android -------- RSA加密解密算法

RSA加密算法是一种非对称加密算法。在公开密钥加密和电子商业中RSA被广泛使用

RSA公开密钥密码体制。所谓的公开密钥密码体制就是使用不同的加密密钥与解密密钥，是一种“由已知加密密钥推导出解密密钥在计算上是不可行的”密码体制

网上写法也有很多种，分享一种参考

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;

    }

}

main方法

 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();

        System.out.println(modulus);

        //公钥指数

        String public_exponent = publicKey.getPublicExponent().toString();

        //私钥指数

        String private_exponent = privateKey.getPrivateExponent().toString();

        System.out.println("公钥指数:"+public_exponent);

        System.out.println("私钥指数:"+private_exponent);

        //明文

        String ming = "123456789 Hello 小笨蛋";

        //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.out.println("加密后的密文"+mi);

        //解密后的明文

        String mingn = RSAUtils.decryptByPrivateKey(mi, priKey);

        System.out.println("解密后的明文"+mingn);

    }

日志（编码太长没截取完）

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android -------- RSA加密解密算法

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