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java实现RSA加密和解密

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RSAUtils.java```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') &amp;&amp; (asc <= '9'))
        bcd = (byte) (asc - '0');
    else if ((asc >= 'A') &amp;&amp; (asc <= 'F'))
        bcd = (byte) (asc - 'A' + 10);
    else if ((asc >= 'a') &amp;&amp; (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] &amp; 0xf0) >> 4) &amp; 0x0f);
        temp[i * 2] = (char) (val > 9 ? val + 'A' - 10 : val + '0');

        val = (char) (bytes[i] &amp; 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 &amp;&amp; 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 &amp;&amp; y!=0){
            System.arraycopy(data, i*len, arr, 0, y);
        }else{
            System.arraycopy(data, i*len, arr, 0, len);
        }
        arrays[i] = arr;
    }
    return arrays;
}

}

用法:```java
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);
    }

标签:java

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