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> each subsequent time a user logs in you have to hash the password twice with two different hashing schemes The first time such a user logs in, you can upgrad

> each subsequent time a user logs in you have to hash the password twice with two different hashing schemes The first time such a user logs in, you can upgrade their hash to the latest scheme, so there's no extra work on later logins. Django, e.g., does just this, automatically. https://docs.djangoproject.com/en/1.10/topics/auth/passwords/#password-upgrading https://docs.djangoproject.com/en/1.10/topics/auth/passwords...

Svenskunganka 10y ago
That's exactly what I was implying...
- medmunds 10y ago
  Sorry, I was trying to point out that you can have it both ways. As pixelcort suggested, do a one-time upgrade of all (weak) hashes to newScheme(oldScheme(password). But then as users login, you can upgrade them to just newScheme(password). No need to force a reset just because people haven't logged in recently. I'm familiar with Django, and they happen to have some nice docs on both parts of the process: bulk upgrade to stronger scheme by wrapping [1] and individual upgrade on login [2]. But the technique isn't unique to Django. [1]: https://docs.djangoproject.com/en/1.10/topics/auth/passwords/#password-upgrading-without-requiring-a-login https://docs.djangoproject.com/en/1.10/topics/auth/passwords... [2]: https://docs.djangoproject.com/en/1.10/topics/auth/passwords/#password-upgrading https://docs.djangoproject.com/en/1.10/topics/auth/passwords...
  - Svenskunganka 10y ago
    Alright, I understand now. A bit hard to figure that out from your original comment though, but thank you for clarifying! I'm curious about using two different algorithms for hashing at the same time would affect entropy. It could be that the original plain-text password has better entropy than the SHA1 hash (if that was your old hashing scheme) of the original password has.
    - StavrosK 10y ago
      It might, but nobody is going to discover your password by brute-forcing the SHA1 digest result.

Svenskunganka 10y ago

That's exactly what I was implying...

medmunds 10y ago
Sorry, I was trying to point out that you can have it both ways. As pixelcort suggested, do a one-time upgrade of all (weak) hashes to newScheme(oldScheme(password). But then as users login, you can upgrade them to just newScheme(password). No need to force a reset just because people haven't logged in recently. I'm familiar with Django, and they happen to have some nice docs on both parts of the process: bulk upgrade to stronger scheme by wrapping [1] and individual upgrade on login [2]. But the technique isn't unique to Django. [1]: https://docs.djangoproject.com/en/1.10/topics/auth/passwords/#password-upgrading-without-requiring-a-login https://docs.djangoproject.com/en/1.10/topics/auth/passwords... [2]: https://docs.djangoproject.com/en/1.10/topics/auth/passwords/#password-upgrading https://docs.djangoproject.com/en/1.10/topics/auth/passwords...
- Svenskunganka 10y ago
  Alright, I understand now. A bit hard to figure that out from your original comment though, but thank you for clarifying! I'm curious about using two different algorithms for hashing at the same time would affect entropy. It could be that the original plain-text password has better entropy than the SHA1 hash (if that was your old hashing scheme) of the original password has.
  - StavrosK 10y ago
    It might, but nobody is going to discover your password by brute-forcing the SHA1 digest result.