Php uniqid。 Generating Random String Using PHP

PHP: rfc:deprecate

If you want something a little more "random", just md5 uniqid. It seems like introducing non-determinism into a unit test would almost always be a bad idea. Finally, look at the speed consideration. It seems to me that if my code was incorrect it would have happened more than once. Given the same namespace and name, the output is always the same. ID created generated from the function is not unique because it is based on the system time and is not cryptographically secured. With an empty prefix, the returned string will be 13 characters long. Cryptographically Secure The function generates cryptographically secure pseudo-random bytes, which can later be converted to hexadecimal format using function. Further, passing its output to another function bin2hex , will give you unique random string. DUPLICATE UID WARNING: Be aware that calling this function many times in a tight loop for instance, to assign UIDs to objects in an array can result in many of the UIDs being identical, since less than a microsecond may have passed since the previous call. So it is advised that if the degree of randomness affect the security of an application, these methods should be avoided. 如果两个脚本恰好在相同的微秒生成 ID,该参数很有用。 I can't think of a good reason to use it. Usage of UUIDs on the Internet is described in. 0 , The prefix parameter became optional. With an empty prefix , the returned string will be 13 characters long. Neither the pseudo-random number rand nor the Mersenne Twister algorithms are cryptographically strong, and this is well known. com" url: text search for "text" in url selftext: text search for "text" in self post contents self:yes or self:no include or exclude self posts nsfw:yes or nsfw:no include or exclude results marked as NSFW e. Most of these notes are grossly wrong. I had a unit test suddenly start failing yesterday that had not failed since it was written months ago. Thus it should not be for cryptographical purposes. The clue to all this is where it says "more unique". The same goes for the v5 function which is always supplied a null URL. This function does not create random nor unpredictable string.。 You would need to pick the second from a 100,000 year range to get 42 bits of entropy. That's a deeply broken thing to do. First: you probably shouldn't be using uniqid at all. The test was for a form validator that only passed if the input was an integer and I was using uniqid to generate a random string. Since most systems adjust system clock by NTP or like, system time is changed constantly. This will break if you use it twice in quick succession, or if you have two different users at the same time, or if the phase of the moon is wrong. I'd recommend looking at the comments on the main PHP topic, notably: What I'd recommend is working out why you need uniqueness, is it for security i. Wikipedia's page on cryptographically-secure PRNGs explains. It doesn't matter what function you use to generate a 'random' string, or ID - if you don't double check that it isn't a duplicate, then there's always that chance. I assumed that it would make the tests more robust but clearly I was wrong in that assumption. It is a good PRNG for Monte Carlo simulations, not for anything related to security. Version 3 and 5 UUIDs are named based. The actual uniqid function takes seconds and microseconds of the current time, and returns the same in a hexadecimal form. 8 billion years to get them all. 1,The limit of 114 characters long for prefix was raised in this version. uniqid , against all expectations from the name, doesn't produce unique IDs. If you were just trying to make sure non-numeric strings were rejected by the validator, why not just hard code a few non-numeric strings? Examples: EA070 aBX32gTf APPROACH 1: Brute Force The first approach is the simplest one to understand and thus brute force. uniqid is not as "random" as you need. Usually, developers prefer uniqid function over rand , but did you know uniqid does not always guarantee uniqueness? Print the letter at that index. It ACTUALLY gets Unix time for the first 8 hex characters, then concatenates microseconds afterwards. Generate a random number using rand function. That only serves to virtually guarantee that you will eventually have a collision. This will make the result more unique. Version 4 UUIDs are pseudo-random. If you want something that's always unique, you'd need to implement a. When set to TRUE then return string will be 23 characters. I am just increasing base of UUID. Perform this step n times where n is the length of string required. Things are only unique if you check that they don't exist already. As a result, I blocked out many parts above, but I left much of it for posterity. Also, there is no usleep function in Windows. Well all of a sudden, uniqid started spitting out strings of digits only which were being cast to integers and the validator was letting them through. But, if there are two different processes that call uniqid at the very same time, there would be a microsecond delay in both of them and they might end up with the same uniqid sequence. And the v1 calls are very similar but just slightly different because it's based on the computer's MAC address and the current time. Hash it using one of the above functions. I use this function to generate microsoft-compatible GUID's. Generate Unique Alphanumeric String using uniqid function in PHP In PHP, there is a very helpful function uniqid which generates unique alphanumeric string for you. But then you would have keep all your values as strings. 定义和用法 uniqid 函数基于以微秒计的当前时间,生成一个唯一的 ID。 Few Reasons:• To generate an extremely difficult unique ID, use the md5 function. Third: to nodkz who wrote the clientIPToHex function - you reinvented so many wheels. Since most systems adjust system clock by NTP or like, system time is changed constantly. Although it could be just my bad programming, I found exactly 1 collission while debugging my code. The following class generates VALID RFC 4211 COMPLIANT Universally Unique IDentifiers UUID version 3, 4 and 5. Return Value: It returns timestamp based unique identifier as a string. 返回值 以字符串的形式返回唯一标识符。 The uniqid function in PHP is used to create random and unique sequence ids. uniqid uses microtime so, while for months it had been returning a string with alpha characters, it finally started returning strings with all digits pretty regularly. Parameters prefix Can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond. Note the line increases the likelihood that the result will be unique and not that is will guarantee uniqueness. Current implementation uses usleep 1 to generate unique ID based on microtime. Information labeled with UUIDs by independent parties can therefore be later combined into a single database, or transmitted on the same channel, without needing to resolve conflicts between identifiers. Seriously, avoid using this function. They require a namespace another valid UUID and a value the name. It is often used by PHP developers to create tokens for CSRF protection or sessions. Warning This function does not guarantee uniqueness of return value. Fourth: do not use random bytes for a unique identifier like hackan suggests. From there it is a question of how likely that is. Using usleep to make uniqid truly unique Since uniqid uses microseconds to determine a unique id every time, it could give the same sequence twice, if the function is called within the same microsecond. com find submissions from "example. For example, microtime now may be 12345678ae7f3 and in a week it may be 12345678e9a4c these numbers are simply for example. If you are storing the value to database it might be more efficient to use more letters than in hexadecimal, for me I decided 0-9a-z is good enough. 내장 함수 uniqid 가 있으므로 uniqid2 를 실제로 사용할 일은 없겠지만, 작동원리를 이해할 수 있다. Most systems adjust system time by NTP or similar. RFC 4122 requires a 128 bit value. First of all, we will understand why we might need unique alphanumeric id in first place. Below programs illustrate the uniqid function: Program 1: If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to contribute geeksforgeeks. As a result, there is no delay. Maybe to use as an identifier for a particular run of your script in logging, where you don't particularly care if there's a collision? Unique ID is needed if you have multiple-server app architecture i. These functions are not cryptographically secure random generators. Also, it provides a means by which to reverse-engineer the time when a uniqid was generated: date "r",hexdec substr uniqid ,0,8 ; Increasingly as you go further down the string, the number becomes "more unique" over time, with the exception of digit 9, where numeral prevalence is 0. While the probability that a UUID will be duplicated is not zero, it is so close to zero as to be negligible so that anyone can create a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Prefix can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond. 'create the Facebook instance before headers have been sent. If you want to merge different branches of data without clashes• With an empty prefix, the returned string will be 13 characters long. The PHP uniqid function has a more entropy flag, to make the output "more unique". But sometimes we need unique alphanumeric string as ids instead of simple integers. Also, How unique does it need to be? It returns a hexadecimal string. 70966391 As you can see above, we can use uniqid function in different ways to generate unique id. This may not be the best way to give this param variables, but it at least makes it work what appears to be properly generating unique ID's. The default value is FALSE, which returns 13 characters long string whereas when it is set to TRUE, the return string is 23 characters long. Note: The generated ID from this function is not optimal, because it is based on the system time. This is an inbuilt function of PHP. How you can have something which is more or less unique, is a bit confusing to me! All these function takes a string as an argument and output an Alpha-Numeric hashed string. It requires only one parameter - length, and it generates cryptographically secure pseudo-random bytes. With an empty prefix, the output string is 13 characters long. Hexadecimal strings can be decimal strings in fact, all decimal strings are syntactically valid hexadecimal strings. If you would generate 1 billion of Unique IDs per second, it would take about 781'904'565'217 times the current age of the Universe which is about 13. 为 ID 规定前缀。 Approach 3:Using uniqid function. ; While uniqid is based on the current time, the cautionary note above still applies - it just depends on where you will be using these "unique IDs". The function in PHP is an inbuilt function which is used to generate a unique ID based on the current time in microseconds micro time. MT, rand , and MD5 should NOT be used for encryption, or for cookies that that store a session ID that gives personal information. use the following search parameters to narrow your results: subreddit: subreddit find submissions in "subreddit" author: username find submissions by "username" site: example. You can 'endlessly' strive for uniqueness, up to a point, and enhance using any number of encryption routines, adding and the like- it depends on the purpose. Also they are not "4 digit sequeces", but 4 digit hexadecimal numbers. There will be periods of time where uniqid will have a much higher or lower chance of returning a string that will contain just digits 0-9 That was what I found interesting, that it was working for months before it started failing, even though it's perfectly obvious now that I know how uniqid works. To avoid this, usleep can be used inside the uniqid function. EDIT: So I made some assumptions and we all know what assuming does about how uniqid really works. While there is a sleep to prevent multiple duplicate IDs in the same process, there's no such guarantee and even a rather high probability of duplicate IDs with more processes or even multiple servers. So now you just have 5 bits of entropy in a system where the only returned characters are in base 16, and the numbers A through F account for over a third of the characters. UUIDs generated below validates using OSSP UUID Tool, and output for named-based UUIDs are exactly the same. Unique ID is helpful and must if you want to prevent sequence discovery of data in application or API endpoints. The first two arguments have been demonstrated below and are straightforward, so I'll skip to the as-yet non-described arguments. If used, PHP just skips the usleep function and keeps going on. This is due to uniqid being time based and adding only insufficient random. 1, prefix could only be a maximum of 114 characters long. This function must not be used for security purposes. This tool generates unique identifier numbers: a UUID Universally Unique IDentifier , GUID Globally Unique IDentifier , or Unique ID, is a 128-bit number used to identify uniquely information or resources. I don't see what the shock was here? e - Your database is stored in multiple servers• Notice that it's going to take a long time for those first 8 digits to change. Generate random index from 0 to string length-1. If you need to generate cryptographically secure tokens use. Checking as above, and combining all this stuff will let you end up with something approaching uniqueness, but its all relative to where the keys will be used and the context. Anyway, it doesn't really matter how random the input is, I just wanted an easy way to get a randomized string. I also don't see why randomness was required? This builds slightly on david's post below. Mersenne Twister is a fast algorithm with good k-distribution which will give you numbers for a long time before it repeats itself. Parameters used in uniqid There are two types of parameters in uniqid : Prefix: It is just a string which can be added on before the uniqid output. Basically, usleep delays the entire execution by one microsecond, which makes uniqid truly unique. session cookies , it is recommended that you use something along these lines: This will create a 32 character identifier a 128 bit hex number that is extremely difficult to predict. You should uses this function instead. The correct approach is to use the unique ID on its own; it's already geared for non-collision. prefix became optional in PHP 5 but can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond. So if you want to generate string of a fixed length, you can either truncate the generated string or concatenate with another string, based on the requirement. See your article appearing on the GeeksforGeeks main page and help other Geeks. The uniqid function in PHP is an inbuilt function which is used to generate a unique ID based on the current time in microseconds micro time. This is a pure PHP implementation. By default, it returns a 13 character long unique string. IDs should never be obfuscated for security, so if you're worried about someone guessing your ID, fix the system, don't just make it harder to guess because it's nowhere near as difficult to guess as you imagine: you can just brute force the 60,000 MD5s that are generatable from millisecond IDs over the course of a given minute, which the typical computer can do in less than 0. And This function does not generate cryptographically secure tokens, in fact without being passed any additional parameters the return value is little different from. The php5-uuid functions could definitely use some documentation to clarify how they should be used, but here's what I've gleaned by examining the OSSP source code found here:. Suitability will change with the underlying considerations. System time is adjusted by magnitude of milliseconds or even seconds constantly. 9 bits of entropy, tops in reality probably less as LCG is not a cryptographically secure pseudorandom number generator. One simple solution is to compare the latest value returned with the previous result, and keep calling in a loop until the new value is different, if you don't mind this call causing a delay of 1 microsecond per call when necessary. Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below. 'will cause authentication issues after the first request. Simply combining non-cryptographically strong algorithms doesn't not make a cryptographically strong algorithm either. The real lesson might be to not use randomized data in your unit tests, or, if you do, at least make sure to understand all potential outputs. A simple application where non-collision of session IDs is highly preferred but not critical, such as storing a user's shopping cart items for when they return to your site but not their personal information , IS a good use for the MT, rand MD5, uniqid and combinations thereof. The answer is, not very, but not to a discountable degree. Examples If you need a unique identifier or token and you intend to give out that token to the user via the network i. Errors And Exceptions• 说明 如果 prefix 参数为空,则返回的字符串有 13 个字符串长。

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uniqid

In conclusion With so many other options available in PHP to generate sequences, it is safe to say that uniqid is probably one of the most efficient and customizable. Store all the possible letters into a string. Second: don't rely on the output of uniqid to be, in any way, unique. If you absolutely need to involve a hash somehow - maybe to placate a boss who thinks they understand security much better than they actually do - append it instead. You can use random bytes, and get another set of random bytes if there's a collision. To learn more about these functions Once we understand how we utilize these functions, our task becomes pretty simple. I have been using mimecs version lately and do not think it's safe to think the results are always unqiue. This is why it has microsecond precision. uniqid , to those who don't know, is simply a hexadecimal representation of the current time in microseconds unix time with microseconds concatenated on. The v4 UUIDs are always entirely different because they are pseudo random. It can be achieved as follows:• The exact numbers of entropy are not "correct" in a practical sense, but the theory is still correct that "There will be periods of time where uniqid will have a much higher or lower chance of returning a string that will contain just digits 0-9. Setting more-entropy to true generates a more unique value, however the execution time is longer though to a tiny degree , according to the docs: If set to TRUE, uniqid will add additional entropy using the combined linear congruential generator at the end of the return value, which increases the likelihood that the result will be unique. The ID generated from the uniqid function is not optimal since it is based on the system time and is not cryptographically secured. Pretty much anything else will eventually collide since there's only so much entropy in the function. Generate a random, unique, alpha-numeric string using PHP. I recommend anyone to include time as a factor of such an ID as to be a little more certain it is in fact unique. Update, March 2014: Firstly, it is important to note that uniqid is a bit of a misnomer as it doesnt guarantee a unique ID. ircmaxell where does that number come from? Default is FALSE and the return string will be 13 characters long. PHP: How to generate a Unique id in PHP Alphanumeric String By Parth Patel on Feb 25, 2020 In php, there are many ways to generate unique alphanumeric id. To understand why that's not good for uniqueness, see. uniqid 와 동일한 기능을 가지는 uniqid2 를 만들어 보았다. This question isn't really a problem looking for a solution, it's more just a matter of simple curiosity. As such, for each iteration there is about after some quick math 8. but it's a lot easier to just use a sequential identifier like you should, possibly along with a random key Here is my approach to generate short string unique id. 规定位于返回值末尾的更多的熵。 。 。 。 。 。 。

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