securecookies

[komuw]

• https://github.com/gorilla/securecookie

[komuw]

There's a version2 here: https://github.com/gorilla/securecookie/tree/elithrar/v2 (see: gorilla/securecookie#43 (comment))

[komuw]

https://gist.github.com/komuw/4d44a25e1b6786100ffe0308106e80f2

[komuw]

https://github.com/gorilla/securecookie/blob/f37875ef1fb538320ab97fc6c9927d94c280ed5b/securecookie.go#L247-L293

[komuw]

package main

import (
	"fmt"
	"net/http"
	"time"

	"github.com/komuw/ong/cookie"
	"github.com/komuw/ong/enc"
)

func someHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		key := "hard-passwd"
		e := enc.New(key)

		cookieName := "logID"
		cookieVal := "slkPPjadm"
		encryptedEncodedCookieVal := e.EncryptEncode(cookieVal)

		cookie.Set(
			w,
			cookieName,
			encryptedEncodedCookieVal,
			"example.com",
			15*time.Minute,
			false,
		)

		fmt.Fprint(w, "hello")
	}
}

[komuw]

https://www.alexedwards.net/blog/working-with-cookies-in-go

• Effectively, encrypting our cookie data using AES-GCM is a relatively easy way to give us confidential, tamper-proof, cookies in a single step.

• You can use hmac to make sure cookies are tamper proof

• Or you can use an authenticated encryption to achieve encryption and tamper proofing

• Cookies can be edited by clients and hence the server should never trust them.
  You can however verify(on the server) if a cookie has been edited. One way is to generate a HMAC signature of the cookie name and value, and then prepend this signature to the cookie value before sending it to the client.
  This is tamper proofing(or message authentication)

• Hmac signed cookies can be read/seen by the client but cannot be changed(or rather, any change would be caught on the server).
  There are times when we would not want our cookies to be seen by clients. We can use encryption for that; when clients read, they get gibberish.
  Using a cipher.AEAD can achieve both encryption & tamper-proofing.

[komuw]

Note, you should encrypt both the name and value together, and store the result as the cookie value.
This is because enc.New uses cipher.AEAD which provides encryption and authentication.
We also want to authenticate(ie, ensure it has not been tampered with) the cookie name.

func someHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		key := "hard-passwd"
		e := enc.New(key)

		cookieName := "logID"
		cookieVal := "slkPPjadm"
		encryptedEncodedCookie := e.EncryptEncode(fmt.Sprintf("%s:%s", cookieName, cookieVal))

		cookie.Set(
			w,
			cookieName,
			encryptedEncodedCookie,
			"example.com",
			15*time.Minute,
			false,
		)

		fmt.Fprint(w, "hello")
	}
}