encrypt decrypt file in react-native using rn-fetch-blob

// App.js root project
using rn-fetch-blob,node-forge, and buffer

import React from 'react';
import { StyleSheet, Text, View, PermissionsAndroid } from 'react-native';
import RNFS from 'react-native-fs';
import RNFetchBlob from 'rn-fetch-blob'
import forge from 'node-forge';
import {Buffer} from 'buffer';

const fs = RNFetchBlob.fs;

export default class App extends React.Component {
  async componentWillMount(){
    try {
      const granted = await PermissionsAndroid.requestMultiple([
        PermissionsAndroid.PERMISSIONS.READ_EXTERNAL_STORAGE,
        PermissionsAndroid.PERMISSIONS.WRITE_EXTERNAL_STORAGE,
        PermissionsAndroid.PERMISSIONS.CAMERA,
      ])
    }catch (e){
      console.warn(e)
    }
  }
  // componentDidMount(){

  // }
  render(){
    var key = forge.random.getBytesSync(16);
    var iv = forge.random.getBytesSync(16);
    var bufferSize = 1024*64;
    var cipher = forge.cipher.createCipher('AES-CBC', key);
    cipher.start({iv: iv});
    var decipher = forge.cipher.createDecipher('AES-CBC', key);
    decipher.start({iv: iv});


    fs.ls(fs.dirs.DownloadDir)
    .then(res=>{
      fs.readStream('/sdcard/Download/d1.pdf','ascii',bufferSize)
      .then(stream=>{
        var c = [];
        stream.open();
        stream.onData(chunk=>{
          c = c.concat(chunk)
        })
        stream.onEnd(()=>{
          console.log('c',c)
          // fs.writeFile('/sdcard/Download/2.copy.copy.png', c, 'ascii').then(()=>{console.log('copycopy')}) //this is working guys
      
          cipher.update(forge.util.createBuffer(c,'utf8'));
          cipher.finish();
          var encrypted = cipher.output;
          // console.log('encrypted : ',encrypted)
          // console.log('encrypted array : ',Array.from(Buffer.from(encrypted.getBytes())))
          fs.writeFile('/sdcard/Download/d1.pdf.enc',Array.from(Buffer.from(encrypted.getBytes())),'ascii')
          .then(()=>{
            console.log("FILE ENCRYPTED")
            fs.readFile('/sdcard/Download/d1.pdf.enc','ascii')
            .then(data=>{
              console.log('data: ',data)
              decipher.update(forge.util.createBuffer(data,'utf8'));
              var result = decipher.finish();
              var array_decrypted = Array.from(decipher.output.getBytes());
              fs.writeFile('/sdcard/Download/d1.copy.dec.pdf', c, 'ascii')
              .then(()=>{console.log('File Already decrypted')})
            })
          })
          console.log("OKE")
        })
      })
    })
    return (
      <View style={styles.container}>
        <Text>Open up App.tsx to start working on your app!</Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});