Wikipedia:Reference desk/Archives/Computing/2015 March 13

= March 13 =

PC rating in Window 7
pc rating in win 7.what is it & after rated what do the numbers mean? — Preceding unsigned comment added by 219.94.83.162 (talk) 03:48, 13 March 2015 (UTC)


 * Do you mean the performance ratings where it lists various characteristics of your PC, like RAM, rates how good each is, then comes up with a composite performance rating for the PC as a whole ? StuRat (talk) 05:50, 13 March 2015 (UTC)


 * See Windows System Assessment Tool. --  Gadget850talk 13:30, 13 March 2015 (UTC)

SHA-256
I've recently added a SHA-256 commitment to my account, but I can't for the life of me figure out how to reverse this. I clearly have both the commitment and the pass-phrase, but every program I find only encrypts and doesn't decrypt. I'm using SHA-256 HMAC, and if anybody knows any programs to reverse it that would be great. Thanks!  Kharkiv07 Talk  04:45, 13 March 2015 (UTC)


 * I'm not sure exactly what you mean. However, the confusion might arise because SHA-256 is a cryptographic hash and not an encryption scheme.  In general, it is not possible to take the output of a SHA-256 process and determine what the input was.  One can however verify that a specific input gives that output.  In that sense it is a one-way function, allowing people to generate specific output from specific input, but no one can discover the input simply from seeing the output.  Dragons flight (talk)


 * The user added User committed identity to their user page. --  Gadget850talk 07:33, 13 March 2015 (UTC)


 * Yes, I'm just trying to see, just out of curiosity, how I can take my key and that commitment and get the original string back out.  Kharkiv07 Talk  12:34, 13 March 2015 (UTC)
 * The whole point of a cryptographically secure one-way hash, which SHA-256 is an implementation of, is that it is impossible to get the original string back. The way wikipedia uses them is that, if you need to use it to recover your account, you send the original phrase to a trusted member of the WP community. They will run SHA-256 on it, and check that the hash is the same as the one on your userpage. It is (almost) impossible for anyone who doesn't know the phrase to come up with a matching one. LongHairedFop (talk) 13:19, 13 March 2015 (UTC)
 * The pigeonhole principle explains why it is truly impossible (as opposed to just difficult) to get the original string back. It's a good concept to understand, whatwith the compression algorithm investment scam and such. 88.112.50.121 (talk) 20:41, 13 March 2015 (UTC)
 * That principle also explains why it is not guaranteed to be absolutely secure, though I agree that it is practically impossible to get the original string.   D b f i r s   22:05, 13 March 2015 (UTC)
 * If the original string is significantly longer than 256 bits, there are just about guaranteed to be multiple original strings, which is what the pigeonhole principle is talking about. (However, most of them are likely to be gibberish, as discussed at unicity distance.)
 * If the original string is shorter than 256 bits, I don't think the pigeonhole principle applies at all. —Steve Summit (talk) 22:18, 13 March 2015 (UTC)


 * Okay I did have some confusion, but I think I'm good. Thanks y'all!  Kharkiv07 Talk  23:10, 13 March 2015 (UTC)
 * Be sure to read the "choosing a good string" section. If your string would be easy to guess for someone who knew your real-life identity and suspected the account was yours, they could easily reproduce the hash by guessing the the string. A dedicated impersonator who knew your address, the name of your pet, the licence number of your car, your mother's maiden name, etc. could even write a program that combined such pieces of information into strings, and use a rainbow table approach to cracking your passphrase. --NorwegianBluetalk 09:36, 14 March 2015 (UTC)