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I recently found this site, proposing a hashing algorithm for passwords.

They describe the following:

  1. pad the password on both sides with SHA1(email) to 4 * length(password)
  2. HMAC(padded password, global salt)
  3. choose a random salt of 22 characters
  4. bcrypt(hmac, salt)

Is this algorithm secure? I think it might be a security flaw to pad the password on both sides with the same text, and I see no point in using a global salt and a salt which is chosen randomly for every password.

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1 Answer 1

up vote 5 down vote accepted

Points 3 and 4 are a secure way of storing the input to bcrypt (with appropriate choice of parameters for bcrypt).

Points 1 and 2 aren't necessary but don't harm:

  • they would add a small amount of extra computation for an attacker is possession of the password database that wants to do a dictionary attack;
  • the attacker wouldn't be able to straight-out use a standard cracking tool as it is a custom scheme, they would need to modify existing tools or develop their own.
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so it doesn't matter that the sha1(email) is used on both sides of the password? –  pascalhein May 19 '13 at 8:16
    
That's right; provided the password is there in full in the input to HMAC (if HMAC is being used with a standard hash algorithm), adding additional entropy-less data doesn't lower the entropy of the output. –  Michael May 19 '13 at 8:28
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