import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.InputStream;

import java.security.KeyFactory;

import java.security.PrivateKey;

import java.security.PublicKey;

import java.security.spec.PKCS8EncodedKeySpec;

import java.security.spec.X509EncodedKeySpec;

import javax.crypto.Cipher;

public class RSA{

	public static final String  SIGN_ALGORITHMS = "SHA1WithRSA";

	/**

	* RSA签名

	* @param content 待签名数据

	* @param privateKey 商户私钥

	* @param input_charset 编码格式

	* @return 签名值

	*/

	public static String sign(String content, String privateKey, String input_charset)

	{

        try

        {

        	PKCS8EncodedKeySpec priPKCS8 	= new PKCS8EncodedKeySpec( Base64.decode(privateKey) );

        	KeyFactory keyf 				= KeyFactory.getInstance("RSA");

        	PrivateKey priKey 				= keyf.generatePrivate(priPKCS8);

            java.security.Signature signature = java.security.Signature

                .getInstance(SIGN_ALGORITHMS);

            signature.initSign(priKey);

            signature.update( content.getBytes(input_charset) );

            byte[] signed = signature.sign();

            return Base64.encode(signed);

        }

        catch (Exception e)

        {

        	e.printStackTrace();

        }

        return null;

    }

	/**

	* RSA验签名检查

	* @param content 待签名数据

	* @param sign 签名值

	* @param ali_public_key 支付宝公钥

	* @param input_charset 编码格式

	* @return 布尔值

	*/

	public static boolean verify(String content, String sign, String ali_public_key, String input_charset)

	{

		try

		{

			KeyFactory keyFactory = KeyFactory.getInstance("RSA");

	        byte[] encodedKey = Base64.decode(ali_public_key);

	        PublicKey pubKey = keyFactory.generatePublic(new X509EncodedKeySpec(encodedKey));

			java.security.Signature signature = java.security.Signature

			.getInstance(SIGN_ALGORITHMS);

			signature.initVerify(pubKey);

			signature.update( content.getBytes(input_charset) );

			boolean bverify = signature.verify( Base64.decode(sign) );

			return bverify;

		}

		catch (Exception e)

		{

			e.printStackTrace();

		}

		return false;

	}

	/**

	* 解密

	* @param content 密文

	* @param private_key 商户私钥

	* @param input_charset 编码格式

	* @return 解密后的字符串

	*/

	public static String decrypt(String content, String private_key, String input_charset) throws Exception {

        PrivateKey prikey = getPrivateKey(private_key);

        Cipher cipher = Cipher.getInstance("RSA");

        cipher.init(Cipher.DECRYPT_MODE, prikey);

        InputStream ins = new ByteArrayInputStream(Base64.decode(content));

        ByteArrayOutputStream writer = new ByteArrayOutputStream();

        //rsa解密的字节大小最多是128，将需要解密的内容，按128位拆开解密

        byte[] buf = new byte[128];

        int bufl;

        while ((bufl = ins.read(buf)) != -1) {

            byte[] block = null;

            if (buf.length == bufl) {

                block = buf;

            } else {

                block = new byte[bufl];

                for (int i = 0; i < bufl; i++) {

                    block[i] = buf[i];

                }

            }

            writer.write(cipher.doFinal(block));

        }

        return new String(writer.toByteArray(), input_charset);

    }

	/**

	* 得到私钥

	* @param key 密钥字符串（经过base64编码）

	* @throws Exception

	*/

	public static PrivateKey getPrivateKey(String key) throws Exception {

		byte[] keyBytes;

		keyBytes = Base64.decode(key);

		PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);

		KeyFactory keyFactory = KeyFactory.getInstance("RSA");

		PrivateKey privateKey = keyFactory.generatePrivate(keySpec);

		return privateKey;

	}

}