We’re rewarding the question askers & reputations are being recalculated! Read more.
141

Does it improve security to use obscure port numbers? If you're already using high entropy passwords or public key authentication, the answer is "not really". Mostly you're just getting rid of noise in logs. I worry about the unintended consequences of deviating from these recommendations. It depends on what port was picked. In Linux, by default all ...


81

ECDHE suites use elliptic curve diffie-hellman key exchange, where DHE suites use normal diffie-hellman. This exchange is signed with RSA, in the same way in both cases. The main advantage of ECDHE is that it is significantly faster than DHE. This blog article talks a bit about the performance of ECDHE vs. DHE in the context of SSL.


79

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 ...


73

Time is relative. Cryptography lives in the ethereal world of abstract computing machines: there are machines that can do operations. Bigger machines can do operations faster. There is no clock that you can enforce; physical time has no meaning. In other words, if an attacker wants to get your file earlier, he just has to buy a faster computer. Now one can ...


57

If you do not want to involve a third party, you (the party encrypting the file) could simply release the key to decrypt the file on the target date. I have seen this done for video game releases. Customers are allowed to download an encrypted copy of the game in advance. Then, when the release time comes, the game company simply releases the key. That way, ...


57

Yes, it does. The real question is: By how much? Why it does? You already have basic security, so the everyday bot attacks don't worry you. But there could be a 0-day tomorrow and the attackers know it won't be long until a patch is out, so they scramble to use it and won't bother with something complicated - they will just hit as many machines as possible ...


54

To add a bit of information on what @CodesInChaos says: When you use ECDHE instead of DHE, you may obtain the following advantages: Better performance. ECDHE is faster, for a given security level; @CodesInChaos points to an article which gives figures; see also this answer for why elliptic curve offer better performance. Smaller messages. An ECDH public ...


51

DTLS is currently (version 1.2) defined in RFC 6347 by explaining the differences with TLS 1.2 (RFC 5246). Most of the TLS elements are reused with only the smallest differences. The context is that the client and the server want to send each other a lot of data as "datagrams"; they really both want to send a long sequence of bytes, with a defined order, ...


50

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 ...


49

Carefully place a spaceship broadcasting the decryption key in orbit around a black hole. The pull of gravity will delay the message until the appropriate time. Or you could just do like normal people and place the key broadcasting spaceship an appropriate number of light years away from the intended audience.


36

There are a few confusions in your post. First of all, HMAC is not a hash function. More about HMAC later on. Hash Functions A hash function is a completely public algorithm (no key in that) which mashes bit together in a way which is truly infeasible to untangle: anybody can run the hash function on any data, but finding the data back from the hash output ...


32

Let me try to sum up what the landscape of end-to-end encrypted messaging protocols for group chat looks like: Protocols like PGP have been around for some time and offer "group messaging" by simply encrypting the content with a randomly generated symmetric key and then encrypting that key asymmetrically with the public keys of each of the recipients. These ...


30

No, it will not improve security. It may reduce log clutter, as automated attacks will only try default ports for e.g. ssh. But the port will still show up as SSH in a port scan, and shodan.io. Those automated attacks typically aim for low hanging fruit, with standard usernames such as root, smith and so forth, and weak passwords. If they succeed, you have ...


25

This book is a very good resource on wireless security. This section explains the details of the four-way handshake, but you really need to read the whole chapter to understand it. Both WPA2-PSK and WPA2-EAP result in a Pairwise Master Key (PMK) known to both the supplicant (client) and the authenticator (AP). (In PSK the PMK is derived directly from the ...


23

I see two conceptual paths for dealing with lag attacks: Punish lags. When an "artificial" lag is detected, evict the offender and enforce a ban period. This is hard to do in practice because there is a delicate balance to be found between people who cheat through lagging, and people who simply suffer from an occasional hiccup in their Internet connection. ...


21

Version fields occur in three places: as part of the header for each record that the client and the server send; as part of the ClientHello message from the client; as part of the ServerHello message from the server. Protocol Version Negotiation The version field in the ClientHello is the maximum version supported by the client implementation. For ...


21

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 ...


21

The problem here is not so much with CBC, but with alternatives that are easier to implement safely, without losing mathematical security.In fact, AES-CBC turned out to be notoriously difficult to implement correctly. I recall that older implementations of transport layer security don't have cryptographically secure initialization vectors, which are a must-...


20

Let's put the question the other way: What do you gain by disabling TLS 1.1? Security You and your quote seem to be implying that you want to move to TLS 1.2 because it's more secure than TLS 1.1. That's not really the case. TLS 1.2 did add new crypto, for example you can now use AES instead of 3DES, or ECDHE instead of DHE. At the moment, there are no ...


18

A non-standard port just means a service running on a port other than its default, usually as defined by the IANA port numbers registry. Running a service on a non-standard port doesn't really mean anything for security. It may reduce the amount of noise that a defender has to deal with in terms of automated scanning on the internet, where bots usually ...


17

This is incomplete. But hopefully of some use. https://wiki.imfreedom.org/wiki/IMessage and https://github.com/meeee/pushproxy (especially the docs section) have done some reverse engineering of apple's proprietary protocol. Seems that every apple device has a SSL/TLS client-side cert for authentication that setup to be known to apple's push server. This ...


17

Use secret sharing to split a private encryption key into N parts, parameterized to allow reconstruction of the key with K or more parts, where K <= N. Best done using CRM, as described on the following page: http://en.wikipedia.org/wiki/Secret_sharing Then send each part to independent services that agree to publish at a given date in the future. Up ...


17

Locked domains are domains which require additional hoops be leapt through in order to change ownership. The lock is requested by the owner of the domain and implemented by the registrar of the domain. Historically, transferring ownership of a domain required something like one of the authorized contacts faxing in a signed paper. And, believe it or not, ...


16

Details on Convergence are to be found in the Perspectives Project, notably the corresponding Usenix article. An attacker able to "hide" the server from all notaries (i.e. an attacker working over the local network of the server, mostly) is what the authors call the Lserver model. Ultimately, that attack "works" with default notaries, which use "network ...


15

The only reason to delay in saying goodbye is because of the potential impacts. In fact, the only reason to use any particular technology is that it does something for you and the cost/benefits are within your tolerances. If you have quantified the impacts of cutting off an older technology and you are ok with it, then there is no argument... I'm not sure ...


14

These are the golden rule of computer security: "It is impossible to hide anything from a competent user with system administrator privilege" and "any competent user with physical access to the device can always elevate himself to system administrator". You cannot hide any information from someone with physical control of the machine. If the secret you are ...


13

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 ...


13

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.


13

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 ...


Only top voted, non community-wiki answers of a minimum length are eligible