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POIs MD5 still considered secure for single use authentications?
 

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  1. POIs MD5 still considered secure for single use authentications?
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    <p>Everyone is shooting down MD5 these days for its issues in the context of storing passwords. But what about uses where I just want to add a layer of authentication to something that will likely be used once?</p> <p>This is just a hypothetical example, but let's say I have a feature to allow a user to reset their password. I email the user a link that they can click to set a new (randomly-generated) password.</p> <p>My current thinking is that I'll generate an MD5 hash, using a private salt value, and a couple of identifying variables, and use that to create the link.</p> <p>Let's say the salt for this feature is "8b769a378411b705" (I use the same salt for all reset password requests). The other identifying pieces of data are the user ID and a database ID of the already-generated password hashes.</p> <pre><code>salt = "8b769a378411b705" (private) user_id = 123 pw_id = 456 code = md5(salt + " " + user_id + " " + pw_id) </code></pre> <p>which becomes</p> <pre><code>code = "692a71cd7da194145be209e40fcd3e92" </code></pre> <p>example link: <strong>confirm_reset_password.php?user_id=123&amp;pw_id=456&amp;code=692a71cd7da194145be209e40fcd3e92</strong></p> <p>Is this considered safe, in light of the issues with MD5? Is there another one-way hash I should consider using, like SHA-1?</p> <p>I've been using PBKDF2 with SHA1 for storing passwords, and I understand that part of its benefit is in its "slowness" and how long it takes to generate hashes. I could generate those higher-quality hashes for purposes like this, but I think it can backfire, since you could easily bring a server to its knees by bombarding it with (incorrect) requests, since each one results in a significant CPU job to generate the hash (especially since I am using lots of iterations). It seems that having a "fast" algorithm is good for single use purposes, but I'm wondering if MD5 is still the best choice.</p> <p>Thanks!</p>
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    1. USDivideByHero
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    1. COIn my opinion md5 is acceptable. The problem why many people avoid using md5 is because this storing method has been standard for a long time. thus there are giant list of md5 hashes with the matching password out there. this way you can decrypt most of the passwords in a second.
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      1. POIs MD5 still considered secure for single use authentications?
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    2. COi meant acceptable in your example, for a one time use
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