decriptar.js

var rsa = require('rsa-stream');
var fs = require('fs');
var privkey = fs.readFileSync('./minhaPrivKey.key', 'utf8');
var encStream = rsa.decrypt(privkey);
var inStream = fs.createReadStream('./foto.enc');
var outStream = fs.createWriteStream('./minhafotolocodedoida.jpg');

inStream.pipe(encStream).pipe(outStream);

encriptar.js

var rsa = require('rsa-stream');
var fs = require('fs');
var pubkey = fs.readFileSync('./minhaPubKey.pub', 'utf8');
var encStream = rsa.encrypt(pubkey);
var inStream = fs.createReadStream('./minhafotolocodedoida.jpg');
var outStream = fs.createWriteStream('./foto.enc');

inStream.pipe(encStream).pipe(outStream);