PHP How to generate a random unique alphanumeric string for use in a secret link

Question

How would it be possible to generate a random  unique string using numbers and letters for use in a verify link  Like when you create an account on a website  and it sends you an email with a link  and you have to click that link in order to verify your account How can I generate one of those using PHP

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function random string  length   8         alphabets   range  A   Z         numbers   range  0   9         additional characters   array                final array   array merge  alphabets  numbers  additional characters          while  length--           key   array rand  final array           password     final array  key                               if  preg match    A-Za-z0-9      password              return  password       else      return  random string

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PHP 7 standard library provides the random bytes  length  function that generate cryptographically secure pseudo-random bytes  Example   bytes   random bytes 20   var dump bin2hex  bytes     The above example will output something similar to  string 40   quot 5fe69c95ed70a9869d9f9af7d8400a6673bb9ce9 quot   More info  http   php net manual en function random-bytes php PHP 5  outdated  I was just looking into how to solve this same problem  but I also want my function to create a token that can be used for password retrieval as well  This means that I need to limit the ability of the token to be guessed  Because uniqid is based on the time  and according to php net  quot the return value is little different from microtime   quot   uniqid does not meet the criteria  PHP recommends using openssl random pseudo bytes   instead to generate cryptographically secure tokens  A quick  short and to the point answer is  bin2hex openssl random pseudo bytes  bytes    which will generate a random string of alphanumeric characters of length    bytes   2  Unfortunately this only has an alphabet of  a-f  0-9   but it works   Below is the strongest function I could make that satisfies the criteria  This is an implemented version of Erik s answer   function crypto rand secure  min   max         range    max -  min      if   range  lt  1  return  min     not so random         log   ceil log  range  2         bytes    int    log   8    1     length in bytes      bits    int   log   1     length in bits      filter    int   1  lt  lt   bits  - 1     set all lower bits to 1     do            rnd   hexdec bin2hex openssl random pseudo bytes  bytes              rnd    rnd  amp   filter     discard irrelevant bits       while   rnd  gt   range       return  min    rnd     function getToken  length         token    quot  quot        codeAlphabet    quot ABCDEFGHIJKLMNOPQRSTUVWXYZ quot        codeAlphabet    quot abcdefghijklmnopqrstuvwxyz quot        codeAlphabet    quot 0123456789 quot        max   strlen  codeAlphabet      edited      for   i 0   i  lt   length   i               token     codeAlphabet crypto rand secure 0   max-1               return  token     crypto rand secure  min   max  works as a drop in replacement for rand   or mt rand  It uses openssl random pseudo bytes to help create a random number between  min and  max  getToken  length  creates an alphabet to use within the token and then creates a string of length  length  Source  http   us1 php net manual en function openssl-random-pseudo-bytes php 104322

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I think this is the best method to use   str shuffle md5 rand 0 100000

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You can use UUID Universally Unique Identifier   it can be used for any purpose  from user authentication string to payment transaction id   A UUID is a 16-octet  128-bit  number  In its canonical form  a UUID is represented by 32 hexadecimal digits  displayed in five groups separated by hyphens  in the form 8-4-4-4-12 for a total of 36 characters  32 alphanumeric characters and four hyphens    function generate uuid         return sprintf    04x 04x- 04x- 04x- 04x- 04x 04x 04x           mt rand  0  0xffff    mt rand  0  0xffff            mt rand  0  0xffff            mt rand  0  0x0C2f     0x4000          mt rand  0  0x3fff     0x8000          mt rand  0  0x2Aff    mt rand  0  0xffD3    mt rand  0  0xff4B                 calling funtion   transationID   generate uuid      some example outputs will be like   E302D66D-87E3-4450-8CB6-17531895BF14 22D288BC-7289-442B-BEEA-286777D559F2 51B4DE29-3B71-4FD2-9E6C-071703E1FF31 3777C8C6-9FF5-4C78-AAA2-08A47F555E81 54B91C72-2CF4-4501-A6E9-02A60DCBAE4C 60F75C7C-1AE3-417B-82C8-14D456542CD7 8DE0168D-01D3-4502-9E59-10D665CEBCB2   hope it helps someone in future

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Object-oriented version of the most up-voted solution  I ve created an object-oriented solution based on Scott s answer    lt  php  namespace Utils          Class RandomStringGenerator     package Utils       Solution taken from here     http   stackoverflow com a 13733588 1056679     class RandomStringGenerator            var string        protected  alphabet            var int        protected  alphabetLength                    param string  alphabet             public function   construct  alphabet                     if          alphabet                 this- gt setAlphabet  alphabet             else                this- gt setAlphabet                    implode range  a    z                      implode range  A    Z                      implode range 0  9                                                   param string  alphabet             public function setAlphabet  alphabet                 this- gt alphabet    alphabet           this- gt alphabetLength   strlen  alphabet                          param int  length         return string             public function generate  length                 token                for   i   0   i  lt   length   i                   randomKey    this- gt getRandomInteger 0   this- gt alphabetLength                token     this- gt alphabet  randomKey                      return  token                         param int  min         param int  max         return int             protected function getRandomInteger  min   max                 range     max -  min            if   range  lt  0                   Not so random                return  min                      log   log  range  2               Length in bytes           bytes    int    log   8    1              Length in bits           bits    int   log   1              Set all lower bits to 1           filter    int   1  lt  lt   bits  - 1           do                rnd   hexdec bin2hex openssl random pseudo bytes  bytes                     Discard irrelevant bits               rnd    rnd  amp   filter             while   rnd  gt    range            return   min    rnd               Usage   lt  php  use Utils RandomStringGenerator      Create new instance of generator class   generator   new RandomStringGenerator      Set token length   tokenLength   32      Call method to generate random string   token    generator- gt generate  tokenLength     Custom alphabet  You can use custom alphabet if required  Just pass a string with supported chars to the constructor or setter    lt  php   customAlphabet    0123456789ABCDEF       Set initial alphabet   generator   new RandomStringGenerator  customAlphabet       Change alphabet whenever needed   generator- gt setAlphabet  customAlphabet     Here s the output samples  SRniGU2sRQb2K1ylXKnWwZr4HrtdRgrM q1sRUjNq1K9rG905aneFzyD5IcqD4dlC I0euIWffrURLKCCJZ5PQFcNUCto6cQfD AKwPJMEM5ytgJyJyGqoD5FQwxv82YvMr duoRF6gAawNOEQRICnOUNYmStWmOpEgS sdHUkEn4565AJoTtkc8EqJ6cC4MLEHUx eVywMdYXczuZmHaJ50nIVQjOidEVkVna baJGt7cdLDbIxMctLsEBWgAw5BByP5V0 iqT0B2obq3oerbeXkDVLjZrrLheW4d8f OUQYCny6tj2TYDlTuu1KsnUyaLkeObwa     I hope it will help someone  Cheers

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Simplifying Scotts code above by removing unnecessary loops which is slowing down badly and does not make it any more secure than calling openssl random pseudo bytes just once  function crypto rand secure  min   max      range    max -  min   if   range  lt  1  return  min     not so random      log   ceil log  range  2      bytes    int    log   8    1     length in bytes   rnd   hexdec bin2hex openssl random pseudo bytes  bytes      return  min    rnd  range     function getToken  length     return bin2hex openssl random pseudo bytes  length

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When trying to generate a random password you are trying to     First generate a cryptographically secure set of random bytes Second is turning those random bytes into a printable string   Now  there are multiple way to generate random bytes in php like     length   32     PHP 7   bytes  random bytes  length      PHP  lt  7  bytes  openssl random pseudo bytes  length     Then you want to turn these random bytes into a printable string    You can use bin2hex     string   bin2hex  bytes     or base64 encode     string   base64 encode  bytes     However  note that you do not control the length of the string if you use base64  You can use bin2hex to do that  using 32 bytes will turn into a 64 char string  But it will only work like so in an EVEN string   So basically you can just do     length   32   if PHP VERSION gt  7        bytes  random bytes  length    else       bytes  openssl random pseudo bytes  length        string   bin2hex  bytes

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I like to use hash keys when dealing verification links  I would recommend using the microtime and hashing that using MD5 since there should be no reason why the keys should be the same since it hashes based off of the microtime     key   md5 rand       key   md5 microtime

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we can use this two line of code to generate unique string have tested around 10000000 times of iteration      sffledStr  str shuffle  abscdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890       amp     -          uniqueString   md5 time    sffledStr

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Here is what I use   md5 time     rand            Creates something like 0c947c3b1047334f5bb8a3b7adc1d97b

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Use the code below to generate the random number of 11 characters or change the number as per your requirement    randomNum substr str shuffle  0123456789abcdefghijklmnopqrstvwxyz    0  11     or we can use custom function to generate the random number   function randomNumber  length         numbers   range 0 9        shuffle  numbers        for  i   0  i  lt   length  i             digits     numbers  i        return  digits         generate random number   randomNum randomNumber 11

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Generate a random number using your favourite random-number generator Multiply and divide it to get a number matching the number of characters in your code alphabet Get the item at that index in your code alphabet   Repeat from 1  until you have the length you want   e g  in pseudo code   int myInt   random 0  numcharacters  char   codealphabet    ABCDEF12345  char random   codealphabet i  repeat until long enough

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Scott  yes you are very write and good solution  Thanks   I am also required to generate unique API token for my each user  Following is my approach  i used user information  Userid and Username    public function generateUniqueToken  userid   username             rand   mt rand 100 999        md5   md5  userid     amp   532567 465       username         md53   substr  md5 0 3        md5 remaining   substr  md5 3         md5    md53   rand   userid   md5 remaining       return  md5      Please have a look and let me know if any improvement i can do  Thanks

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after reading previous examples I came up with this   protected static  nonce length   32   public static function getNonce          chars   array        for   i   0   i  lt  10   i             chars   array merge  chars  range 0  9   range  A    Z         shuffle  chars        start   mt rand 0  count  chars  - self   nonce length       return substr join      chars    start  self   nonce length       I duplicate 10 times the array 0-9 A-Z  and shuffle the elements  after I get a random start point for substr   to be more  creative     you can add  a-z  and other elements to array  duplicate more or less  be more creative than me

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This is a simple function that allows you to generate random strings containing Letters and Numbers  alphanumeric   You can also limit the string length  These random strings can be used for various purposes  including  Referral Code  Promotional Code  Coupon Code  Function relies on following PHP functions  base convert  sha1  uniqid  mt rand  function random code  length      return substr base convert sha1 uniqid mt rand      16  36   0   length      echo random code 6      sample output   a7d9e8   3klo93

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For really random strings  you can use   lt  php  echo md5 microtime true  mt Rand       outputs    40a29479ec808ad4bcff288a48a25d5c   so even if you try to generate string multiple times at exact same time  you will get different output

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A simple solution is to convert base 64 to alphanumeric by discarding the non-alphanumeric characters  This one uses random bytes   for a cryptographically secure result  function random alphanumeric int  length   string        result         do                 Base 64 produces 4 characters for each 3 bytes  so most times this will give enough bytes in a single pass          bytes random bytes   length 3-strlen  result   2             Discard non-alhpanumeric characters          result  str replace                          base64 encode  bytes              Keep adding characters until the string is long enough           Add a few extra because the last 2 or 3 characters of a base 64 string tend to be less diverse      while strlen  result  lt  length 3       return substr  result 0  length      Edit  I just revisited this because I need something a bit more flexible  Here is a solution that performs a bit better than the above and gives the option to specify any subset of the ASCII character set   lt  php class RandomText       protected          allowedChars            Maximum index to use          allowedCount            Index values will be taken from a pool of this size           It is a power of 2 to keep the distribution of values even          distributionSize            This many characters will be generated for each output character          ratio                  param string  allowedChars characters to choose from             public function   construct string  allowedChars                 this- gt allowedCount   strlen  allowedChars           if  this- gt allowedCount  lt  1     this- gt allowedCount  gt  256  throw new  Exception  At least 1 and no more than 256 allowed character s  must be specified              this- gt allowedChars    allowedChars            Find the power of 2 equal or greater than the number of allowed characters          this- gt distributionSize   pow 2 ceil log  this- gt allowedCount  2               Generating random bytes is the expensive part of this algorithm           In most cases some will be wasted so it is helpful to produce some extras  but not too many           On average  this is how many characters needed to produce 1 character in the allowed set           50  of the time  more characters will be needed  My tests have shown this to perform well           this- gt ratio    this- gt distributionSize    this- gt allowedCount                         param int  length string length of required result         return string random text             public function get int  length    string               if  length  lt  1  throw new  Exception   length must be  gt   1              result                 Keep track of result length to prevent having to compute strlen            l   0           indices   null           i   null          do                         Bytes will be used to index the character set  Convert to integers               indices   unpack  C    random bytes ceil   length -  l     this- gt ratio                 foreach  indices as  i                                  Reduce to the smallest range that gives an even distribution                  i     this- gt distributionSize                    If the index is within the range of characters  add one char to the string                 if  i  lt   this- gt allowedCount                                         l                         result     this- gt allowedChars  i                                     if  l  gt    length  break                         while  l  lt   length           return  result

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This function will generate a random key using numbers and letters   function random string  length         key            keys   array merge range 0  9   range  a    z          for   i   0   i  lt   length   i               key     keys array rand  keys               return  key     echo random string 50     Example output   zsd16xzv3jsytnp87tk7ygv73k8zmr0ekh6ly7mxaeyeh46oe8

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If you want to generate a unique string in PHP  try following   md5 uniqid   mt rand       In this   uniqid   - It will generate unique string  This function returns timestamp based unique identifier as a string   mt rand   - Generate random number   md5   - It will generate the hash string

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I m late but I m here with some good research data based on the functions provided by Scott s answer  So I set up a Digital Ocean droplet just for this 5-day long automated test and stored the generated unique strings in a MySQL database  During this test period  I used 5 different lengths  5  10  15  20  50  and   -0 5 million records were inserted for each length  During my test  only the length 5 generated   -3K duplicates out of 0 5 million and the remaining lengths didn t generate any duplicates  So we can say that if we use a length of 15 or above with Scott s functions  then we can generate highly reliable unique strings  Here is the table showing my research data   Update  I created a simple Heroku app using these functions that returns the token as a JSON response  The app can be accessed at https   uniquestrings herokuapp com api token length 15 I hope this helps

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I use this one-liner   base64 encode openssl random pseudo bytes 3     length  gt  gt  2       where length is the length of the desired string  divisible by 4  otherwise it gets rounded down to the nearest number divisible by 4

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Here is what I m using on one of my projects  it s working great and it generates a UNIQUE RANDOM TOKEN    timestampz time     function generateRandomString  length   60         characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ        charactersLength   strlen  characters        randomString           for   i   0   i  lt   length   i               randomString     characters rand 0   charactersLength - 1              return  randomString       tokenparta   generateRandomString       token    timestampz 3    tokenparta   echo  token    Please note that I multiplied the timestamp by three to create a confusion for whoever user  might be wondering how this token is generated     I hope it helps

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Here is ultimate unique id generator for you  made by me    lt  php  d date   d     m date   m     y date   Y     t time     dmt  d  m  y  t       ran  rand 0 10000000    dmtran   dmt  ran   un   uniqid     dmtun    dmt  un   mdun   md5  dmtran  un    sort substr  mdun  16      if you want sort length code   echo  mdun    gt    you can echo any  var  for your id as you like  but  mdun is better  you can replace md5 to sha1 for better code but that will be very long which may you dont need   Thank you

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lt  php function generateRandomString  length   11         characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ        charactersLength   strlen  characters        randomString           for   i   0   i  lt   length   i               randomString     characters rand 0   charactersLength - 1              return  randomString        gt    above function will generate you a random string which is length of 11 characters

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Security Notice  This solution should not be used in situations where the quality of your randomness can affect the security of an application  In particular  rand   and uniqid   are not cryptographically secure random number generators  See Scott s answer for a secure alternative    If you do not need it to be absolutely unique over time   md5 uniqid rand    true    Otherwise  given you have already determined a unique login for your user    md5 uniqid  your user login  true

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I believe the problem with all the existing ideas is that they are probably unique  but not definitely unique  as pointed out in Dariusz Walczak s reply to loletech   I have a solution that actually is unique  It requires that your script have some sort of memory  For me this is a SQL database  You could also simply write to a file somewhere  There are two implementations   First method  have TWO fields rather than 1 that provide uniqueness  The first field is an ID number that is not random but is unique  The first ID is 1  the second 2      If you are using SQL  just define the ID field with the AUTO INCREMENT property  The second field is not unique but is random  This can be generated with any of the other techniques people have already mentioned  Scott s idea was good  but md5 is convenient and probably good enough for most purposes    random token   md5   SERVER  HTTP USER AGENT     time       Second method  Basically the same idea  but initially pick a maximum number of strings that will ever be generated  This could just be a really big number like a trillion  Then do the same thing  generate an ID  but zero pad it so that all IDs are the same number of digits  Then just concatenate the ID with the random string  It will be random enough for most purposes  but the ID section will ensure that it is also unique

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I always use this my function to generate a custom random alphanumeric string    Hope this help    lt  php   function random alphanumeric  length         chars    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ12345689        my string           for   i   0   i  lt   length   i             pos   mt rand 0  strlen  chars  -1          my string    substr  chars   pos  1             return  my string        echo random alphanumeric 50      50 characters   gt    It generates for example  Y1FypdjVbFCFK6Gh9FDJpe6dciwJEfV6MQGpJqAfuijaYSZ86g  If you want compare with another string to be sure that is a unique sequence you can use this trick      string 1   random alphanumeric 50    string 2   random alphanumeric 50   while   string 1     string 2       string 1   random alphanumeric 50      string 2   random alphanumeric 50     if   string 1     string 2         break        echo  string 1  echo   lt br gt  n   echo  string 2    it generate two unique strings   qsBDs4JOoVRfFxyLAOGECYIsWvpcpMzAO9pypwxsqPKeAmYLOi  Ti3kE1WfGgTNxQVXtbNNbhhvvapnaUfGMVJecHkUjHbuCb85pF  Hope this is what you are looking for

[php] PHP: How to generate a random, unique, alphanumeric string for use in a secret link?

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