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");