RSA 非对称加密算法的Java实现

关于RSA的介绍Google一下很多，这里不做说明。项目开发中一般会把公钥放在本地进行加密，服务端通过私钥进行解密。Android项目开发中要用到这个加密算法，总结后实现如下：

import android.content.Context;
import android.util.Base64;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.Key;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

import javax.crypto.Cipher;

public class RSAUtil {

    /**
     * KEY_ALGORITHM
     */
    public static final String KEY_ALGORITHM = "RSA";
    /**
     * 加密Key的长度等于1024
     */
    public static int KEYSIZE = 1024;
    /**
     * 解密时必须按照此分组解密
     */
    public static int decodeLen = KEYSIZE / 8;
    /**
     * 加密时小于117即可
     */
    public static int encodeLen = 110;//(DEFAULT_KEY_SIZE / 8) - 11;

    /**
     * 加密填充方式,android系统的RSA实现是"RSA/None/NoPadding"，而标准JDK实现是"RSA/None/PKCS1Padding" ，这造成了在android机上加密后无法在服务器上解密的原因
     */
    public static final String ECB_PKCS1_PADDING = "RSA/ECB/PKCS1Padding";

    public static final byte[] EMPTY_BYTE_ARRAY = new byte[0];

    /**
     * 通过公钥加密
     */
    public static byte[] encryptPublicKey(byte[] encryptedData, String key) throws Exception {
        if (encryptedData == null) {
            throw new IllegalArgumentException("Input encryption data is null");
        }
        byte[] encode = new byte[]{};
        for (int i = 0; i < encryptedData.length; i += encodeLen) {
            byte[] subarray = subarray(encryptedData, i, i + encodeLen);
            byte[] doFinal = encryptByPublicKey(subarray, key);
            encode = addAll(encode, doFinal);
        }
        return encode;
    }

    /**
     * 通过私钥解密
     */
    public static byte[] decryptPrivateKey(byte[] encode, String key) throws Exception {
        if (encode == null) {
            throw new IllegalArgumentException("Input data is null");
        }
        byte[] buffers = new byte[]{};
        for (int i = 0; i < encode.length; i += decodeLen) {
            byte[] subarray = subarray(encode, i, i + decodeLen);
            byte[] doFinal = decryptByPrivateKey(subarray, key);
            buffers = addAll(buffers, doFinal);
        }
        return buffers;
    }

    /**
     * 从字符串中加载公钥
     *
     * @param publicKeyStr 公钥数据字符串
     */
    private static PublicKey loadPublicKey(String publicKeyStr) throws Exception {
        try {
            byte[] buffer = decode(publicKeyStr);
            KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
            //表示根据 ASN.1 类型 SubjectPublicKeyInfo 进行编码的公用密钥的 ASN.1 编码。
            X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
            return keyFactory.generatePublic(keySpec);
        } catch (NoSuchAlgorithmException e) {
            throw new Exception("无此算法");
        } catch (InvalidKeySpecException e) {
            throw new Exception("公钥非法");
        } catch (NullPointerException e) {
            throw new Exception("公钥数据为空");
        }
    }

    /**
     * 从字符串中加载私钥<br>
     * 加载时使用的是PKCS8EncodedKeySpec（PKCS#8编码的Key指令）。
     */
    private static PrivateKey loadPrivateKey(String privateKeyStr) throws Exception {
        try {
            byte[] buffer = decode(privateKeyStr);
            //表示按照 ASN.1 类型 PrivateKeyInfo 进行编码的专用密钥的 ASN.1 编码。
            PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
            KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
            return keyFactory.generatePrivate(keySpec);
        } catch (NoSuchAlgorithmException e) {
            throw new Exception("无此算法");
        } catch (InvalidKeySpecException e) {
            throw new Exception("私钥非法");
        } catch (NullPointerException e) {
            throw new Exception("私钥数据为空");
        }
    }

    /**
     * 用私钥解密
     */
    private static byte[] decryptByPrivateKey(byte[] data, String key) throws Exception {
        if (data == null) {
            throw new IllegalArgumentException("Input data is null");
        }
        //取得私钥
        Key privateKey = loadPrivateKey(key);
        // 对数据解密
        Cipher cipher = Cipher.getInstance(ECB_PKCS1_PADDING);
        cipher.init(Cipher.DECRYPT_MODE, privateKey);

        return cipher.doFinal(data);
    }

    /**
     * 用公钥加密
     */
    private static byte[] encryptByPublicKey(byte[] data, String key) throws Exception {
        if (data == null) {
            throw new IllegalArgumentException("Input data is null");
        }
        // 取得公钥
        Key publicKey = loadPublicKey(key);
        // 对数据加密
        Cipher cipher = Cipher.getInstance(ECB_PKCS1_PADDING);
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);

        return cipher.doFinal(data);
    }

    /**
     * <p>
     * BASE64字符串解码为二进制数据
     * </p>
     */
    public static byte[] decode(String base64) {
        return Base64.decode(base64, Base64.DEFAULT);
    }

    /**
     * <p>
     * 二进制数据编码为BASE64字符串
     * </p>
     */
    public static String encode(byte[] bytes) {
        return Base64.encodeToString(bytes, Base64.DEFAULT);
    }

    /**
     * <p>Produces a new {@code byte} array containing the elements
     * between the start and end indices.
     *
     * <p>The start index is inclusive, the end index exclusive.
     * Null array input produces null output.
     *
     * @param array               the array
     * @param startIndexInclusive the starting index. Undervalue (&lt;0)
     *                            is promoted to 0, overvalue (&gt;array.length) results
     *                            in an empty array.
     * @param endIndexExclusive   elements up to endIndex-1 are present in the
     *                            returned subarray. Undervalue (&lt; startIndex) produces
     *                            empty array, overvalue (&gt;array.length) is demoted to
     *                            array length.
     * @return a new array containing the elements between
     * the start and end indices.
     * @since 2.1
     */
    private static byte[] subarray(final byte[] array, int startIndexInclusive, int endIndexExclusive) {
        if (array == null) {
            return null;
        }
        if (startIndexInclusive < 0) {
            startIndexInclusive = 0;
        }
        if (endIndexExclusive > array.length) {
            endIndexExclusive = array.length;
        }
        final int newSize = endIndexExclusive - startIndexInclusive;
        if (newSize <= 0) {
            return EMPTY_BYTE_ARRAY;
        }

        final byte[] subarray = new byte[newSize];
        System.arraycopy(array, startIndexInclusive, subarray, 0, newSize);
        return subarray;
    }

    /**
     * <p>Adds all the elements of the given arrays into a new array.
     * <p>The new array contains all of the element of {@code array1} followed
     * by all of the elements {@code array2}. When an array is returned, it is always
     * a new array.
     *
     * @param array1 the first array whose elements are added to the new array.
     * @param array2 the second array whose elements are added to the new array.
     * @return The new byte[] array.
     * @since 2.1
     */
    private static byte[] addAll(final byte[] array1, final byte... array2) {
        if (array1 == null) {
            return clone(array2);
        } else if (array2 == null) {
            return clone(array1);
        }
        final byte[] joinedArray = new byte[array1.length + array2.length];
        System.arraycopy(array1, 0, joinedArray, 0, array1.length);
        System.arraycopy(array2, 0, joinedArray, array1.length, array2.length);
        return joinedArray;
    }

    /**
     * <p>Clones an array returning a typecast result and handling
     * {@code null}.
     *
     * <p>This method returns {@code null} for a {@code null} input array.
     *
     * @param array the array to clone, may be {@code null}
     * @return the cloned array, {@code null} if {@code null} input
     */
    private static byte[] clone(final byte[] array) {
        if (array == null) {
            return null;
        }
        return array.clone();
    }

    /**
     * 读取密钥信息
     */
    public static String readString(InputStream in) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        String readLine = null;
        StringBuilder sb = new StringBuilder();
        while ((readLine = br.readLine()) != null) {
            if (readLine.charAt(0) == '-') {
                continue;
            } else {
                sb.append(readLine);
                sb.append('\r');
            }
        }

        return sb.toString();
    }
}

使用如下：

  /**
     * 获取加密数据
     *
     * @param encryptStr 待加密字符串
     * rsa_public_key.pem 为本地公钥
     */
    public String getEncryptData(Context context, String encryptStr) {

        try {
            InputStream inPublic = context.getResources().getAssets().open("rsa_public_key.pem");
            String publicKey = readString(inPublic);
            byte[] encodedData = encryptPublicKey(encryptStr.getBytes(), publicKey);

            return encode(encodedData);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "";
    }