Why not use HTTPS for everything?

问题:

If I was setting up a server, and had the SSL certificate(s), why wouldn't I use HTTPS for the entire site instead of just for purchases/logins? I would think it would make more sense just to encrypt the entire site, and protect the user entirely. It would prevent problems such as deciding what has to be secured because everything would be, and it's not really an inconvenience to the user.

If I was already using an HTTPS for part of the site, why wouldn't I want to use it for the entire site?

This is a related question: Why is https only used for login?, but the answers are not satisfactory. The answers assume you've not been able to apply https to the entire site.

回答1:

I can think of a couple reasons.

• Some browsers may not support SSL.
• SSL may decrease performance somewhat. If users are downloading large, public files, there may be a system burden to encrypt these each time.

回答2:

In addition to the other reasons (especially performance related) you can only host a single domain per IP address* when using HTTPS.

A single server can support multiple domains in HTTP because the Server HTTP header lets the server know which domain to respond with.

With HTTPS, the server must offer its certificate to the client during the initial TLS handshake (which is before HTTP starts). This means that the Server header hasn't been sent yet so there is no way for the server to know which domain is being requested and which certificate (www.foo.com, or www.bar.com) to respond with.

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*Footnote: Technically, you can host multiple domains if you host them on different ports, but that is generally not an option. You can also host multiple domains if your SSL certificate is has a wild-card. For example, you could host both foo.example.com and bar.example.com with the certificate * .example.com

回答3:

SSL/TLS isn't used nearly often enough. HTTPS must be used for the entire session, at no point can a Session ID be sent over HTTP. If you are only useing https for logging in then you are in clear violation of The OWASP top 10 for 2010 "A3: Broken Authentication and Session Management".

回答4:

The biggest reason, beyond system load, is that it breaks name-based virtual hosting. With SSL, it's one site - one IP address. This is pretty expensive, as well as harder to administer.

回答5:

Why not send every snail-mail post in a tamper-proof opaque envelope by Registered Mail? Someone from the Post Office would always have personal custody of it, so you could be pretty sure that no one is snooping on your mail. Obviously, the answer is that while some mail is worth the expense, most mail isn't. I don't care if anyone reads my "Glad you got out of jail!" postcard to Uncle Joe.

Encryption isn't free, and it doesn't always help.

If a session (such as shopping, banking, etc.) is going to wind up using HTTPS, there's no good reason not to make the whole session HTTPS as early as possible.

My opinion is that HTTPS should be used only when unavoidably necessary, either because the request or the response needs to be safeguarded from intermediate snooping. As an example, go look at the Yahoo! homepage. Even though you're logged in, most of your interaction will be over HTTP. You authenticate over HTTPS and get cookies that prove your identity, so you don't need HTTPS to read news stories.

回答6:

For high latency links the initial TLS handshake requires additional round trips to validate the certificate chain (including sending any intermediate certificates), agree on cipher suites and establish a session. Once a session is established subsequent requests may utilize session caching to reduce the number of round trips but even in this best case there is still more round trips than a normal HTTP connection requires. Even if encryption operations were free round trips are not and can be quite noticable over slower network links especially if the site does not leverage http pipelining. For broadband users within a well connected segment of the network this is not an issue. If you do business internationally requring https can easily cause noticable delays.

There are additional considerations such as server maintenance of session state requiring potentially significantly more memory and of course data encryption operations. Any small sites practically need not worry about either given server capability vs cost of todays hardware. Any large site would easily be able to afford CPU /w AES offload or add-on cards to provide similar functionality.

All of these issues are becoming more and more of a non-issue as time marches on and the capabilities of hardware and the network improve. In most cases I doubt there is any tangable difference today.

There may be operational considerations such as administrative restrictions on https traffic (think intermediate content filters..et al) possibly some corporate or governmental regulations. Some corporate environment require data decryption at the perimeter to prevent information leakage ... interference with hotspot and similiar web based access systems not capable of injecting messages in https transactions. At the end of the day in my view reasons for not going https by default are likely to be quite small.

回答7:

https is more resource-hungry than the normal http.

It demands more from both the servers and the clients.

回答8:

If whole session is encrypted then you won't be able to use caching for static resources like images and js on proxy level eg ISP.

回答9:

You should use HTTPS everywhere, but you will lose the following:

1. You should definitely not use SSL Compression or HTTP Compression over SSL, due to BREACH and CRIME attacks. So no compression if your response contains session or csrf identifiers. You can mitigate this by putting your static resources (images, js, css) on a cookie-less domain, and use compression there. You can also use HTML minification.

2. One SSL cert, one IP address, unless using SNI, which doesn't work on all browsers (old android, blackberry 6, etc).

3. You shouldn't host any external content on your pages that don't come over SSL.

4. You lose the outbound HTTP Referer header when browser goes to an HTTP page, which may or may not be a problem for you.

回答10:

Well, the obvious reason is performance: all of the data will have to be encrypted by the server before transmission and then decrypted by the client upon receipt, which is a waste of time if there's no sensitive data. It may also affect how much of your site is cached.

It's also potentially confusing for end users if all the addresses use https:// rather than the familiar http://. Also, see this answer:

Why not always use https when including a js file?

回答11:

https requires the server to encrypt and decrypt client requests and responses. The performance impact will add up if the server is serving lots of clients. That's why most current implementations of https is limited to password authentication only. But with increasing computing power this may change, after all Gmail is using SSL for the entire site.

回答12:

In addition to WhirlWind's response, you should consider the cost and applicability of SSL certificates, access issues (it's possible, though unlikely, that a client may not be able to communicate via the SSL port), etc.

Using SSL isn't a guaranteed blanket of security. This type of protection needs to be built into the architecture of the application, rather than trying to rely on some magic bullet.

回答13:

I was told that on one project at our company, they found that the bandwidth taken up by SSL messages was significantly more than for plain messages. I believe someone told me it was an astounding 12 times as much data. I have not verified this myself and it sounds very high, but if there is some sort of header added to each page and most pages have a small amount of content, that may not be so far out.

That said, the hassle of going back and forth between http and https and keeping track of which pages are which seems like too much effort to me. I only once tried to build a site that mixed them and we ended up abandoning the plan when we got tripped up by complex things like pop-up windows created by Javascript getting the wrong protocol attached to them and that sort of thing. We ended up just making the whole site https as less trouble. I guess in simple cases where you just have a login screen and a payment screen that need to be protected and they're simple pages, it wouldn't be a big deal to mix-and-match.

I wouldn't worry much about the burden on the client to decrypt. Normally the client is going to be spending a lot more time waiting for data to come over the wire than it takes to process it. Until users routinely have gigabit/sec internet connections, client processing power is probably pretty irrelevant. The CPU power requried by the server to encrypt pages is a different issue. There might well be issues of it not being able to keep up with hundreds or thousands of users.

回答14:

One other small point (maybe someone can verify), If a user types data into a form item such as a text box and then for some reason refreshes the page or the server crashes out for a second, the data the user entered is lost using HTTPS but is preserved using HTTP.

Note: I'm not sure if this is browser specific but it certainly happens with my Firefox browser.

回答15:

windows Server 2012 with IIS 8.0 now offers SNI which is Server Name Indication which allows multiple SSL Web Applications in IIS to be hosted on one IP Address.

回答16:

The HTTPS is HTTP that is secured with SSL. You may need to register a paid certificate to make your site maintain and trust.

HTTPS is needed when your site needs to exchange information with the user and you want to keep information secured by encryption.

If not, HTTPS is not necessary but you still can use it if you want.