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Hash1(Hash1(username:realm:password):server_nonce:client_nonce)

client_nonce?

This is how the RFC works: Hash(Hash(username:password):server_nonce)

What is the difference between Hash1 and Hash2?

Hash(username:password) is what you store in the database != plain text.

Also what is realm?

client_nonce?

Yes, the client also generates a nonce that is included in the digest. The full digest (according to RFC 2617) is (assuming qop is used):

request-digest = <"> < KD ( H(A1), unq(nonce-value) ":" nc-value ":" unq(cnonce-value) ":" unq(qop-value) ":" H(A2) ) <">

What is the difference between Hash1 and Hash2?

Hash1 is the hash algorithm for the authorization digest, so MD5 or maybe SHA256 (although only firefox currently supports that). Hash2 is the hash algorithm (including salting) used on the server to hash the hash of the username password before storing in the database.

Hash(username:password) is what you store in the database != plain text.

The password isn't plaintext, but if the Hash(username:password) is compromised that gives an attacker enough information to impersonate that user. The attacker can just use that `Hash(username:password)` to compute the digest, they don't need to know the original password.

Yes, again if the database is compromised, it's compromised... I don't understand why so many people keep mentioning that when HTTPS does not solve that either?!

If a database of passwords is compromised, but the passwords are properly hashed and salted (server-side, not client-side), then you would need a rainbow table for each salt in order to actually get something usable from the compromised data.

Ok, how does HTTPS help with that?

And who cares if you need a rainbow table?

how does HTTPS help with that

Ignoring all the other benefits of HTTPS, it means you can securely transfer the password itself to the server, or a deterministic hash of the password which the server hashes again. Not to mention that you can use a stronger hashing algorithm, like bcrypt. There might be other ways to do this, but https is definitely the most practical.

who cares if you need a rainbow table?

If the passwords are moderately strong and you are using a good hashing algorithm (that is salted), then creating a big enough rainbow table (or brute forcing) is intractable.

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