Using node.js crypto to verify signatures

Question

I am trying to use AWS lambda to verify signatures created with sec256r1 in swift.

Message: "some text to sign"

Has been hashed with sha256 too

signatures will be in base64

encoding:MEYCIQCPfWhpzxMqu3gZWflBm5V0aetgb2/S+SGyGcElaOjgdgIhALaD4lbxVwa8HUUBFOLz+CGvIioDkf9oihSnXHCqh8yV

and public key will look like so:

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXIvPbzLjaPLd8jgiv1TL/X8PXpJN
gDkGRj9U9Lcx1yKURpQFVavcMkfWyO8r7JlZNMax0JKfLZUM1IePRjHlFw==
-----END PUBLIC KEY-----

To clarify,

I am trying to use lambda to verify signatures that come from the client side, and encrypt data with their public key if need be.

Here is code:

    const crypto = require('crypto');
    const verify = crypto.createVerify('SHA256');

    verify.write('some text to sign');
    verify.end();

    const l1 = "-----BEGIN PUBLIC KEY-----\n"
    const l2 = 
  "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXIvPbzLjaPLd8jgiv1TL/X8PXpJNgDkGRj9U9Lcx1yKURpQFVavcMkfWyO8r7JlZNMax0JKfLZUM1IePRjHlFw=="

    const l3 = "\n-----END PUBLIC KEY-----"

    const publicKey = l1 + l2 + l3

    const signature = "MEYCIQCPfWhpzxMqu3gZWflBm5V0aetgb2/S+SGyGcElaOjgdgIhALaD4lbxVwa8HUUBFOLz+CGvIioDkf9oihSnXHCqh8yV";

    console.log(verify.verify(publicKey, signature));// Prints: true or false

Answer 1

Here's how to inegrate with Nodejs.Crypto. First, the RSA private and public keys need to be generated. There are several ways to do that, here's an a way to do this online with encrypt.JS. You can use getSignatureByInput function below after private and public keys have been stored into the filesystem which generates a unique signature given a string input:

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

const getSignatureByInput = (input) => {
  let privatePem = fs.readFileSync('PRIVATE_KEY_FILE_PATH_GOES_HERE')
  let key = privatePem.toString('ascii')
  let sign = crypto.createSign('RSA-SHA256')
  sign.update(input)
  let signature = sign.sign(key, 'hex')

  return signature
}

Thereafter, to verify a signature, you can use the following function:

const getSignatureVerifyResult = (input) => {
        let signatureSignedByPrivateKey = getSignatureByInput(input)

        let pem = fs.readFileSync('PUBLIC_KEY_FILE_PATH_GOES_HERE')
        let publicKey = pem.toString('ascii')
        const verifier = crypto.createVerify('RSA-SHA256')

        verifier.update(input, 'ascii')

        const publicKeyBuf = new Buffer(publicKey, 'ascii')
        const signatureBuf = new Buffer(signatureSignedByPrivateKey, 'hex')
        const result = verifier.verify(publicKeyBuf, signatureBuf)

        return result;
}

getSignatureVerifyResult will return true/false depending on whether the signature are verified. Keep in mind that there's a plethora of algorithms to choose when it comes to signing.

Answer 2

Please see the fuller solution at this StackOverflow post which shows how to use the verify.update() and verify.verify() methods in node.js.