Some questions about network/transmission security

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thelonesoldier
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Some questions about network/transmission security

Postby thelonesoldier » Mon Oct 01, 2012 1:51 am UTC

Hi all, I had some questions about network/internet/etc security/encryption/moreslashes and I am always impressed with the insane amount of collective knowledge I see on the fora here so I thought it might be a good place to ask. I've tried doing my own research but I feel like I only half-understand.

First, I've gotten the impression from what I've read that SSL and TSL provide secure data transfer even over an unsecured network (free Wifi at McDonalds or whatever); is that correct? If I understand right (and I wouldn't be surprised if I didn't) the user's computer and the web server use public key encryption to exchange a single-session symmetric key which is used for the remainder of data transfer. Is that still secure over a public network? I guess I don't understand why someone sniffing the connection couldn't intercept the initial key exchange that starts the secure connection and thus be able to decrypt all of it, which is probably from my not fully grasping the mechanics of the system.

Secondly, does a secured Wifi network provide any protection against sniffing by other users who are also connected? I assume if everyone connects with the same key (for example with a typical home wireless router) anyone on the connection can sniff anyone else who is, but those without the key can't?

Thirdly, at my university, there is campus-wide secured Wifi network. Each student has his or her own username and password to connect to the secure network - should that mean each student is secure from sniffing by other students, or is it probably just an easier way to provide a secured network without giving the students a single key that they'd probably post online anyway?

Thanks for any explanations!

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WanderingLinguist
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Re: Some questions about network/transmission security

Postby WanderingLinguist » Mon Oct 01, 2012 1:15 pm UTC

thelonesoldier wrote:First, I've gotten the impression from what I've read that SSL and TSL provide secure data transfer even over an unsecured network (free Wifi at McDonalds or whatever); is that correct?

Yes, that's correct.
thelonesoldier wrote: If I understand right (and I wouldn't be surprised if I didn't) the user's computer and the web server use public key encryption to exchange a single-session symmetric key which is used for the remainder of data transfer. Is that still secure over a public network?

Yes, it's still secure.
thelonesoldier wrote:I guess I don't understand why someone sniffing the connection couldn't intercept the initial key exchange that starts the secure connection and thus be able to decrypt all of it, which is probably from my not fully grasping the mechanics of the system.

They can intercept the symmetric key, sure, but it won't do them any good because it's encrypted with the asymmetric key. Basically, the initial exchange (where the symmetric key is established) is done using public key encryption. In public key encryption, each party sends their public key to the other party. You can encrypt with the public key, but only decrypt with the matching private key (which was never shared). My understanding is that this could be used for the whole session, but it's a bit slower, so the public key encryption method is used to establish the symmetric key that's actually used for the rest of the session.

thelonesoldier wrote:wifi stuff

I'm not an expert on wi-fi, but my understanding is that unencrypted wi-fi is pretty much open to sniffing by anyone. However, encrypted wi-fi, even with a known password, is still quite hard to sniff. But I could be wrong. It also depends on what wi-fi encryption system your using. Some of them are insanely easy to break, some are quite hard. For example, don't use WEP -- it's incredibly easy to hack a WEP network.

As for your school's user/password login system for wi-fi: It's my understanding that wi-fi networks do not accept a username and password for log-in. They only take a key. If it's asking you for a username and password, that's something separate (possibly a router that's redirecting you to a login page if you're not logged in). So my guess is that your school has a separate layer of security. However, if they don't also have a key for the wi-fi network as well, then even with the log-in, your data may still be open to sniffing.

Hope this helps!

AgentME
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Re: Some questions about network/transmission security

Postby AgentME » Mon Oct 08, 2012 5:10 am UTC

Several wifi encryption schemes allow a username and password to be used to authenticate yourself.

However, many of them use MSCHAPv2, which has recently been shown as broken, so for about $20 someone can rent computing time on a specialized DES-cracking machine to crack a MSCHAPv2-"secured" session.

Meem1029
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Re: Some questions about network/transmission security

Postby Meem1029 » Mon Oct 08, 2012 2:35 pm UTC

Oh lovely. And here I was assuming that the system my university used would be secure. Looks like I was wrong...
cjmcjmcjmcjm wrote:If it can't be done in an 80x24 terminal, it's not worth doing

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WanderingLinguist
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Re: Some questions about network/transmission security

Postby WanderingLinguist » Mon Oct 08, 2012 9:47 pm UTC

Always best to use additional security over a wi-fi connection. Most major services like Gmail, Facebook, etc., will redirect you to an "https" version of the page (which is encrypted), but always best to check that the URL really is an https one, rather than http, if you care about security.

Carnildo
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Re: Some questions about network/transmission security

Postby Carnildo » Tue Oct 09, 2012 3:25 am UTC

WanderingLinguist wrote:They can intercept the symmetric key, sure, but it won't do them any good because it's encrypted with the asymmetric key. Basically, the initial exchange (where the symmetric key is established) is done using public key encryption. In public key encryption, each party sends their public key to the other party. You can encrypt with the public key, but only decrypt with the matching private key (which was never shared). My understanding is that this could be used for the whole session, but it's a bit slower, so the public key encryption method is used to establish the symmetric key that's actually used for the rest of the session.

"A bit slower" is something of an understatement. Public-key encryption is typically thousands of times slower than symmetric-key encryption: not a problem if you're encrypting something small like a symmetric encryption key, but rather problematic for a multi-megabyte image.


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