Public Wi-Fi: What Encryption Covers Now, and What It Still Does Not

You are in an airport with one bar of signal and a network whose name is close to the airport’s name but not exactly it. Do you connect?

Two federal agencies give opposite answers, and both are in writing. The Federal Trade Commission’s consumer guidance says that because most websites now encrypt their traffic, “connecting through a public Wi-Fi network is usually safe.” The Cybersecurity and Infrastructure Security Agency has a page with a section heading that reads, in full, “Do not use public Wi-Fi networks.”

Both statements are honest. They are answers to different questions, and knowing which question you are asking is most of the decision. The FTC is describing the network layer after a decade of HTTPS. CISA’s prohibition is about transactions — banking, shopping, personal business. And the CISA page carrying that prohibition is now labeled by CISA itself as archived. Start there.

The prohibition is real, and it is dated

The page that says “do not use public Wi-Fi networks” carries this banner at the top, in CISA’s own words:

Archived Content. In an effort to keep CISA.gov current, the archive contains outdated information that may not reflect current policy or programs.

It was released February 1, 2021. CISA’s current advice on the same subject is narrower and entirely actionable. Its telework guidance answers “Is it safe to use public Wi-Fi?” this way:

Public Wi-Fi in airports, coffee shops, libraries, restaurants, malls, hotels and other public gathering spaces are not always secure. Before connecting to any public Wi-Fi, be sure to verify with the staff that the network name you are selecting is the legitimate network provided by the business, and that the communications over that hotspot are encrypted.

That is not a prohibition. It is a verification step. The difference between the two CISA pages is the difference between this article’s two questions, and the older page’s prohibition had a specific technical reason behind it.

What the old advice was protecting against

Read the FTC’s own guidance from February 2011 and the reason is explicit:

Most Wi-Fi hotspots don’t encrypt the information sent over the internet and are not secure. If a person uses an unsecured network to log in to an unencrypted site — or a site that uses encryption only on the sign-in page — other users on the network can see what is sent. New hacking tools — available for free online — make this easy, even for users with limited technical know-how.

The mechanics of that era are worth stating precisely, because they explain every piece of advice still circulating. When you logged in, the password field was usually encrypted. Everything after login was not. The server handed your browser a session cookie — the token that says “this is the logged-in user” — and that cookie traveled in the clear on every subsequent request. On an open network, anyone in radio range could copy it and replay it. They did not need your password. They did not need to understand encryption. They needed to be in the same room.

The FTC’s network test in 2011 followed from that: “A hotspot is secure only if it asks the user to provide a WPA (wifi protected access) password.” The FTC’s current guidance does not use that test. Its test is the padlock on the site — a different layer — and the shift between the two is the whole story of this article.

What changed

Two things, and they are both dated and checkable.

The web turned on encryption. In July 2018, with the release of Chrome 68, Chrome began marking all HTTP pages as “Not secure,” completing a rollout that started with password fields in Chrome 56 and data-entry pages in Chrome 62. That was the browser applying pressure, not the solution itself; the solution was that sites moved. The FTC’s current guidance can state as a premise what was not true in 2011: “Today, most websites do use encryption.”

The attack stopped being free. When the session cookie is carried inside TLS, there is nothing on the air to replay. The passive-sniffing attack that made the old advice necessary mostly fails against a modern HTTPS site.

The four layers, and which one you are buying

Layer	What it protects	What it does not
The Wi-Fi link (WPA2 or WPA3)	Your traffic from other devices on the same network	That the access point is the venue’s
TLS / HTTPS (the padlock)	The content between you and that website	That the website is honest, or that you reached the right one
DNS and metadata	Nothing	Which hosts you connect to, when, and how much
Network identity	Nothing, on an open or password-only network	Anything — unless the network uses WPA3 or enterprise authentication

Read the table as two separate questions. Is my traffic encrypted? and is this the network I think it is? The first one is largely solved. The second one is not solved, and it is where the real risk now lives.

Encryption is not authentication, and the standard says so

The clearest proof that those are two different things comes from the technology designed to make open networks safer.

Opportunistic Wireless Encryption — marketed by the Wi-Fi Alliance as Wi-Fi Enhanced Open, and specified in IETF RFC 8110 — encrypts the link on an open network without a password. The Wi-Fi Alliance’s announcement of the certification program on June 5, 2018 describes it as protecting “against passive eavesdropping without requiring a password or extra steps to join the network.” Its write-up of the technology adds the detail that matters most for anyone trying to make a decision at a gate:

It is expected that Enhanced Open networks will continue to be displayed without a “lock” icon in client devices.

So an open network may now be encrypted, and you will not be able to tell. The absence of a padlock on the Wi-Fi list is no longer evidence that the link is in the clear. More importantly, the Wi-Fi Alliance describes these networks, in its own press release, as unauthenticated: “These unauthenticated networks are often deployed in public locations such as local coffee shops and guest networks with a web portal in airports, hotels, and sports arenas.”

Encryption without authentication means: nobody else on the network can read your traffic, and anybody can be the network. That is the exact shape of the risk that remains, and it is what CISA’s instruction — “always confirm the name and password of a public Wi-Fi hotspot prior to use” — is aimed at.

The four risks encryption does not reach

1. A network you cannot verify. CISA calls this the evil twin: an attacker runs a hotspot with the venue’s name, and often a stronger signal, so your device prefers it. Your browser will show a padlock, because the site is legitimately encrypted; that padlock tells you nothing about the access point. Devices make this worse on their own. Phones and laptops remember network names and reconnect to them by default, so a network named after one your device already knows needs no interaction from you at all.

2. A site that is encrypted and dishonest. This is the FTC’s own warning, and it is the one most summaries leave out:

Scammers… also create fake websites and encrypt them to make you think they’re safe when they’re not. If you visit a scammer’s website, your data may be encrypted on its way to the site, but it won’t be safe from scammers operating the site.

A padlock proves privacy, not honesty. A captive portal — the page that asks you to accept terms or enter an email before granting access — is an unverifiable page you are being asked to type into, on a network you have not authenticated.

3. Your own device’s sharing settings. This is the one that has nothing to do with the network’s encryption and everything to do with yours:

An unsecured public wireless network combined with unsecured file sharing could allow a malicious user to access any directories and files you have unintentionally made available for sharing… Ensure that when you connect your devices to public networks, you deny sharing files and folders.

On Windows, that is the difference between the Private and Public network profiles: Microsoft describes the Public profile as the coffee-shop case, where “most of the other devices connected to it belong to strangers and you’d probably prefer they not be able to see or connect to your device,” and says Public “is the default profile for unidentified networks.” CISA’s instruction for that situation is the concrete one: deny sharing files and folders. Apple’s own security documentation contains a related admission about which networks it considers weaker: since iOS 18, the private Wi-Fi address feature has three modes, with the address rotating by default on “WPA, OWE, WEP, captive portals, and open networks,” and held fixed by default on WPA2 and WPA3 networks. The operating system is applying extra privacy protection precisely where it judges authentication to be absent.

4. Apps you cannot inspect. The FTC concedes that “it can be hard to tell if a mobile app uses encryption, but the majority do” — majority, not all. CISA is blunter, and its recommendation is the practical one: if you must use an unsecured network for something sensitive, use the company’s mobile website in a browser rather than its app, where you can at least check the address bar, or use cellular data instead.

One more residual, stated plainly: HTTPS hides the content, not the destination. The network operator can still see which hosts you connect to and when. That is not a reason to avoid a network; it is a reason not to assume a padlock makes you invisible.

WPA2’s one real flaw, and why it is closed

In October 2017, researchers disclosed the Key Reinstallation Attack — KRACK — against WPA2. CERT/CC’s advisory explains that the weakness was in the handshake protocol rather than in any vendor’s implementation, that an attacker had to be within wireless range to manipulate it, and that ten CVE identifiers were assigned to the vulnerabilities. The NSA’s follow-up advisory is unambiguous about the fix: “Install patches to both the clients and Access Systems as soon as they are made available.”

If your phone, laptop and the access point are current, KRACK is not your problem. WPA3, certified in June 2018, replaced the affected handshake with Simultaneous Authentication of Equals, requires Protected Management Frames, and adds a 192-bit suite for enterprise networks. WPA2 remains mandatory for certified devices and interoperates through a transitional mode, which is why a network can be perfectly fine on WPA2 today.

The VPN question, answered honestly

A VPN does one thing here: it moves your traffic inside an encrypted tunnel to a provider, so the venue can no longer see which hosts you connect to. That visibility does not disappear; it transfers to the VPN company.

What it does not do is encrypt anything you were not already encrypting. It does not stop you from joining a rogue access point, it does not make an encrypted scam site honest, it does not help with a portal that already harvested your login, and it does not make you anonymous. The FTC’s current public Wi-Fi guidance does not list a VPN among its recommendations — its list is passwords, two-factor authentication, current software and automatic updates.

The order of preference is therefore unglamorous. If the site you need is HTTPS and you confirmed the exact network name, use it. If the task is high-value and you have cellular signal, use cellular data instead — that removes the shared network from the question entirely rather than wrapping it in another party’s tunnel. A VPN belongs in the case where you need a specific network for a specific session and cannot verify it.

The decision, in one table

What you are doing	Open network, name unverified	Network name verified with staff	Cellular data
Reading, news, video	Fine	Fine	Fine
Signing in with two-factor authentication on	Prefer not to	Fine	Fine
Email, messaging, shopping with a stored card	Prefer cellular	Fine	Best
Banking, tax filing, work systems	Avoid	Acceptable; cellular is better	Best
Any site your browser marks “Not secure”	Do not	Do not	Do not
Installing a certificate or profile a portal asks for	Never	Never	Never

The last row is the one to keep. A captive portal has a legitimate need for an email address and no legitimate need for a certificate. If one asks you to install a profile, or to trust a new root certificate, that is the point at which you disconnect.

What this article will not tell you

It will not tell you to stop using public Wi-Fi, because that advice has a date on it and the date has passed — but it also will not tell you the network is harmless. The honest position is narrower than either: the transport is mostly solved, the identity of the network is not, and the second problem has a one-step check.

It will also not tell you that the site’s own HTTPS is enough, because the FTC’s own page says it is not: encryption on the way to a dishonest site does not make the site honest. And it will not give you a rule that survives every case. The pattern worth carrying forward is that most public-Wi-Fi advice you encounter was written for a web that no longer exists, and the way to tell the difference is to ask which layer the advice is about.

Byte is the technology site of the Omni Mundi Compendium network. The account-side answer, for when a password does leak, is in Which Two-Factor Method to Use and The First 72 Hours After a Data Breach Notice; the tools for a leaked identifier are compared in Credit Freeze, Fraud Alert, or Credit Lock; and the legal layer that covers the rest is in What US Privacy Law Actually Protects.

This article is general information about network security, not professional security advice for a specific network or organization, and it describes vendor and standards-body features as published rather than as implemented in any particular device. Menu names, defaults and supported protocols vary by operating system version, device and access point, and change over time. CISA’s pages quoted here are reproduced as published, including the archived page’s own warning that it may not reflect current policy. It is AI-written and independently AI-reviewed before publication; the review standard and this article’s findings are recorded in the network’s editorial review log.