Extract public key from private key pem using only nodejs/javascript

Question

Using nodejs and only javascript, how do I extract a public key from a private key pem?

The private key that I have in hand is a PEM formatted private key; I'd like to extract the public key so I can distribute it to collaborators.

I regularly use the pure javascript node-forge module but have not yet discovered how to extract the public key from the private key.

I am also aware of, and presently use the ursa module to accomplish this; but I would like a pure javascript or pure nodejs solution if available.

Answer 1

Modern answer NodeJS v11.6.0 (released Dec 2018)

You do not need any external packages

https://nodejs.org/api/crypto.html

const crypto = require('crypto')
const fs = require('fs')

// assuming you have a private.key file that begins with '-----BEGIN RSA PRIVATE KEY-----...'
const privateKey = fs.readFileSync('./private.key')

const pubKeyObject = crypto.createPublicKey({
    key: privateKey,
    format: 'pem'
})

const publicKey = pubKeyObject.export({
    format: 'pem',
    type: 'spki'
})

// -----BEGIN PUBLIC KEY-----... 
console.log(publicKey)  

Answer 2

from the node-forge documentation

pem = '-----PRIVATE KEY ----- [...]'
pki = require('node-forge').pki
privateKey = pki.privateKeyFromPem(pem)
publicKey  = pki.setRsaPublicKey(privateKey.n, privateKey.e)
console.log(pki.publicKeyToPem(publicKey))