Does server stores my previos passwords?












2














When I change my password on some web server like email, cloud, social network and try to use my previous password, server denied it with message "Don't use your previous passwords".
- Does it mean that server stores my my previous passwords? How does it secure?






passwords







share|improve this question



























    2














    When I change my password on some web server like email, cloud, social network and try to use my previous password, server denied it with message "Don't use your previous passwords".
    - Does it mean that server stores my my previous passwords? How does it secure?






    passwords







    share|improve this question

























      2












      2








      2







      When I change my password on some web server like email, cloud, social network and try to use my previous password, server denied it with message "Don't use your previous passwords".
      - Does it mean that server stores my my previous passwords? How does it secure?






      passwords







      share|improve this question













      When I change my password on some web server like email, cloud, social network and try to use my previous password, server denied it with message "Don't use your previous passwords".
      - Does it mean that server stores my my previous passwords? How does it secure?






      passwords




      passwords






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked 3 hours ago









      sluge

      406144




      406144






















          1 Answer
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          Hash functions deterministic functions, same input results always the same output. They can store the previous hash values of your old passwords and compare them with your new proposed password's hash. To achieve this, they also need to store at least the salt values, too. This means the salt and other parameters has to be the same for you in this site.



          From here, without the server side code, we cannot say more than like this.






          share|improve this answer



















          • 1




            Especially if salt is a user name or user's email.
            – sluge
            2 hours ago










          • Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
            – Federico Poloni
            15 mins ago








          • 1




            Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
            – Federico Poloni
            12 mins ago











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          1 Answer
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          1 Answer
          1






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          active

          oldest

          votes






          active

          oldest

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          3














          Hash functions deterministic functions, same input results always the same output. They can store the previous hash values of your old passwords and compare them with your new proposed password's hash. To achieve this, they also need to store at least the salt values, too. This means the salt and other parameters has to be the same for you in this site.



          From here, without the server side code, we cannot say more than like this.






          share|improve this answer



















          • 1




            Especially if salt is a user name or user's email.
            – sluge
            2 hours ago










          • Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
            – Federico Poloni
            15 mins ago








          • 1




            Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
            – Federico Poloni
            12 mins ago
















          3














          Hash functions deterministic functions, same input results always the same output. They can store the previous hash values of your old passwords and compare them with your new proposed password's hash. To achieve this, they also need to store at least the salt values, too. This means the salt and other parameters has to be the same for you in this site.



          From here, without the server side code, we cannot say more than like this.






          share|improve this answer



















          • 1




            Especially if salt is a user name or user's email.
            – sluge
            2 hours ago










          • Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
            – Federico Poloni
            15 mins ago








          • 1




            Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
            – Federico Poloni
            12 mins ago














          3












          3








          3






          Hash functions deterministic functions, same input results always the same output. They can store the previous hash values of your old passwords and compare them with your new proposed password's hash. To achieve this, they also need to store at least the salt values, too. This means the salt and other parameters has to be the same for you in this site.



          From here, without the server side code, we cannot say more than like this.






          share|improve this answer














          Hash functions deterministic functions, same input results always the same output. They can store the previous hash values of your old passwords and compare them with your new proposed password's hash. To achieve this, they also need to store at least the salt values, too. This means the salt and other parameters has to be the same for you in this site.



          From here, without the server side code, we cannot say more than like this.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 2 hours ago

























          answered 3 hours ago









          kelalaka

          6351615




          6351615








          • 1




            Especially if salt is a user name or user's email.
            – sluge
            2 hours ago










          • Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
            – Federico Poloni
            15 mins ago








          • 1




            Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
            – Federico Poloni
            12 mins ago














          • 1




            Especially if salt is a user name or user's email.
            – sluge
            2 hours ago










          • Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
            – Federico Poloni
            15 mins ago








          • 1




            Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
            – Federico Poloni
            12 mins ago








          1




          1




          Especially if salt is a user name or user's email.
          – sluge
          2 hours ago




          Especially if salt is a user name or user's email.
          – sluge
          2 hours ago












          Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
          – Federico Poloni
          15 mins ago






          Don't they need to store the salt value anyway to authenticate you? Basically, if the server had enough information to run a function is_password_correct() earlier (and it needed to, to log you in), then it can still save all the information required to run it after you have changed your password.
          – Federico Poloni
          15 mins ago






          1




          1




          Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
          – Federico Poloni
          12 mins ago




          Also, note that if the server answers "your new password is too similar to the password you had 1 month ago" instead, then it means that they have stored it in plain text, or that they have done something almost as insecure as storing it in plain text. Run, don't walk.
          – Federico Poloni
          12 mins ago


















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