Wikipedia:Reference desk/Archives/Computing/2014 November 28

= November 28 =

Two broadband connections for greater bandwidth?
I am in the UK living a couple of miles from the nearest town. Our broadband runs at 3 Mb/s generally (but can be slower) and this is causing distress in the family as my two boys move through their teenage years. Our usage is 100 - 200 GByte per month and we are on ADSL2+. Our telephone exchange and cabinet have recently been upgraded to fibre but our ISP estimates show a predicted speed of 2.4 Mb/s if we went to FTTC (the estimate is 2.0  Mb/s for our current setup). British Telecom themselves estimate "2Mb - 5Mb" for "Unlimited Faster Broadband". I have spoken to an advisor at our ISP who seems knowledgable and who says a fibre contract will not help us because of the distance our telephone wire (an overhead wire on poles) has to run to the nearest cabinet where the fibre starts. He said the only solution would be to get a second telephone connection which would roughly double our costs from £30 to £60 per month. Are there any other realistic solutions? If we had two telephone connections would we still be served down a single length of wire and so suffer from contention? I have found WP:Reference_desk/Archives/Computing/2011_May_9 and an interesting web page which leave me uncertain. Thincat (talk) 10:05, 28 November 2014 (UTC)


 * I live more than six miles from the exchange, and so get only 1 Mb/s from BT. We have a microwave sytem that is a bit faster, but the only way to get the speeds that you will require in the future is to have fibre direct to your house.  You could ask BT about this, but they seem very reluctant to install it, and charge a much higher monthly fee if they do agree.  Are you within sight of a friend who lives significantly nearer to the exchange?  If so, then a microwave link to their connection might be a possibility.    D b f i r s   11:28, 28 November 2014 (UTC)


 * DSL logs in with username and password. If the provider does not block second login, you will need an other DSL modem, line pair of wires to the DSLAM and a router with trhe ability of load balancing. Most providers cut double login due abuse or stolen login data (user and pass). It would be a long way of nogciation and minor chances of success. Using 2 different providers also requres router with load balancing functionality, but it will be able to route new connections trough the line with the less load. An second answer would be my interest, too. Most helpful would be to install a DSLAM (or repeater if exists) half way of the line. --Hans Haase (talk) 11:32, 28 November 2014 (UTC)


 * The second line should be separate wires and so could be with another ISP, thus avoiding problems with the double login. New wiring might give a slightly faster speed, but there could be a long delay before BT get round to installing the second line, and they will probably use the spare pair in the existing wiring to the house.  The repeater would be a good solution, but BT would have to install it and they are not known for helpfulness in solutions different from their standard setup.  You could try asking them to install a business line optimised for internet speed, but it will cost you more.    D b f i r s   08:44, 29 November 2014 (UTC)
 * For clarity, are you referring to the situation in the UK in particular? If not, it isn't true that DSL requires a username and password. Most implementations of DSL seem to use PPP (oA or oE) and so do require a username/password. However this isn't required by DSL (actually out Digital subscriber line suggests it was only added later), you can do IPoA and other things combined with either DHCP or fixed IP assignment and whether relying on the MAC address or simply not bothering with authentication. From what I read, it seems some ISPs do use username/password authentication even in these cases by transmitting it over the DHCP option 61 field . BTW, again without commenting on how things are done in the UK, even in cases where PPP with username/password is used, it's not always meaningful. In NZ, where PPPoA is often required (but I think not always over VDSL) the username/password used to be used and required for authetication. Nowadays it often doesn't matter if you put any random junk as the information isn't used for authentication. Most ISPs here use port authentication meaning they authenticate based on what the line is connected to at the DSLAM as I guess most people not using username/password at all or MAC address. Nil Einne (talk) 14:44, 30 November 2014 (UTC)

Thank you, everyone, for your suggestions and advice. I am going to pursue a second telephone line. The only houses we can see are even further out in the country so microwave is probably not an option. Last year our road was closed for a week while it was dug up to install major trunk electrical mains and fibre cables so at the time I asked if we could get a fibre connection. I was given a firm "no" even though the fibre runs right past our house. Thincat (talk) 15:55, 30 November 2014 (UTC)

which cryptographic operations are "commital"
Reading this, http://blog.cryptographyengineering.com/2014/11/zero-knowledge-proofs-illustrated-primer.html

(I'm not done reading), it does appear on requiring a "commitment". You can easily do this with client-server, and on each iteration the server can scramble colors and simply send all nodes each encrypted with a different key. You can then ask for an edge and the server will send you the key for that edge. (It doesn't really matter if this is symmetric or each edge is a public key/private key pair.)

But this only works if there is 100% guarantee that once you have a ciphertext, you can only get nothing (if you don't know the key) or the pre-committed plaintext. That there is no other plaintext that could be arrived at.

For example, the BEST possible symmetric key is the OTP. But this actually fails this test, because as long as the length is the same, the server could send one OTP "symmetric key" to give you "Blue...padding" another so you get "Red....padding" another for "Purple.padding" - in order not to leak information the padding needs to be there anyway.

So the perfect symmetric key actually does not ensure commitment.

1) What is this quality of commitment CALLED? 2) Which encryption algorithms have it and which don't?

I wonder, for example, whether a hash with a secure-none would have it? For example a node's plaintext might be "Session: Round:7 Node:7 Value is: Red securenonce: 345rhjdf2389ösdlfj3r9ufsd" and the server could send the SHA512 hash of this. The server therefore in the round send as many different SHA512 hashes as there are graph vertices, and then be willing to share the plaintext for any two of them for the round. (And be unwilling to share more for that round.) The recipient would be in possession of all the SHA512 hashes and therefore even though they would not see most of the vertices (they will only have two "decrypted") they can verify that they haven't changed.

Deos this scheme in fact have this property?

What encryption schems could be used instead? (such as separate private/public keypairs, with the private key simply being divulged for the ones that were chosen.) Thanks. 91.120.14.30 (talk) 12:46, 28 November 2014 (UTC)


 * Your hashing scheme does work, and it's mentioned in the article's final footnote.
 * Finding a key that decrypts a given ciphertext to a given plaintext is a known-plaintext attack. Modern block ciphers and stream ciphers are designed to prevent attacks of this type. A one-time pad is trivially vulnerable to it, as you said.
 * The prover has an easier problem in this case, though, since it can choose the "legitimate" key as well. Finding two keys that produce the same ciphertext from two given plaintexts is a form of collision attack. I don't know whether it has a more specific name, but for a block size of 128 bits it has a complexity of about 264 at most because of the birthday attack. Hash-based commitment has that problem too, though. You would probably need to use 256 bits per node for that reason. -- BenRG (talk) 19:01, 28 November 2014 (UTC)

returning computer to factory state
I have an HP 2000 laptop and want to wipe everything off it, that is, return it to factory new condition. Long ago I knew about a utility which would do that, and I'm sure the utility is still there, but I can't find anything (don't remember the name to search for it, and Help is no help.) Maybe since 20 years ago they have made it inaccessible to ordinary folks like me. But I would like to delete everything myself before I dispose of it. Is there anything I can do? Thanks. --50.80.235.249 (talk) 16:01, 28 November 2014 (UTC)
 * Perhaps you are recalling DBAN, a famous "boot and nuke" utility that wipes your harddrive, with the intent of deleting any and all personal data from the machine. This will not place the machine in "factory condition," though: it will leave the machine "wiped" and usually not able to boot until somebody installs new software.  If you really want to "restore to factory settings,", you will need to follow your system vendor's instructions.  Nimur (talk) 18:54, 28 November 2014 (UTC)


 * Searching for "hp 2000 factory reset" turned up this page, which says to press F11 during boot or run HP Recovery Manager from the start menu. -- BenRG (talk) 19:16, 28 November 2014 (UTC)

Why my computer quit working
Referring to this question, I had a clearer answer today. Sorry I never read the one response I got when I asked the question earlier, but I've seen it now.

When I got an error message this time after the computer not only shut down but wouldn't restart Windows until I asked the computer to repair itself, I got this message:


 * Troubleshoot a problem with your antivirus software
 * A problem related to your antivirus software caused your computer to shut down unexpectedly to protect itself from data corruption or loss.


 * To try to solve this problem, follow these steps. One step might solve the problem, but if it doesn't, then go on to the next step.


 * Update your antivirus software


 * Missing antivirus software updates could be the cause of your computer's problem. To make sure your antivirus is up to date, follow these steps:


 * Click to open Microsoft Security Center.
 * Click Malware protection.
 * If your software needs to be updated, click Update now.


 * If Windows can detect your antivirus software, it will be listed under Virus protection.
 * If your antivirus software is not displayed in Windows Security Center, go to the downloads section of your antivirus software provider’s website. Find the update for your version of the software and your operating system, and then install it. For more information, check the Help for your antivirus software.


 * Most antivirus software updates are free, but some providers charge a small fee for the updates. If you're using an older version of the software, you might also have to pay to upgrade to a more recent version to continue to receive the updates.


 * Check for multiple antivirus programs running on your computer


 * Running two antivirus software programs on your computer at the same time is not recommended because the two programs can interfere with each other. Even if you don't think your computer could be running two antivirus programs, antivirus software can sometimes come bundled with your computer and it might be running without your knowledge. To check if two antivirus programs are running, follow these steps:


 * Click the Start button, right-click Computer, and then click Manage. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.


 * In the left pane, double-click Services and Applications, and then click Services.


 * Look at the list of services under the Name column. If you find two antivirus programs, right-click each service associated with one of the programs, and then click Stop. Note that there may be multiple services running for one antivirus program.


 * Contact the antivirus manufacturer


 * If you've completed the previous steps, we recommend you contact the antivirus manufacturer directly for additional support.

I did everything I could and then tried to contact tech support. While I never got there because of problems I was never able to solve, I was told to use McAfee Virtual something or other to check the computer. I downloaded it and it did the checking and said it found four problems and could fix them. It seems to have done that. I will try McAfee tech support again when I figure out how, but until I turn on my computer tomorrow, maybe I won't have problems. Here's hoping the problem was solved.— Vchimpanzee  •  talk  •  contributions  •  20:26, 28 November 2014 (UTC)


 * You own this machine. The machine has this mainboard installed. The computer is equipped with a 250 Watts power supply without manufacturers information, but labeled by HP. HP often uses LiteOn power supplies. This generation of SMPSs usually uses lower switching frequency, makes need larger capacitors. I guess, the machine is 7 to 8 years old. The mainboard was manufactured by ASUS. All this is good quality. It is equipped with a less ammount of capacitors. It is possible the use of the machine, several hours daily, over night turned of, exceeded the capacitors livetime. This are passive devices under a higher work load. Typicial causes are: Sometimes the machine does not turn on, sporadic crashes, blue screens, failure in the first minutes since power up, random errors or freezing, difficult to differ in hard or software caused failures. It may be a short solution to install a new power supply. It will not run on the long term due the mainboard generates the core voltage for CPU and RAM from the 12 volts of the power supply while those voltags need to be stabilized as well. The components doing this are placed on the mainboard. There are several things more getting the machine older. Compared to an 1980s computer, it is rocket, more efficient but has a shorter lifetime. So what to do to solve this: Ensure the heat sinks are free from dust. Fans are operating. If you are not a person qualified to repair computers, television sets or similar, handling electronic and sensitive devices, of qualified to work with parts, operating with hazardous voltages, have somebody take a look who is educated and qualified is this. This minor visual check could also be done by a friend of you who has this knowledge. If everything is fine, check for malicious software and unneccessary burden of data. Windows Vista, you are using, should have the service packs and updated installed! On "my Computer", click the right button, choose properties. You should find the messages "Windows Vista" and "ServicePak 2". An antivirus software is required. Several products are free for home (private!) use. Not every software performs good on this machine. There are Microsoft Defender or Microsoft Security Essentials. If you are using old or bundled software what came installed on the computer, those security solutions will be obsolete, if no license upgrade was bought and installed. To secure some private data, there is Malwarebytes, see last answer. – btw I do not use. There is Crapcleaner to remove old temporary data and unneccessary things and clear cookies and caches. This speeds up the machine. It is recommended to create backups of all your data. First do so, if you do not have! If the failures will not end, it is hardware. As the mainboard complies the µATX form factor standard, a bundle of microATX/flexATX/ITX-mainboard, RAM and CPU including graphic adapter can be installed together with a new power supply meeting the new hardware's requirements. Before you buy, check prices and ensure the powersupply fits into the case. Windows must be reinstalled. So backup all data or get a new hard drive. Check prices on all work and the hardware to a new computer. --Hans Haase (talk) 07:33, 29 November 2014 (UTC) I posted this answer accedenty into the archive. --Hans Haase (talk) 16:49, 29 November 2014 (UTC)
 * Thanks. So far, since the "repair", everything seems fine. All this fixing sounds too complicated for me, so if it gets bad again and can't be fixed, I just may look at a new computer. In fact, I'll stop by the store where I got this one soon.— Vchimpanzee  •  talk  •  contributions  •  18:56, 30 November 2014 (UTC)