?main()方法：

public static void main(String[] args) throws Exception {// TODO Auto-generated method stubHashMap<String, Object> map = RSAUtils.getKeys();//生成公鑰和私鑰RSAPublicKey publicKey = (RSAPublicKey) map.get("public");RSAPrivateKey privateKey = (RSAPrivateKey) map.get("private");//模String modulus = publicKey.getModulus().toString();//公鑰指數String public_exponent = publicKey.getPublicExponent().toString();//私鑰指數String private_exponent = privateKey.getPrivateExponent().toString();//明文String ming = "123456789";//使用模和指數生成公鑰和私鑰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);}

RSAUtils.java：

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 {/*** 生成公鑰和私鑰* @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;}/*** 使用模和指數生成RSA公鑰* 注意：【此代碼用了默認補位方式，為RSA/None/PKCS1Padding，不同JDK默認的補位方式可能不同，如Android默認是RSA/None/NoPadding】* @param modulus 模* @param exponent 指數* @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;}}/*** 使用模和指數生成RSA私鑰* 注意：【此代碼用了默認補位方式，為RSA/None/PKCS1Padding，不同JDK默認的補位方式可能不同，如Android默認是RSA/None/NoPadding】* @param modulus 模* @param exponent 指數* @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;}}/*** 公鑰加密* @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);// 模長int key_len = publicKey.getModulus().bitLength() / 8;// 加密數據長度 <= 模長-11String[] datas = splitString(data, key_len - 11);String mi = "";//如果明文長度大于模長-11則要分組加密for (String s : datas) {mi += bcd2Str(cipher.doFinal(s.getBytes()));}return mi;}/*** 私鑰解密* @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);//模長int key_len = privateKey.getModulus().bitLength() / 8;byte[] bytes = data.getBytes();byte[] bcd = ASCII_To_BCD(bytes, bytes.length);System.err.println(bcd.length);//如果密文長度大于模長則要分組解密String ming = "";byte[][] arrays = splitArray(bcd, key_len);for(byte[] arr : arrays){ming += new String(cipher.doFinal(arr));}return ming;}/*** ASCII碼轉BCD碼*/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);elsebcd = (byte) (asc - 48);return bcd;}/*** BCD轉字符串*/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;}/***拆分數組 */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;} }

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