java_src/src/main/java/com/google/crypto/tink/subtle/Hex.java

// Copyright 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
////////////////////////////////////////////////////////////////////////////////

package com.google.crypto.tink.subtle;

/**
 * Helper methods for encode/decode hex strings.
 *
 * @since 1.0.0
 */
public final class Hex {
  /** Encodes a byte array to hex. */
  public static String encode(final byte[] bytes) {
    String chars = "0123456789abcdef";
    StringBuilder result = new StringBuilder(2 * bytes.length);
    for (byte b : bytes) {
      // convert to unsigned
      int val = b & 0xff;
      result.append(chars.charAt(val / 16));
      result.append(chars.charAt(val % 16));
    }
    return result.toString();
  }

  /** Decodes a hex string to a byte array. */
  public static byte[] decode(String hex) {
    if (hex.length() % 2 != 0) {
      throw new IllegalArgumentException("Expected a string of even length");
    }
    int size = hex.length() / 2;
    byte[] result = new byte[size];
    for (int i = 0; i < size; i++) {
      int hi = Character.digit(hex.charAt(2 * i), 16);
      int lo = Character.digit(hex.charAt(2 * i + 1), 16);
      if ((hi == -1) || (lo == -1)) {
        throw new IllegalArgumentException("input is not hexadecimal");
      }
      result[i] = (byte) (16 * hi + lo);
    }
    return result;
  }
}