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this post was submitted on 08 Aug 2025
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Cybersecurity
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The client doesn't confirm the hash. The client hashes and sends the hashed data. The server confirms.
Omg, how do you know my login? ;)
The client doesn't hash. The client needs to send the plain text. Otherwise, that's a security problem; the server needs to confirm the user knows the actual password, so the server needs to compute the hash and compare. If the client sent the hash, then there was no reason to compute hashes in the first place, because the attacker can just send the leaked hash (the reason to hash it is to avoid that the leak can be used to log in directly).
No client side hashing is possible and secure.
If you look at sending plain text under SSL, it's almost the same thing.
The password hashed under a mutually known algorithm that is not reversible is just as good as the plaintext.
What's particularly interesting right now is manipulation of data that is encrypted to allow the same output (encrypted) as unencrypted data.
The point of sending hashes info from the client is that each site uses a different key, even if publicly available. This means that leaked login data cannot be compared or matched across different leaks.
No, it is not. If the server accepts the hash from an untrusted source (the client), then that's equivalent to not using hashes at all. The reason why we hash is so a database leak does not allow malicious actors to login directly. If the server accepts a hash, that means it only does
hash_from_client == hash_from_db, meaning that's the same as doingpassword_from_client == password_from_dbin terms of security. This is because the client can just send the hash from the DB, the user does not actually need to know the password, hence your proposal is equivalent to not using hashes at all in terms of security.That is for keyed hash functions, which is not typically done for passwords (but peppers are sometimes used, which helps similarly). This does not prevent the above scenario, though, because the leaked hash can still be used on that site. Sending hashes is a bad idea, the hash should always be computed in a trusted environment to ensure the user actually knows the password.