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/**
 * Copyright 2010 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 net.oauth.jsontoken.crypto;

import org.apache.commons.codec.binary.Base64;

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPublicKeySpec;
import java.util.regex.Pattern;

/**
 * Class that can parse "magic key" RSA public key representations, which are of the form
 * RSA...
 */
public class MagicRsaPublicKey {

  private final PublicKey publicKey;

  /**
   * Public constructor.
   * @param magicKey the serialized key (of the form RSA.modulus.exponent).
   */
  public MagicRsaPublicKey(String magicKey) {
    this.publicKey = parseKey(magicKey);
  }

  /**
   * Returns the public key represented by the "magic" serialized key.
   */
  public PublicKey getKey() {
    return publicKey;
  }

  private static PublicKey parseKey(String magicKey) {
    String[] pieces = magicKey.split(Pattern.quote("."));
    if (pieces.length != 3) {
      throw new IllegalStateException("not a valid magic key: " + magicKey);
    }

    if (!pieces[0].equals("RSA")) {
      throw new IllegalStateException("unkown key type for magic key: " + pieces[0]);
    }

    String modulusString = pieces[1];
    String exponentString = pieces[2];

    byte[] modulusBytes = Base64.decodeBase64(modulusString);
    byte[] exponentBytes = Base64.decodeBase64(exponentString);

    BigInteger modulus = new BigInteger(modulusBytes);
    BigInteger exponent = new BigInteger(exponentBytes);

    RSAPublicKeySpec spec = new RSAPublicKeySpec(modulus, exponent);
    KeyFactory fac;
    try {
      fac = KeyFactory.getInstance("RSA");
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException("RSA key factory missing on platform", e);
    }
    try {
      return fac.generatePublic(spec);
    } catch (InvalidKeySpecException e) {
      throw new IllegalStateException("bad key in descripor doc: " + magicKey, e);
    }
  }
}