best practice to generate random token for forgot password

Question

I want to generate identifier for forgot password   I read i can do it by using timestamp with   mt rand    but some people are saying that time stamp might not be unique every time  So i am bit of confused here  Can i do it with using time stamp with this    Question What s best practice to generate random unique tokens of custom length   I know there are lot of questions asked around here but i am getting more confused after reading different opinion from the different people

User · Accepted Answer

In PHP  use random bytes    Reason  your are seeking the way to get a password reminder token  and  if it is a one-time login credentials  then you actually have a data to protect  which is - whole user account   So  the code will be as follows      length   78 etc  token   bin2hex random bytes  length        Update  previous versions of this answer was referring to uniqid   and that is incorrect if there is a matter of security and not only uniqueness  uniqid   is essentially just microtime   with some encoding  There are simple ways to get accurate predictions of the microtime   on your server  An attacker can issue a password reset request and then try through a couple of likely tokens  This is also possible if more entropy is used  as the additional entropy is similarly weak  Thanks to  NikiC and  ScottArciszewski for pointing this out   For more details see    http   phpsecurity readthedocs org en latest Insufficient-Entropy-For-Random-Values html

User · Answer

This answers the  best random  request  Adi s answer1 from Security StackExchange has a solution for this   Make sure you have OpenSSL support  and you ll never go wrong with this one-liner  token   bin2hex openssl random pseudo bytes 16       1  Adi  Mon Nov 12 2018  Celeritas   quot Generating an unguessable token for confirmation e-mails quot   Sep 20  13 at 7 06  https   security stackexchange com a 40314

User · Answer

This may be helpful whenever you need a very very random token   lt  php    echo mb strtoupper strval bin2hex openssl random pseudo bytes 16        gt

User · Answer

You can also use DEV RANDOM  where 128   1 2 the generated token length  Code below generates 256 token    token   bin2hex mcrypt create iv 128  MCRYPT DEV RANDOM

User · Answer

The earlier version of the accepted answer  md5 uniqid mt rand    true    is insecure and only offers about 2 60 possible outputs -- well within the range of a brute force search in about a week s time for a low-budget attacker    mt rand   is predictable  and only adds up to 31 bits of entropy  uniqid   only adds up to 29 bits of entropy md5   doesn t add entropy  it just mixes it deterministically   Since a 56-bit DES key can be brute-forced in about 24 hours  and an average case would have about 59 bits of entropy  we can calculate 2 59   2 56   about 8 days  Depending on how this token verification is implemented  it might be possible to practically leak timing information and infer the first N bytes of a valid reset token   Since the question is about  best practices  and opens with        I want to generate identifier for forgot password      we can infer that this token has implicit security requirements  And when you add security requirements to a random number generator  the best practice is to always use a cryptographically secure pseudorandom number generator  abbreviated CSPRNG      Using a CSPRNG  In PHP 7  you can use bin2hex random bytes  n    where  n is an integer larger than 15     In PHP 5  you can use random compat to expose the same API    Alternatively  bin2hex mcrypt create iv  n  MCRYPT DEV URANDOM   if you have ext mcrypt installed  Another good one-liner is bin2hex openssl random pseudo bytes  n     Separating the Lookup from the Validator  Pulling from my previous work on secure  remember me  cookies in PHP  the only effective way to mitigate the aforementioned timing leak  typically introduced by the database query  is to separate the lookup from the validation   If your table looks like this  MySQL      CREATE TABLE account recovery       id INTEGER 11  UNSIGNED NOT NULL AUTO INCREMENT      userid INTEGER 11  UNSIGNED NOT NULL      token CHAR 64       expires DATETIME      PRIMARY KEY id           you need to add one more column  selector  like so   CREATE TABLE account recovery       id INTEGER 11  UNSIGNED NOT NULL AUTO INCREMENT      userid INTEGER 11  UNSIGNED NOT NULL      selector CHAR 16       token CHAR 64       expires DATETIME      PRIMARY KEY id       KEY selector       Use a CSPRNG When a password reset token is issued  send both values to the user  store the selector and a SHA-256 hash of the random token in the database  Use the selector to grab the hash and User ID  calculate the SHA-256 hash of the token the user provides with the one stored in the database using hash equals     Example Code  Generating a reset token in PHP 7  or 5 6 with random compat  with PDO    selector   bin2hex random bytes 8     token   random bytes 32     urlToEmail    http   example com reset php   http build query        selector    gt   selector       validator    gt  bin2hex  token        expires   new DateTime  NOW     expires- gt add new DateInterval  PT01H        1 hour   stmt    pdo- gt prepare  INSERT INTO account recovery  userid  selector  token  expires  VALUES   userid   selector   token   expires       stmt- gt execute        userid    gt   userId     define this elsewhere       selector    gt   selector       token    gt  hash  sha256    token        expires    gt   expires- gt format  Y-m-d TH i s         Verifying the user-provided reset token    stmt    pdo- gt prepare  SELECT   FROM account recovery WHERE selector     AND expires  gt   NOW       stmt- gt execute   selector     results    stmt- gt fetchAll PDO  FETCH ASSOC   if   empty  results          calc   hash  sha256   hex2bin  validator        if  hash equals  calc   results 0   token                  The reset token is valid  Authenticate the user               Remove the token from the DB regardless of success or failure      These code snippets are not complete solutions  I eschewed the input validation and framework integrations   but they should serve as an example of what to do

[php] best practice to generate random token for forgot password

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