加密工具类

import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;
    public static String addSign(String mchnt_key, String signStr) {
        String RSA = "";
        try {
            byte[] bytesKey = (new BASE64Decoder()).decodeBuffer(mchnt_key.trim());
            PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(bytesKey);
            KeyFactory keyFactory = KeyFactory.getInstance("RSA");
            PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);
            Signature signature = Signature.getInstance("MD5WithRSA");
            signature.initSign(priKey);
            signature.update(signStr.toString().getBytes("GBK"));
            RSA = (new BASE64Encoder()).encodeBuffer(signature.sign());
        } catch (Exception e) {
            e.printStackTrace();
        }
        return RSA;
    }