java實現RSA加密和解密

RSAUtils.java

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-11
    String[] 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);
    else
        bcd = (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;
}

}
</pre> 

 用法：
public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        HashMap<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);
}

</pre>