verifing WebPush JWT on node.js

verifyJWTSign.js

"use strict"
const util=require('util')
const jwt=require('jsonwebtoken')
const asn = require('asn1.js');
// const fs = require('fs')

// ECDSA public key ASN.1 format
const ECPublicKey = asn.define("PublicKey", function() {
	this.seq().obj(
		this.key("algorithm").seq().obj(
			this.key("id").objid(),
			this.key("curve").objid()
		),
		this.key("pub").bitstr()
  );
});

// convert public key from p256ecdsa to PEM
function getPemFromPublicKey(public_key){
	return ECPublicKey.encode({
		algorithm: {
			id: [1, 2, 840, 10045, 2, 1],  // :id-ecPublicKey
			curve: [1,2,840,10045,3,1,7] // prime256v1
		},
		pub: {
			// このunused により bitstringの先頭に 00 が置かれる。
			// 先頭の00 04 が uncompressed を示す
			// https://tools.ietf.org/html/rfc5480#section-2.3.2
			// http://www.secg.org/sec1-v2.pdf section 2.3.3
			unused: 0, 
			data: public_key,
		},
	}, "pem", {label: "PUBLIC KEY"})
}

function decodeBase64(src){
    return new Buffer(src,'base64')
}

// test data
const auth_header = "WebPush eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.eyJhdWQiOiJodHRwczovL21hc3RvZG9uLW1zZy5qdWdnbGVyLmpwIiwiZXhwIjoxNTI2NTU5OTg2LCJzdWIiOiJtYWlsdG86dGF0ZWlzdUBnbWFpbC5jb20ifQ.h8p58F3MmbXUSQKyxoQSWG8Qu8EJoJqykbnPXuOcyeImlfe4uHKhpUYrK-mPH5lx_Adoz_t522UHYSqadgPHRA"
const crypto_key = "dh=BBjDnasYpkCkA1EmvOGO0AhH_CDlMrv1Os0SLH9ynjuPxeZ6XVbC-RZSyEv_T14FA2zs3YnWqKFnX8XpbyLQRPg;p256ecdsa=BLzIgsz-VRhTxuVgNoQljTwAFzxbanfGxNk8tldaruBztvsK9elES_2lE_8c91-RNOInEBEFUrCzDw-60bzUCr8"

const reAuthorizationWebPush = new RegExp("^WebPush\\s+(\\S+)")
const reCryptoKeySignPublicKey = new RegExp("p256ecdsa=([^;\\s]+)")

let m = reAuthorizationWebPush.exec( auth_header )
if( !m ){
	console.log("header not match: Authorization")
}else{
	const token = m[1]

	m = reCryptoKeySignPublicKey.exec(crypto_key)
    if( !m ){
		console.log("header not match: Crypto-Key")
	}else{
		const public_key = decodeBase64(m[1])
		const pem = getPemFromPublicKey(public_key)
	    // fs.writeFileSync("./public2.pem", pem + "\n");

		const decoded = jwt.verify(token, Buffer.from(pem), { algorithms: ['ES256'] })
		console.log(decoded)
    // { aud: 'https://mastodon-msg.juggler.jp',exp: 1526559986,sub: 'mailto:tateisu@gmail.com' }
    
		// error case
		try{
			const decoded2 = jwt.verify(token+"xxx", Buffer.from(pem), { algorithms: ['ES256'] })
		}catch(err){
			console.log(`verify failed: ${err}`)
      // verify failed: JsonWebTokenError: invalid token
		}
	}
}


/*

JWTトークンの署名の検証

(1) openSSLで作成したPEMファイルで署名の作成と検証
(2) 公開鍵をp256ecdsaバイトデータからPEMフォーマットに変換

// jsonwebtoken はPEMファイルがあればjwtのエンコードとデコード(署名検証)ができる
// openssl ecparam -genkey -name prime256v1 -noout -out private.pem
// openssl ec -in private.pem -pubout -out public.pem
var priv = fs.readFileSync('./private.pem')
var token = jwt.sign("{ foo: 'bar' }", priv, { algorithm: 'ES256' })
console.log(token)
var pub = fs.readFileSync('./public.pem')
var decoded = jwt.verify(token, pub, { algorithms: ['ES256'] })
console.log(decoded)

dump of pem file
$ openssl asn1parse -in public.pem -dump
    0:d=0  hl=2 l=  89 cons: SEQUENCE          
    2:d=1  hl=2 l=  19 cons: SEQUENCE          
    4:d=2  hl=2 l=   7 prim: OBJECT            :id-ecPublicKey
   13:d=2  hl=2 l=   8 prim: OBJECT            :prime256v1
   23:d=1  hl=2 l=  66 prim: BIT STRING        
      0000 - 00 04 e0 a5 f8 06 b7 0a-05 cc fa 97 06 cb f8 04   ................
      0010 - 0c 1b e3 52 13 3d bb a9-de 74 7d 25 ac 7b 39 d0   ...R.=...t}%.{9.
      0020 - e1 e6 ee 3a 96 47 9f be-41 ae c2 ff d0 36 53 43   ...:.G..A....6SC
      0030 - 88 e6 5d f7 a4 09 32 13-d6 57 e5 91 3f 5d d6 70   ..]...2..W..?].p
      0040 - 07 c2     

d:depth 
hl:header length (tag and length octets) of the current type.
l: length of the contents octets.

*/