Node.js function to generate RSA keys using Open SSL - node.js

Question

I'm using Node.js as a server side language and I would like to generate an RSA key pairs for any user that registers himself on my website. I'm using a module called keypair. It's working fine for keys with small sizes but when I generate keys with 2048 in size, it's taking so long to perform it so I would like to use Open SSL directly from Node.js using Node's child_process as described in the script down below :
var cp = require('child_process')
, assert = require('assert');
var privateKey, publicKey;
publicKey = '';
cp.exec('openssl genrsa 2048', function(err, stdout, stderr) {
assert.ok(!err);
privateKey = stdout;
console.log(privateKey);
makepub = cp.spawn('openssl', ['rsa', '-pubout']);
makepub.on('exit', function(code) {
assert.equal(code, 0);
console.log(publicKey);
});
makepub.stdout.on('data', function(data) {
publicKey += data;
});
makepub.stdout.setEncoding('ascii');
makepub.stdin.write(privateKey);
makepub.stdin.end();
});
This is working and more faster in key pairs generation than the Node.js keypair module so the issue I'm having is that I don't understand this code (if it's writing files on the server side and reading keys from them or not?) and I would like to turn this script into a function that returns a JSON or an array as result that holds the public and private key.
So any suggestion is welcome, thank you in advance.

Answer 1

Try this.. Moved the code around a little. Uses tmp file, which is deleted, possibly could be done without the tmp file, but this should work.
var cp = require('child_process')
, assert = require('assert')
, fs = require('fs')
;
// gen pub priv key pair
function genKeys(cb){
// gen private
cp.exec('openssl genrsa 2048', function(err, priv, stderr) {
// tmp file
var randomfn = './' + Math.random().toString(36).substring(7);
fs.writeFileSync(randomfn, priv);
// gen public
cp.exec('openssl rsa -in '+randomfn+' -pubout', function(err, pub, stderr) {
// delete tmp file
fs.unlinkSync(randomfn);
// callback
cb(JSON.stringify({public: pub, private: priv}, null, 4));
});
});
}
genKeys(console.log);

Answer 2

You can simply use the small rsa-json module
It's really easy to use and it's asynchronous:
var createRsaKeys = require('rsa-json');
createRsaKeys({bits: 1024}, function(err, keyPair) {
console.log(keyPair.private);
console.log(keyPair.public);
});
rsa-json does not make a direct uses of OpenSSL RSA_generate_key but uses ssh-keygen (from OpenSSH) which is a wrapper around OpenSSL. There is no direct security difference (see this for more information).
PS: Have a look at the only 48 lines of code composing rsa-json.
If you really want to use OpenSSL, you can have a look at the ursa module but:
It's not asynchronous
Is not maintained, the last commit was from Dec 21, 2012
The project is heavy, it does too much things like sugary stuff (base64 encoding, etc.).
It's have embedded C++ OpenSSL wrapper inside it, initialized during installation.
PS: keypair uses native JS, that's why it's very slow. It's not recommended with Node.js which is not good at performing CPU-intensive operations (but good with non-blocking events).