[Cryptography] Key stretching

William Allen Simpson william.allen.simpson at gmail.com
Fri Oct 11 23:55:12 EDT 2013


On 10/11/13 7:34 PM, Peter Gutmann wrote:
> Phillip Hallam-Baker <hallam at gmail.com> writes:
>
>> Quick question, anyone got a good scheme for key stretching?
>
> http://lmgtfy.com/?q=hkdf&l=1
>
Yeah, that's a weaker simplification of the method I've always
advocated, stopping the hash function before the final
MD-strengthing and repeating the input, only doing the
MD-strengthening for the last step for each key.  I used this in
many of my specifications.

In essence, the MD-strengthening counter is the same as the 0xnn
counter they used, although longer and stronger.

This assures there are no releated key attacks, as the internal
chaining variables aren't exposed.



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