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69

You should think of OSI layers as packaging. Let's say I want to ship a glass to you. I chose an original package for advertisement purposes, showing how nice is my product and what you can buy to add to your "glass" experience. That's the high layer of my protocol. Then I put this package in a box filled with soft thingies because I don't want it to be ...


48

Is Git crowdsourcing the production of SHA-1 preimages? Not to any meaningful degree. Github doesn't say how many commits it's tracking, but it's probably not more than a few billion. For comparison, there are 1,461,501,637,330,902,918,203,684,832,716,283,019,655,932,542,976 possible SHA-1 hashes, so the odds of finding a plaintext matching an arbitrary ...


20

This behaviour is specified by RFC2617. The reason for the extra round trip is that the server can request different kinds of authentication: basic, digest, etc. If you know in advance that the server takes basic authentication, then as you say, you can save a round trip. But that isn't the default, and I think the .NET libraries are right to expose this as ...


12

There have been some discussions about mitigating issues with some record splitting. Namely, what makes Poodle efficient is that padding may use up to a full block (8 bytes with 3DES or RC2, 16 bytes with AES). When this happens, only the last byte of the block is checked by the recipient, which is why the alteration from the attacker gets through with ...


12

You could probably compute your own SHA1 hashes quicker from small arbitrary texts than that you harvest the hashes that someone else computed. But there's a lot of possible SHA1 digests, about as many as atoms in the world. That illustrates the challenge if you want to keep a list of all known digests and search that list.


11

Competition is a good thing, and so is redundancy/diversity. While Heartbleed affected a lot of systems and services due to how widespread OpenSSL is, it certainly didn't effect 100% of systems. Having redundancy in software in general is good, if you have a problem with one piece of software you can fail over to another or mitigate the risk by spreading ...


11

To complement the answer from @raz, one must be aware of Protocol Downgrade Attacks. Browsers like IE send their maximum supported version, and then the server chooses (in your case, IE says "I know up to TLS 1.2" and the server responds with "we will do TLS 1.0"). However, browsers know that there exist buggy servers out there, that will simply have an ...


11

What you have defined is not security. SSL can give you security. So...your question is easy to answer: Yes - SSL is up to 100% more secure than encoding. While elements of your 2nd paragraph have some basis in fact (there are malicious MITM attacks etc) they can be protected against, whereas your solution has no protection, and is easily decoded by ...


10

The server chooses which cipher suite to use for establishing the secure channel. The client (browser) poses the protocols and encryption algorithms that it will accept. The server chooses the one it deems most secure (based on its own list of acceptable protocols) and that is used for the secure channel. If the server does not see any cipher suites that ...


10

While OSI is just a model, and in reality the layers can be blurred or nonexistent, the concept of layering protocols is specifically to allow a change in a particular layer to leave the layers above and below it alone. As an example: Physical - does a basic packet care whether it is travelling over copper, fibre or wireless? It could travel over all ...


9

SSLv3 protocol is flawed. This cannot be fixed. Generally, an attacker would exploit this by forcing the victim to connect to a server using SSLv3 by forcing connections using higher protocols to fail. TLS_FALLBACK_SCSV attempts to stop the browser/server from falling all the way back to SSLv3 if a higher protocol has already been tried. As you can ...


8

This question can be easily extended to any problem which can be solved by a library, security-related or not. This answer applies to libraries which implement any standardized functionality and isn't specific to SSL. License incompatibility Not all software licenses are compatible with each other. When you want to use a GPL-licensed library, you need to ...


8

The amount of human effort which has gone into computing each of those SHA-1 hashes found in Git is significant. And that means the number of hashes computed that way is fairly limited. If you want to find collisions, you need zero human effort per hash and very little computer time spend on each hash. Bitcoin might be the only system with enough computing ...


5

By definition, if it doesn't matter if someone has access to or modifies your data, then it isn't sensitive and doesn't have to be secure. For things that have to be secure, then it is ill advised to use a custom protocol unless you can invest the huge amounts of time and resources necessary to ensure its security (millions). Note that there is also a ...


5

SSL 2.0 is not a vulnerability; it is a protocol which happens to contain structural vulnerabilities, and, as such, should not be allowed. There is a RFC which says just that, and lists the main known deficiencies in SSL 2.0: SSL version 2.0 [SSL2] deficiencies include the following: o Message authentication uses MD5 [MD5]. Most security-aware users ...


4

You have to make a distinction between the applicative protocol and the transport protocol. SSL/TLS is a transport protocol: it ensures some security-related guarantees (confidentiality, integrity, some authentication) for a a bidirectional stream of bytes. What these bytes mean is what the "applicative protocol" defines. E.g. in HTTPS, HTTP is the ...


4

It took nearly a year, but NIST has released this bulletin explaining the update and also providing the updated document for SP 800-52 Revision 1. The answer to your question is expressed in the bulletin: NIST published the original version of SP 800-52 in 2005, but withdrew it in March 2013 because the guideline had not yet been updated based on ...


4

I am assuming you are making a toy protocol for the fun of it -- learn about crypto, have fun implementing something, but understand that this toy scheme is probably flawed and that if you have sensitive data you should use well-known vetted protocols, not toy schemes you just came up with. (If not see reasons to not roll your own ). First, RSA just ...


4

I suspect you answered your own question already. The mere fact that you want to protect the data implies that it is sensitive and should not be modified or leaked. If this is not the case, why bother with protecting at all? If the opposite is true (the data should be protected) then the "rule" stands that the use of custom protocols and encryption ...


3

If everyone has a complete copy of the game state at time T, and the permitted moves can be deduced strictly from knowing the game state, then it's possible to identify cheating without an arbitrator, though telling who is cheating requires that the majority of players are honest. Everyone starts the game with a complete copy of the game state (implicit in ...


3

The password in SRP is actually a shared secret of (possibly) low entropy. It can be the "password" as the human user understands it, or anything that is deterministically derived from the password. In your case, yes, using a password hashing function such as PBKDF2 is a valid approach. It has the following caveats: PBKDF2, like bcrypt and other good ...


3

DoS attacks don't require any open ports on your side. They can just use all your bandwidth even if the ports are closed. How? The IP packet are sent from the attacker, and routed through several routers until it reaches your system. If the port is open, the connection succeeds. If not, your system can send back a "Port closed" message or simply drop the ...


3

As usual, the problem is one of definition. Namely, what makes the device 'D' more "genuine" than a PC run by some ill-intentioned individual ? If you get down to it, you will say something like: device D is genuine because that's the true piece of tangible hardware, the accumulation of atoms which came out from the factory. This is fine as far as definition ...


3

TCP provides to applications a stream interface. There are a few exceptions where the details leak through, but generally a TCP socket is opened, and then each side sends a series of bytes to the other. Those bytes will be delivered intact and in order, up until the point where the remote end closes the connection (which you will be informed of). ...


2

If you store a key, password, etc. in the source code you will never be able to reasonably expect to keep it secret unless you also control the system. What you are describing would only be obscurity, obfuscation, or data hiding. If you want only the program to be able to decrypt, its sounds like a case for using asymmetric cryptography. You may have a ...


2

The connections CrashPlan uses are encrypted using TLS. (I've casually seen the traffic when looking at other things.) As for whether or not it's safe: the protocol doesn't really matter, only whether CrashPlan has exploitable bugs in their software, and that's pretty hard to discern without either extensive reverse engineering or access to their source ...


2

There is no proof that the message was intended for B. So, intruder I can intercept the message signed by A and redirect it to B, authenticating I as A. But what is a harmful attack? For example in a bank-client interaction scenario? If I understand you correctly, you've just described the first part of a Man In The Middle (MITM) attack.


2

A MAC address is unsuitable for this for several reasons: The MAC address can be changed freely by the user in software, and will change if the network hardware is replaced. A wireless device broadcasts its address to everyone around, so it's hardly a secret. MAC addresses are supposed to be unique, but in practice, they aren't. A device with multiple ...


2

Sending one type of network traffic over another protocol is called network tunneling or covert channeling. This is quite easy to do, and with some experience, you can send plaintext data over port 443 (to make it appear encrypted to the untrained eye) or send IM messaging traffic over port 80...the opportunities are endless. The method of sending data ...


2

If a port on the target machine is closed, it will either respond that the connection was refused or it will drop the packet silently. Ports being closed or "stealth" will not stop a DoS as the target will receive the packets whether it responds or not. In some cases ports are entirely irrelevant (see ping flood, smurf attack).



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