java加密算法之RSA篇

    public static byte[] encryptByPrivateKey(byte[] data, String privateKey) {
        try {
            byte[] keyBytes = Mybase64Utils.decodeStringForByte(privateKey);
            PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA_KEY_ALGORITHM);
            Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
            Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
            cipher.init(Cipher.ENCRYPT_MODE, privateK);
            int inputLen = data.length;
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            int offSet = 0;
            byte[] cache;
            int i = 0;
            // 对数据分段加密
            while (inputLen - offSet > 0) {
                if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                    cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
                } else {
                    cache = cipher.doFinal(data, offSet, inputLen - offSet);
                }
                out.write(cache, 0, cache.length);
                i++;
                offSet = i * MAX_ENCRYPT_BLOCK;
            }
            byte[] encryptedData = out.toByteArray();
            out.close();
            return encryptedData;
        }catch (Exception e){

        }
        return null;
    }

    public static byte[] decryptByPublicKey(byte[] encryptedData, String publicKey) {
        try {
            byte[] keyBytes = Mybase64Utils.decodeStringForByte(publicKey);
            X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA_KEY_ALGORITHM);
            Key publicK = keyFactory.generatePublic(x509KeySpec);
            Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
            cipher.init(Cipher.DECRYPT_MODE, publicK);
            int inputLen = encryptedData.length;
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            int offSet = 0;
            byte[] cache;
            int i = 0;
            // 对数据分段解密
            while (inputLen - offSet > 0) {
                if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                    cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
                } else {
                    cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
                }
                out.write(cache, 0, cache.length);
                i++;
                offSet = i * MAX_DECRYPT_BLOCK;
            }
            byte[] decryptedData = out.toByteArray();
            out.close();
            return decryptedData;
        } catch (Exception ex) {

        }
        return null;
    }

    
    public static final String RSA_KEY_ALGORITHM = "RSA";

    
    public static final String SIGNATURE_ALGORITHM = "SHA1WithRSA";
    
    private static final int MAX_ENCRYPT_BLOCK = 117;
    
    private static final int MAX_DECRYPT_BLOCK = 128;