Java中RSA加密解密的实现方法分析

public static void main(String[] args) throws Exception {
    // TODO Auto-generated method stub
    HashMap<String, Object> map = RSAUtils.getKeys();
    //生成公钥和私钥
    RSAPublicKey publicKey = (RSAPublicKey) map.get("public");
    RSAPrivateKey privateKey = (RSAPrivateKey) map.get("private");
    //模
    String modulus = publicKey.getModulus().toString();
    //公钥指数
    String public_exponent = publicKey.getPublicExponent().toString();
    //私钥指数
    String private_exponent = privateKey.getPrivateExponent().toString();
    //明文
    String ming = "123456789";
    //使用模和指数生成公钥和私钥
    RSAPublicKey pubKey = RSAUtils.getPublicKey(modulus, public_exponent);
    RSAPrivateKey priKey = RSAUtils.getPrivateKey(modulus, private_exponent);
    //加密后的密文
    String mi = RSAUtils.encryptByPublicKey(ming, pubKey);
    System.err.println(mi);
    //解密后的明文
    ming = RSAUtils.decryptByPrivateKey(mi, priKey);
    System.err.println(ming);
}

package yyy.test.rsa;
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.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()));
    }
    return mi;
  }
  /**
   * 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");
    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;
  }
}

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

Cipher cipher = Cipher.getInstance("RSA/ECB/NoPadding");