There are some attacks you are vulnerable to on public WiFi that a VPN can help with.
More generally, whoever is transporting your data knows who you are talking to. If you don’t use a VPN, your ISP and whoever owns the router know what websites you are visiting (although they don’t know the specific content). If you use a VPN, your ISP and router know you are using that VPN, but not what websites you are visiting. Now your VPN knows what websites you are visiting, but they still don’t know what the content is.
You can substitute “Tor” for “VPN” in the above and be largely correct. Tor acts like a VPN, but every packet goes through multiple hops, so an attacker would need to do quite a bit of work (i.e. compromise multiple nodes) to link traffic to you.
So:
TLS (https) - network owner can’t see specific content, but can determine what sites you visit
VPN - network owner can’t tell what sites you visit, but can tell you’re on a VPN; VPN can tell what sites you visit, but not specific content
Tor - network owner can’t tell what sites you visit, but can tell you’re using Tor; Tor exit node operators can see what sites people using it visit, but can’t attribute it to an individual user w/o a sophisticated attack
In most cases, TLS is perfectly fine, provided you make sure to not click through any TLS errors (i.e. certificate can’t be validate => probable middle-man attack), and using a VPN is probably overkill. A VPN protects you from that middle-man attack, but honestly, if you’re savvy enough to use a VPN, you’re probably savvy enough to not get compromised by a middle-man attack. Likewise if you use Tor, you’re probably savvy enough to not get compromised by a middle-man attack.
That said, I fully support using Tor and VPNs, I just won’t go so far as to say someone is dumb for not using them on public Wi-Fi. Make sure you’re connecting to a real Wi-Fi service and don’t disable TLS protections and you’re probably fine, from a security perspective. If you’re likely to be targeted by a government agency, Tor is the bare minimum of what you should use.
There are some attacks you are vulnerable to on public WiFi that a VPN can help with.
More generally, whoever is transporting your data knows who you are talking to. If you don’t use a VPN, your ISP and whoever owns the router know what websites you are visiting (although they don’t know the specific content). If you use a VPN, your ISP and router know you are using that VPN, but not what websites you are visiting. Now your VPN knows what websites you are visiting, but they still don’t know what the content is.
I hope that helps.
What about DoH/DoT which comes enabled by default in some browsers I believe? This should “hide” your activity from isp/router as well, shouldn’t it?
What about using tor instead of a vpn?
You can substitute “Tor” for “VPN” in the above and be largely correct. Tor acts like a VPN, but every packet goes through multiple hops, so an attacker would need to do quite a bit of work (i.e. compromise multiple nodes) to link traffic to you.
So:
In most cases, TLS is perfectly fine, provided you make sure to not click through any TLS errors (i.e. certificate can’t be validate => probable middle-man attack), and using a VPN is probably overkill. A VPN protects you from that middle-man attack, but honestly, if you’re savvy enough to use a VPN, you’re probably savvy enough to not get compromised by a middle-man attack. Likewise if you use Tor, you’re probably savvy enough to not get compromised by a middle-man attack.
That said, I fully support using Tor and VPNs, I just won’t go so far as to say someone is dumb for not using them on public Wi-Fi. Make sure you’re connecting to a real Wi-Fi service and don’t disable TLS protections and you’re probably fine, from a security perspective. If you’re likely to be targeted by a government agency, Tor is the bare minimum of what you should use.