expanding a password into many keys

[Ondrej Mikle]

On 6/12/05, Ian G <iang at systemics.com> wrote:
> I'd like to take a password and expand it into
> several keys.  It seems like a fairly simple operation
> of hashing the concatonatonation of the password
> with each key name in turn to get each key.
> 
> Are there any 'gotchas' with that?
> 
> iang
> 

I guess you should use some scheme like PKCS #5 PBKDF2 scheme
(password based key derivation function). The only difference between
your idea and PBKDF2 is that the latter does a lot of hash rounds and
is salted (I guess you pick key name to be static and not random, so
they are not used as salts).
Salting helps a bit against static precomputed hashes and techniques
like rainbow tables.

Ondrej Mikle

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