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Comment by pjscott | Hacker News Reader

Bcrypt uses Blowfish, but it is not Blowfish.

Sorry, I didn't think my last comment needed clarifying any further - I actively use the bcrypt class for password hashing - I said Blowfish originally as I was comparing hashing algorithms.

Blowfish is a block cipher, not a hashing algorithm.

I'm no expert, but [1] says:

> bcrypt is an adaptive password hashing algorithm

[1]: http://codahale.com/how-to-safely-store-a-password/

Bcrypt is an adaptive password hashing algorithm. Blowfish is a block cipher.

Most encryption algorithms (including block ciphers) can be used as a hashing algorithm for passwords.

Just encrypt a common known plaintext string and use the password as the encryption key. This is exactly how various hashing schemes like UNIX's crypt() (based on DES) work.

Knowing the plaintext (e.g. a set of NUL bytes) is useless as long as the encryption scheme doesn't have a weakness against known-plaintext attacks [EDIT] that allow you to recover the encryption key somehow.

Yes, and Blowfish (or rather, a variant of it with an expensive key schedule) is used as the main building block of Bcrypt in roughly the way you describe. That doesn't mean that Blowfish is Bcrypt.

I feel like such a pedantic dick for harping on this, but the distinction is worth making.

Encryption does not provide Integrity (hash) or authentication (mac)

crypt(1) should be an example of how not to do hashing.

Perfectly true, but those points are irrelevant for password hashing.

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