..", indicating the parent of the current key,
   * or "." indicating the current key. It can also be omitted, in which case it is considered the same as being ".".
   *
   * All other components are positive integers fitting in 31 bit, eventually suffixed by an apostrophe (') sign,
   * which indicates an hardened key.
   *
   * An example of a valid path is "m/44'/0'/0'/0/0"
   *
   *
   * @param keypath the keypath as a string
   */
  public KeyPath(String keypath) {
    StringTokenizer tokenizer = new StringTokenizer(keypath, "/");

    String sourceOrFirstElement = tokenizer.nextToken();

    switch(sourceOrFirstElement) {
      case "m":
        source = KeycardCommandSet.DERIVE_P1_SOURCE_MASTER;
        break;
      case "..":
        source = KeycardCommandSet.DERIVE_P1_SOURCE_PARENT;
        break;
      case ".":
        source = KeycardCommandSet.DERIVE_P1_SOURCE_CURRENT;
        break;
      default:
        source = KeycardCommandSet.DERIVE_P1_SOURCE_CURRENT;
        tokenizer = new StringTokenizer(keypath, "/"); // rewind
        break;
    }

    int componentCount = tokenizer.countTokens();
    if (componentCount > 10) {
      throw new IllegalArgumentException("Too many components");
    }

    data = new byte[4 * componentCount];

    for (int i = 0; i < componentCount; i++) {
      long component = parseComponent(tokenizer.nextToken());
      writeComponent(component, i);
    }
  }

  public KeyPath(byte[] data, int source) {
    this.data = data;
    this.source = source;
  }

  public KeyPath(byte[] data) {
    this(data, KeycardCommandSet.DERIVE_P1_SOURCE_MASTER);
  }

  private long parseComponent(String num) {
    long sign;

    if (num.endsWith("'")) {
      sign = 0x80000000L;
      num = num.substring(0, (num.length() - 1));
    } else {
      sign = 0L;
    }

    if (num.startsWith("+") || num.startsWith("-")) {
      throw new NumberFormatException("No sign allowed");
    }
    return (sign | Long.parseLong(num));
  }

  private void writeComponent(long component, int i) {
    int off = (i*4);
    data[off] = (byte)((component >> 24) & 0xff);
    data[off + 1] = (byte)((component >> 16) & 0xff);
    data[off + 2] = (byte)((component >> 8) & 0xff);
    data[off + 3] = (byte)(component & 0xff);
  }

  /**
   * The source of the derive command.
   *
   * @return the source of the derive command
   */
  public int getSource() {
    return source;
  }

  /**
   * The byte encoded key path.
   *
   * @return byte encoded key path
   */
  public byte[] getData() {
    return data;
  }

  @Override
  public String toString() {
    StringBuffer sb = new StringBuffer();

    switch(source) {
      case KeycardCommandSet.DERIVE_P1_SOURCE_MASTER:
        sb.append('m');
        break;
      case KeycardCommandSet.DERIVE_P1_SOURCE_PARENT:
        sb.append("..");
        break;
      case KeycardCommandSet.DERIVE_P1_SOURCE_CURRENT:
        sb.append('.');
        break;
    }

    for (int i = 0; i < this.data.length; i += 4) {
      sb.append('/');
      appendComponent(sb, i);
    }

    return sb.toString();
  }

  private void appendComponent(StringBuffer sb, int i) {
    int num = ((this.data[i] & 0x7f) << 24) | ((this.data[i+1] & 0xff) << 16) | ((this.data[i+2] & 0xff) << 8) | (this.data[i+3] & 0xff);
    sb.append(num);

    if ((this.data[i] & 0x80) == 0x80) {
      sb.append('\'');
    }
  }
}