原來項目中用openresty nginx+lua實現server,lua調用c動態鏈接庫，來使用openss做簽名，並生成130字節（128簽名+2位自定義字節）長度的文件。

nginx:
  location /get/key {
      content_by_lua_file ‘/data/www/sign.lua‘;
  }

sign.lua

local ffi = require "ffi"
--動態鏈接gen_sig_ex_x.c,load("")名字規則，lib***.so
local gs = ffi.load("sin")

ffi.cdef[[
    
 
int gen_main(char *param,unsigned char *signature)
]]

local param_ = ngx.var.arg_param
if param_ then
    local signature = ffi.new("unsigned char[130]", {})
    local cpsn = ffi.new("char[20]", param_)

    gs.gen_main(param_, signature)
    ngx.header["Content-Disposition"] = "attachment; filename=
 
" .. string.format("%s.%d.key", psn, key)
    ngx.header["Content-Length"] = 130
    ngx.say(ffi.string(signature, 130))
else
    ngx.header.content_type = "text/html" 
    ngx.say("the param is not empty")
end

對於sin.so用c與openssl實現了私鑰簽名，並使用RSA結構秘鑰，為順利得到pkcs8，在程序中通過如下代碼逆化了該格式的私鑰。並通過命令得到公鑰。

OpenSSL> genrsa -out rsa_private_key.pem 1024 #生成私鑰

  //根據RSA結構私鑰構建KEY對象，獲取私鑰公鑰base64：
    FILE *filename = NULL;
    filename = fopen("/data/www/unlock.lua/privateKey.pem", "wb");
    //生成私鑰接口
    PEM_write_RSAPrivateKey(filename, key, NULL, NULL, 0, NULL, NULL);
    fclose(filename);

    unsigned char *n_b = (unsigned char *)calloc(RSA_size(key), sizeof(unsigned char));
    unsigned char *e_b = (unsigned char *)calloc(RSA_size(key), sizeof(unsigned char));

    int n_size = BN_bn2bin(key->n, n_b);
    int b_size = BN_bn2bin(key->e, e_b);

    RSA *pubrsa = RSA_new();
    pubrsa->n = BN_bin2bn(n_b, n_size, NULL);
    pubrsa->e = BN_bin2bn(e_b, b_size, NULL);

    FILE *publicKey = NULL;
    publicKey = fopen("/data/www/unlock.lua/publicKey.pem", "wb");
    PEM_write_RSAPublicKey(publicKey, pubrsa);
    fclose(publicKey);
    RSA_free(pubrsa);

====java實現簽名核心代碼:
package com.smartisan.genkey_sig.util;

import org.apache.commons.codec.binary.Base64;

import java.nio.charset.StandardCharsets;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.Signature;
import java.security.spec.PKCS8EncodedKeySpec;

/**
 * desc:
 *
 * @author [email protected]*********.com
 * @since 2017/8/11
 */
public class RsaUtil {
    public static final String KEY_ALGORITHM = "RSA";
    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

    public static byte[] sign(byte[] data, String privateKey) {
        try {
            byte[] keyBytes = Base64.decodeBase64((privateKey));
            PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
            // KEY_ALGORITHM 指定的加密算法
            KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
            // 取私鑰匙對象
            PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);
            // 用私鑰對信息生成數字簽名
            Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
            signature.initSign(priKey);
            signature.update(data);
            return signature.sign();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    public static byte[] sign(String data, String privateKey) {
        return sign(data.getBytes(StandardCharsets.UTF_8), privateKey);
    }
}

java翻譯lua+c+openssl簽名項目