No User Modification That Changed The Games Checksum
Despite having no mods on when I try to start a single player game in ironman mode it tells me ironman mode is disabled. Under the tooltip it shows '(X) No User Modification that change the game's checksum must be active' but there's definitely nothing like that, and I can start the game in ironman mode until I use the custom ruler thing. Self:yes (or self:no) include (or exclude) self posts nsfw:yes (or nsfw:no) include (or exclude) results marked as NSFW. Subreddit:aww site:imgur.com dog. See the search faq for details.
I have 2 excel documents and I want to check if they are exactly the same, apart from the file name.For example, the files are called fileone.xls and filetwo.xls. Apart from the file names, their contents are presumed to be identical but this is what i want to check.I've been looking for ways to review this and without installing a bunch of plugins. There doesn't seem a straight forward way.I've tried generating MD5 hashes for both files. When the hashes are identical, does this mean that the file contents are 1:1 the same? When the hashes are identical, does this mean that the file contents are 1:1 the same?All files are a collection of bytes (values 0-255). If two files MD5 hashes match, both those collections of bytes are extremely likely the exact same (same order, same values).There's a very small chance that two files can generate the same MD5, which is a 128 bit hash. The probability is:Probability of just two hashes accidentally colliding is 1/2 128 whichis 1 in 340 undecillion 282 decillion 366 nonillion 920 octillion 938septillion 463 sextillion 463 quintillion 374 quadrillion 607 trillion431 billion 768 million 211 thousand 456.
(from an answer on.)Hashes are meant to work in 'one direction only' - i.e. You take a collection of bytes and get a hash, but you can't take a hash and get back a collection of bytes.Cryptography depends on this (it's one way two things can be compared without knowing what those things are.)Around the year 2005, methods were discovered to take an MD5 hash and create data that matches that hash create two documents that had the same MD5 hash. This means an attacker can create two executables, for example, that have the same MD5, and if you are depending on MD5 to determine which to trust, you'll be fooled.Thus MD5 should not be used for cryptography or security. It's bad to publish an MD5 on a download site to ensure download integrity, for example.
Depending on an MD5 hash you did not generate yourself to verify file or data contents is what you want to avoid.If you generate your own, you know you're not being malicious to yourself (hopefully). So for your use, it's OK, but if you want someone else to be able to reproduce it, and you want to publicly publish the MD5 hash, a better hash should be used.Note that it's possible for two Excel files to contain the same values in the same rows and columns, but for the bytestream of the file to be completely different due to different formatting, styles, settings, etc.If you are wanting to compare the data in the file, export it to CSV with the same rows and columns first, to strip out all formatting, and then hash or compare the CSV's.
In practice, yes, an identical cryptographic hash means the files are the same, as long as the files were not crafted by an attacker or other malicious entity. The odds of random collisions with any well-designed cryptographic hash function is so small as to be negligible in practice and in the absence of an active attacker.In general, however, no, we cannot say that two arbitrary files having the same hash definitely means that they are identical.The way a cryptographic hash function works is to take an arbitrary-length input, and output a fixed-length value computed from the input.
Some hash functions have multiple output lengths to choose from, but the output is still to some degree a fixed-length value. This value will be up to a few dozen bytes long; the hash algorithms with the longest output value in common use today have a 512-bit output, and a 512-bit output is 64 bytes.If an input to a hash function is longer than the output of the hash function, some fidelity must be removed to make the input fit in the output. Consequently, there must exist multiple inputs of lengths greater than the length of the output, which generate the same output.Let's take the current workhorse, SHA-256, as an example. It outputs a hash of 256 bits, or 32 bytes.
If you have two files which are each exactly 32 bytes long, but different, these should (assuming no flaw in the algorithm) hash to different values, no matter the content of the files; in mathematical terms, the hash is a function mapping a 2 256 input space onto a 2 256 output space, which should be possible to do without collisions. However, if you have two files that are each 33 bytes long, there must exist some combination of inputs that give the same 32-byte output hash value for both files, because we're now mapping a 2 264 input space onto a 2 256 output space; here, we can readily see that there should, on average, exist 2 8 inputs for every single output. Take this further, and with 64-byte files there should exist 2 256 inputs for every single output!Cryptographic hash functions are designed such that it's computationally difficult to compose an input that gives a particular output, or compose two inputs that give the same output. This is known as resistance or resistance. It's not impossible to find these collisions; it's just intended to be really, really, really, really hard. (A bit of a special case of a collision attack is a.)Some algorithms are better than others at resisting attackers.
MD5 is generally considered completely broken these days, but last I looked, it still sported pretty good first preimage resistance. SHA-1 is likewise effectively broken; preimage attacks have been demonstrated, but require specific conditions, though there's no reason to believe that will be the case indefinitely; as the saying goes, attacks always get better, they never get worse. SHA-256/384/512 are currently still believed safe for most purposes. However, if you're just interested in seeing if two non-maliciously-crafted, valid files are the same, then any of these should be sufficient, because the input space is sufficiently constrained already that you'd be mostly interested in random collisions. If the hashes match then either the files are a result of a deliberate collision, or they aren't and then they are guaranteed to be the same. The probability of an accidental collision is purely theoretic.
Saying that “if the hashes match then they are highly likely to appear the same” is misleading: if there's malice afoot and it's a collision situation then they aren't likely to be the same, and otherwise the probability is effectively zero, it isn't some low-probability event that needs to be defended against.–May 21 '18 at 21:43. @Gilles: On the contrary. Michael's wording is exactly right, and 'guaranteed' is misleading (or, well, factually wrong). The likelihood of two files with identical hashes not matching (notwithstanding malicious modification) is extremely low, and can be neglected in practice. It is, however, not zero. There is generally a chance, that for whatever reason different inputs will produce the same hash, and possibly even with a likelihood much higher than 2^-128 (cryptographic algorithms are black art, the algortihm may be flawed in a subtle, unknown way and we have no way of being 100% sure).–May 22 '18 at 10:15.
It's a probability game. Hashes are able to represent a finite number of values.If we consider a hypothetical (and very weak) 8-bit hashing algorithm, then this can represent 256 distinct values. As you start to run files through the algorithm, you will start to get hashes out. But before long you will start to see '. This means that two different files were fed into the algorithm, and it produced the same hash value as its output.
@mbrig: A 32-bit hash would have a significant risk of accidental mismatch. Going to 128 or 256 bits, however, makes a huge difference. With 128 bits, a billion monkeys each typing a billion decently-sized genuinely-random documents would have about a 0.3% chance of creating two documents with the same hash. With 256 bits, even if billions monkeys could type a billion decently-sized random documents per second for a billion years, the likelihood of any of those nonillions of documents having coincidentally-matching hash values would be vanishingly small.–May 22 '18 at 19:12. If two files have the same MD5 hash, and they haven't both been specially crafted, then they're identical. How hard it is to craft files with the same MD5 hash depends on the file format, I don't know how easy it is with Excel files.So if you have files of your own that are just lying around and want to find duplicates, MD5 is safe.
If you wrote one of the files, and the other file is of dubious origin, MD5 is still safe (the only way to get different files with the same MD5 checksum is to craft both files). If someone you don't trust sends you a budget proposal, and later sends another file which they claim is the same, then MD5 may not be enough.To avoid any risk, use SHA-256 or SHA-512 instead of MD5.
If two files have the same SHA-256 hash, then they're identical. The same goes for SHA-512. (There's a theoretical possibility that they could be different, but the probability of this happening accidentally is so much less than the probability of your computer flipping a bit during the verification than it just isn't relevant.
As for someone deliberately crafting two files with the same hash, nobody knows how to do this for SHA-256 or SHA-512.)If two Excel files have different hashes, then they're different, but there's no way to know by how much they differ. They could have identical data but different formatting, or they could just differ in the properties, or they might have been saved by different versions. In fact if Excel is anything like Word then merely saving a file updates its metadata. If you only want to compare the numerical and text data and ignore formatting and properties, you can export the spreadsheets to CSV to compare them.If you have Unix/Linux tools available, then you can use cmp to compare two files. To compare two files on the same machine, checksums only make things more complicated. If two files have the same MD5 hash, and they haven't both been specially crafted, then they're identical.
That is incorrect. There are an infinity of possible messages, yet there are only 2^64 possible 64-bit hashes.
Ck2 Beta Access Code
It's called the: ' the pigeonhole principle states that if n items are put into m containers, with n m, then at least one container must contain more than one item.' If you create more than 2^64 messages you will have collisions without any 'special crafting'. And you might with just 2.–May 26 '18 at 20:45. Being effectively equivalent to random distribution is part of the definition of what constitutes a good cryptographic hash - you have a lot of rounds of mixing for a reason. Certainly, there are weak hash algorithms, but focusing on those weaknesses gets us into the previously-stated caveats around intentional attacks. (Or are you saying that MD5 has been shown to only have 64 bits that are effectively random?
I'll admit that I haven't been keeping up, so that's plausible - link please?)–May 27 '18 at 0:14. @AndrewHenle I do not state that a collision is mathematically impossible, which would be wrong, but not relevant here.
I state that it has not happened, which is true. Your comment is incorrect in a way that completely changes the deal. There are 2^128 possible MD5 hashes, not 2^64. This means you would need to generate 2^128 hashes to be certain to generate a collision. Actually, by the birthday paradox, 2^64 would give you a macroscopic chance of a collision between the hashes you generated (not with a previously-generated hash). But this is moot since we know how to craft collision.–May 27 '18 at 9:46.
Short answer: A is supposed to help you be reasonably confident that files with matching hashes are the same. Unless deliberately crafted, the chances of two slightly different files having similar hash values is ridiculously small. But when it comes to comparing and verifying files that could be deliberately tampered with, MD5 is poor choice. (Use another hash function like SHA3 or BLAKE2.)Long answer: An ideal hash function is one that creates an almost unique cryptographic hash for a every unique piece of data.
In other words, we definitely know that there are two files in this universe whose hash values collide, the chance of these two files naturally coming together is ridiculously small.Ten years ago, I decided I must stay as far as I can from MD5. (Of course, until yesterday, I remembered the wrong reason for doing so; ten years is a long time, you see. I revisited my past memos to remember why and edited this answer.) 9 years later, researchers were able to create pairs of PostScript documents and (ouch!) X.509 certificates with the same hash! MD5 was clearly broken.
(Megaupload.com was also using MD5, and there was a lot of hanky-panky around hash collisions that gave me trouble at the time.)So, I concluded that while MD5 was (and still is) reliable for comparing benign files, one must stop using it altogether. I reasoned that reliance on it has the risk of turning into indulgence and false confidence: Once you start comparing files using their MD5 hashes, one day you forget the security fineprint and compare two files that are deliberately crafted to have the same hash. In addition, CPUs and cryptoprocessors were unlikely to add support for it.The original poster, however, has even less reasons to use MD5, because:. As long as one is comparing two files only, byte-for-byte comparison is actually faster than generating one's own MD5 hashes. For comparing three or more files. Well, now you have a legitimate cause.
The OP specified 'ways to review this and without installing a bunch of plugins'. Windows PowerShell's command can generate SHA1, SHA256, SHA384, SHA512 and MD5 hashes. On modern computers with hardware support for SHA hash functions, generating them is faster.