node.js - Generate Key for signing within nodejs -

i have seems rather simple problem, never had deal cryptography in nodejs before.
want implement system generates new keypair every 4 months, used signing , verifying generated result.
current code:

'use strict'; const fs = require('fs'); const crypto = require('crypto'); const algorithm = 'rsa-sha512'; const sign = crypto.createsign(algorithm); const verify = crypto.createverify(algorithm); const base64 = 'base64'; const keydir = './keys/';  const validator = {};  validator.check = function(dataarray, signature, date){   verify.update(buffer.from(dataarray));   return verify.verify(getpublickey(date), signature); };  validator.sign = function(dice){   sign.update(buffer.from(dice));   return sign.sign(getprivatekey(), base64);//error happens here };  validator.getpublickey = function(date){   date = todateobject(date);   for(current of getfilesdescending()){     if(filenametodate(current).getmilliseconds() <= date.getmilliseconds()){     const prefix = '-----begin rsa public key-----';     const suffix = '-----end rsa public key-----';       return prefix + fs.readfilesync(keydir + filename, 'utf8').split('\n')[0] + suffix;     }   } }  function filenametodate(filename){   const array = filename.split("-");   return new date(array[0], parseint(array[1]) - 1); }  function getprivatekey(){   const file = getfilesdescending()[0];   if(!file || monthdiff(new date(), filenametodate(file)) > 4){     generatekeys();     return getprivatekey();   }   const prefix = '-----begin rsa private key-----';   const suffix = '-----end rsa private key-----';   return prefix + fs.readfilesync(keydir + file, 'utf8').split('\n')[1] + suffix; }  function monthdiff(d1, d2) {     var months;     months = (d2.getfullyear() - d1.getfullyear()) * 12;     months -= d1.getmonth() + 1;     months += d2.getmonth();     return months; }  function getfilesdescending(){   return fs.readdirsync(keydir).sort().reverse(); }  function getmonth(date){   return ('0' + (date.getmonth()+1)).slice(-2) }  function generatekeys(){   const filename = getfilename();   if(!fs.existssync(filename)){     const diffiehell = crypto.creatediffiehellman(1024);//todo change value stronger 1     diffiehell.generatekeys(base64);     fs.writefilesync(filename, diffiehell.getpublickey(base64) + '\n' + diffiehell.getprivatekey(base64));     return true;   }   return false; }  function getfilename(){   const = new date();   return keydir + now.getfullyear() + '-' + getmonth(now); }  function todateobject(date){   return date.from(date) || new date(); }  module.exports = validator; 

basically whenever sign method invoked, code checks if there keypair fiñe generated within last 4 months , if not generate such keypair , use one. data param iso string returned date.toisostring().
i'm getting following error: error: error:0d07207b:asn1 encoding routines:asn1_get_object:header long.
2 questions: i'm probaly doing obvious wrong here, should instead?
, should dump attempt entirely , use https certificates instead?
i'd prefer not because makes local testing lot harder.