In fairness, there were choices, like in my case, I chose 1024 bit RSA instead of 2048 bit when I first setup the server knowing nothing about the consequences in the future. My assumption was that 1024 bit will be faster and secure enough so I choose.
I'm afraid you might have no choice in the future as newer clients/servers requires 2048 bit CA/encryption as minimum but for now you'll be fine not unless 1024 bit encryption is no longer safe.
IMO, using
1024-bit RSA encryption keys can be considered safe enough for now *
if* all you're protecting is access to the router's Admin WebGUI, primarily because that kind of VPN traffic is transient and limited to your own household. So unless you're a famous celebrity, corporate executive officer, political activist/dissident in an "unfriendly country," influential person in politics, economics, military, intelligence agent, etc., or someone that expects to be a target of nation-state sponsored cyberattacks/espionage, I would not worry about using 1024-bit RSA encryption with your home router's OpenVPN server, at least for now and for the near future (~2-4 years perhaps, depending on whose estimates you believe when such RSA key will be easily cracked as raw computing power increases).
However, if you're trying to protect more sensitive personally identifiable information (e.g. banking/financial/medical records, passport, driver's license, ID card, social security number, etc.), or perhaps some corporate proprietary info or intellectual properties that you have access to, then yes, the minimum recommendation is now 2048-bit encryption keys, with 4096-bit keys as ideal (and I likely would not be using an AIO ASUS home router).
Note that when using 1024-bit keys, there are a couple of options that you can use to make your OpenVPN traffic just a little bit more secure at the cost of some performance:
1) Set "
HMAC Authentication" option to at least "
SHA 256"
2) Set "
TLS control channel security" option to "
Encrypt channel"
This way, every TLS control channel packet is signed with an HMAC signature and encrypted, even during the initial multi-packet exchange/handshake that happens before client authentication is established.
The bottom line is that only you know what you're trying to protect & how valuable it is to you, so ultimately it comes down to a personal decision about how "secure" you want to make it.
Just my 2 cents.