I am hoping someone might shed some light on which library I might use if any are available to convert a PHP based application that has been using BCrypt $2a to a .Net based application, the current BCrypt C# Library I used I just realized is using $2y so I will not be able to seemlessly migrate users without causing mass password resets. Is there a $2a port to C# that is available or the inverse a $2y implementation in PHP that I might retro fit into the existing system and re-hash passwords. Ideally I would like to do zero coding in the PHP version and be able to migrate to .Net platform.
Thank you.
As for $2a$, it depends on how old your version of PHP bcrypt is.
Pre-2011, you will want to change $2a$ to $2x$. Post-2011, $2a$ and $2y$ are (except for sequences of 0xff which can't be produced by UTF-8 passwords) equivalent. All three are equivalent for ASCII passwords.
My library CryptSharp can do bcrypt in $2a$ (post-2011, $2y$ equivalent), $2x$, and $2y$ form.