Keyed Hash?

[Denys Vlasenko]

On Monday 13 September 2010 21:48, Bryan Dixon wrote:
>   I am currently working on a research project that has need of a keyed 
> hash mechanism, currently we are using a standard hash provided in your 
> current version of busybox. This functionality to pass a phrase as a key 
> to one of the hashing mechanisms (sha1, md5, crc16/crc32) is provided by 
> openssl, which sadly isn't ported to android yet. I didn't know if you 
> have any plans of adding this functionality to your project?

What exactly do you need to achieve?

> I could try and figure out how to do it myself; however, the learning 
> curve would dramatically slow my progress on the larger picture for the 
> research project. I have a few other options but this would be the best 
> solution for what I'm trying to do.

I understood that you want me to do something,
I do not fully understood what exactly.

> An example of what I'd be looking for in context of the openssl command is:
> openssl dgst -sha1 -hmac <"key"> <file>

I am not a crypto guy. Please explain a bit more.

From a quick experiment it looks like w/o "-hmac KEY"
part this command basically does sha1sum'ing.

What does -hmac KEY do? It seeds sha1 somehow? How exactly?

-- 
vda