I know that we cannot update our hashed passwords without having the plain text password to re-hash. When a member logs in with login/password, we have the plain text, so that gives us an opportunity to more securely hash and store the member password.

Does anyone have experience with asking your members to "please come to our site and log in with your real password" without causing mass panic? Any way that I can think of to convey the request sounds like we have had a data breach. We are simply looking at ways to upgrade our security, and Ashley Madison makes it clear that hashed passwords are a point to carefully consider.


I don't see a reason why it should be problematic to take the existing hashes, take them as input for a more secure hash function and migrate all existing users at once. Extensive discussion on the approach can be found here. You will have to store both old and new salts, of course.

In combination with a good password policy (force your users to change passwords after a reasonable period) you can slowly phase out the 'legacy' passwords.

  • thank you for the link. That lets us take an immediate step while letting "policy" changes run their course. Sep 15 '15 at 18:51

Tell your userbase that you guys are upgrading your security and as a result you will need them to change their passwords. Or you could allow them to be migrated over a period of time as users passwords expire if you are using good password policies.

  • Simple and to the point, therefore very likely the best answer for our situation. Forcing an expiration or reset-required is also feasible for us. Sep 15 '15 at 18:43
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    There is another reason this is a good idea. The fact that you are changing your password policy suggests that the old way is not as secure, and therefore all of the existing passwords are more likely to be compromised, so asking them to change their passwords makes sense.
    – TTT
    Sep 15 '15 at 20:29

Since you've changed your password storing policy lets say, you can send a notification to users to update their password but you will have to have a way to keep the old passwords for those who are unwilling to change.

let me give an example to make it clear : lets say I'm currently saving plain hash of users passwords and Im going to add a random salt and also use pbkdf2 with 1000 rounds, I'll save passwords like this: [Number of rounds password is hashed]:[salt]:[password hash]

so old users password will look like this:


and for new users Ill save a hash and number of pbkdf2 rounds used, so this way I'll have a backward compatible way to handle users passwords.

btw, new password will look like this:

1000:random salt:hash

  • You have nailed the problem: users who are unwilling to change. Without disclosing what we DO support, I do think re-thinking our policies and conveying that to our customers is a good part of the solution. With the spectacular Target, Ashley Madison, LinkedIn, etc., breaches, it's my hope that more assertive policies can be accepted. No way will we have 100% acceptance, of course. Sep 15 '15 at 18:56

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