content: package com.wm.remusic.net;
  
  /**
   * Created by wm on 2016/4/14.
   */
  
  import android.support.annotation.NonNull;
  
  import java.io.UnsupportedEncodingException;
  import java.math.BigInteger;
  import java.security.KeyFactory;
  import java.security.KeyPair;
  import java.security.KeyPairGenerator;
  import java.security.NoSuchAlgorithmException;
  import java.security.interfaces.RSAPrivateKey;
  import java.security.interfaces.RSAPublicKey;
  import java.security.spec.RSAPrivateKeySpec;
  import java.security.spec.RSAPublicKeySpec;
  import java.util.HashMap;
  
  import javax.crypto.Cipher;
  
  public class RSAUtils {
  
      /**
       * 生成公钥和私钥
       *
       * @throws NoSuchAlgorithmException
       */
      public static HashMap<String, Object> getKeys() throws NoSuchAlgorithmException {
          HashMap<String, Object> map = new HashMap<String, Object>();
          KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
          keyPairGen.initialize(1024);
          KeyPair keyPair = keyPairGen.generateKeyPair();
          RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
          RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
          map.put("public", publicKey);
          map.put("private", privateKey);
          return map;
      }
  
      /**
       * 使用模和指数生成RSA公钥
       * 注意：【此代码用了默认补位方式，为RSA/None/PKCS1Padding，不同JDK默认的补位方式可能不同，如Android默认是RSA
       * /None/NoPadding】
       *
       * @param modulus  模
       * @param exponent 指数
       * @return
       */
      public static RSAPublicKey getPublicKey(String modulus, String exponent) {
          try {
              BigInteger b1 = new BigInteger(modulus);
              BigInteger b2 = new BigInteger(exponent);
              KeyFactory keyFactory = KeyFactory.getInstance("RSA");
              RSAPublicKeySpec keySpec = new RSAPublicKeySpec(b1, b2);
              return (RSAPublicKey) keyFactory.generatePublic(keySpec);
          } catch (Exception e) {
              e.printStackTrace();
              return null;
          }
      }
  
      /**
       * 使用模和指数生成RSA私钥
       * 注意：【此代码用了默认补位方式，为RSA/None/PKCS1Padding，不同JDK默认的补位方式可能不同，如Android默认是RSA
       * /None/NoPadding】
       *
       * @param modulus  模
       * @param exponent 指数
       * @return
       */
      public static RSAPrivateKey getPrivateKey(String modulus, String exponent) {
          try {
              BigInteger b1 = new BigInteger(modulus);
              BigInteger b2 = new BigInteger(exponent);
              KeyFactory keyFactory = KeyFactory.getInstance("RSA");
              RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec(b1, b2);
              return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
          } catch (Exception e) {
              e.printStackTrace();
              return null;
          }
      }
  
      /**
       * 公钥加密
       *
       * @param data
       * @param publicKey
       * @return
       * @throws Exception
       */
      public static String encryptByPublicKey(String data, RSAPublicKey publicKey)
              throws Exception {
          // Cipher cipher = Cipher.getInstance("RSA");
          Cipher cipher =
                  Cipher.getInstance("RSA/ECB/NoPadding");
          cipher.init(Cipher.ENCRYPT_MODE, publicKey);
  //        // 模长
  //        int key_len = publicKey.getModulus().bitLength() / 8;
  //        // 加密数据长度 <= 模长-11
  //        String[] datas = splitString(data, key_len - 11);
  //        String mi = "";
  //        //如果明文长度大于模长-11则要分组加密
  //        for (String s : datas) {
  //            mi += bcd2Str(cipher.doFinal(s.getBytes()));
  //        }
          String mi = "";
          mi = toHex(cipher.doFinal(data.getBytes()));
          return mi;
      }
  
      @NonNull
      static public String toHex(byte[] c) throws UnsupportedEncodingException {
  
          StringBuilder buf = new StringBuilder();
          for (byte b : c) {
              buf.append(Integer.toHexString(b & 0xff));
          }
          return buf.toString();
      }
  
      /**
       * 私钥解密
       *
       * @param data
       * @param privateKey
       * @return
       * @throws Exception
       */
      public static String decryptByPrivateKey(String data, RSAPrivateKey privateKey)
              throws Exception {
          Cipher cipher = Cipher.getInstance("RSA/ECB/NoPadding");
          cipher.init(Cipher.DECRYPT_MODE, privateKey);
          //模长
          int key_len = privateKey.getModulus().bitLength() / 8;
          byte[] bytes = data.getBytes();
          byte[] bcd = ASCII_To_BCD(bytes, bytes.length);
          System.err.println(bcd.length);
          //如果密文长度大于模长则要分组解密
          String ming = "";
          byte[][] arrays = splitArray(bcd, key_len);
          for (byte[] arr : arrays) {
              ming += new String(cipher.doFinal(arr));
          }
          return ming;
      }
  
      /**
       * ASCII码转BCD码
       */
      public static byte[] ASCII_To_BCD(byte[] ascii, int asc_len) {
          byte[] bcd = new byte[asc_len / 2];
          int j = 0;
          for (int i = 0; i < (asc_len + 1) / 2; i++) {
              bcd[i] = asc_to_bcd(ascii[j++]);
              bcd[i] = (byte) (((j >= asc_len) ? 0x00 : asc_to_bcd(ascii[j++])) + (bcd[i] << 4));
          }
          return bcd;
      }
  
      public static byte asc_to_bcd(byte asc) {
          byte bcd;
  
          if ((asc >= '0') && (asc <= '9'))
              bcd = (byte) (asc - '0');
          else if ((asc >= 'A') && (asc <= 'F'))
              bcd = (byte) (asc - 'A' + 10);
          else if ((asc >= 'a') && (asc <= 'f'))
              bcd = (byte) (asc - 'a' + 10);
          else
              bcd = (byte) (asc - 48);
          return bcd;
      }
  
      /**
       * BCD转字符串
       */
      public static String bcd2Str(byte[] bytes) {
          char temp[] = new char[bytes.length * 2], val;
  
          for (int i = 0; i < bytes.length; i++) {
              val = (char) (((bytes[i] & 0xf0) >> 4) & 0x0f);
              temp[i * 2] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
  
              val = (char) (bytes[i] & 0x0f);
              temp[i * 2 + 1] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
          }
          return new String(temp);
      }
  
      /**
       * 拆分字符串
       */
      public static String[] splitString(String string, int len) {
          int x = string.length() / len;
          int y = string.length() % len;
          int z = 0;
          if (y != 0) {
              z = 1;
          }
          String[] strings = new String[x + z];
          String str = "";
          for (int i = 0; i < x + z; i++) {
              if (i == x + z - 1 && y != 0) {
                  str = string.substring(i * len, i * len + y);
              } else {
                  str = string.substring(i * len, i * len + len);
              }
              strings[i] = str;
          }
          return strings;
      }
  
      /**
       * 拆分数组
       */
      public static byte[][] splitArray(byte[] data, int len) {
          int x = data.length / len;
          int y = data.length % len;
          int z = 0;
          if (y != 0) {
              z = 1;
          }
          byte[][] arrays = new byte[x + z][];
          byte[] arr;
          for (int i = 0; i < x + z; i++) {
              arr = new byte[len];
              if (i == x + z - 1 && y != 0) {
                  System.arraycopy(data, i * len, arr, 0, y);
              } else {
                  System.arraycopy(data, i * len, arr, 0, len);
              }
              arrays[i] = arr;
          }
          return arrays;
      }
  }