Re: [android-developers] Re: hash functions

On Wed, May 11, 2011 at 7:34 AM, Bob Kerns <rwk@acm.org> wrote:

> More precisely, you iterate this:
> hash = f(hash)
> where f is some function that is expensive, and does not collapse the space
> of possible values into some smaller set. One way to accomplish this would
> be:
> f(hash) = hash <xor> sha1(hash).
> I went with SHA1 above, because I want to tie this to PBKDF2, which Nikolay
> referenced.

Do you mean you implemented this yourself? Not that it's too hard to do, but
Android has the Bouncy Castle JCE provider, so all you have to do is usually:

SecretKeyFactory factory = SecretKeyFactory.getInstance(KEYGEN_ALGORITHM)
KeySpec keySpec = new PBEKeySpec(password, salt, numInterations, keyLen);
SecretKey key = factory.generateSecret(keySpec);

where KEYGEN_ALGORITHM is a supported PBE algorithm.

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