SHA1 - set initial key/state?

[NickAsh]

Hi Folks,

I may be missing something in my use of the SHA1 algorithm, I am
hoping you can explain it to me.

I have an unencrypted string, I make a function call like:
my_sha1_object.calculateDigest(outputdigest, inputstring, length);

No problems there, my digest is created.


However, I am sending this information across a socket, so I'm
thinking that anyone can snoop my unencrypted string,
and assuming they were also using cryptopp sha algorithm, they would
easily be able to recreate the same digest.

Am I wrong in thinking this is insecure - am I thinking about this
incorrectly?

I've been wondering if there is some way to initialise the "state" of
the sha object with our own key/values, which would be secure, and
unrepeatable.

I have looked in to the sha1.InitState function - this retrieves the
intial state - but how do you set it?

Is the "transform" function what I am after? There is no documentation/
usage guide/examples or even comments (or my google-fu is weak!) for
either InitState or Transform functions.
So, what are they for, and do they do what I want?

thanks!

Nick Aschberger
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[Jeffrey Walton-3]

Hi Nick,

Use an HMAC.

Jeff

On 6/25/09, Nick Aschberger <nick.aschberger@...> wrote:

>
>  Hi Folks,
>
>  I may be missing something in my use of the SHA1 algorithm, I am
>  hoping you can explain it to me.
>
>  I have an unencrypted string, I make a function call like:
>  my_sha1_object.calculateDigest(outputdigest, inputstring, length);
>
>  No problems there, my digest is created.
>
>
>  However, I am sending this information across a socket, so I'm
>  thinking that anyone can snoop my unencrypted string,
>  and assuming they were also using cryptopp sha algorithm, they would
>  easily be able to recreate the same digest.
>
>  Am I wrong in thinking this is insecure - am I thinking about this
>  incorrectly?
>
>  I've been wondering if there is some way to initialise the "state" of
>  the sha object with our own key/values, which would be secure, and
>  unrepeatable.
>
>  I have looked in to the sha1.InitState function - this retrieves the
>  intial state - but how do you set it?
>
>  Is the "transform" function what I am after? There is no documentation/
>  usage guide/examples or even comments (or my google-fu is weak!) for
>  either InitState or Transform functions.
>  So, what are they for, and do they do what I want?
>
>  thanks!
>
>
>  Nick Aschberger
>

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[NickAsh]

Oh.... duh. It's so simple!

Thanks Jeff.

On Jun 25, 4:29 pm, Jeffrey Walton <noloa...@...> wrote:

> Hi Nick,
>
> Use an HMAC.
>
> Jeff
>
> On 6/25/09, Nick Aschberger <nick.aschber...@...> wrote:
>
>
>
> >  Hi Folks,
>
> >  I may be missing something in my use of the SHA1 algorithm, I am
> >  hoping you can explain it to me.
>
> >  I have an unencrypted string, I make a function call like:
> >  my_sha1_object.calculateDigest(outputdigest, inputstring, length);
>
> >  No problems there, my digest is created.
>
> >  However, I am sending this information across a socket, so I'm
> >  thinking that anyone can snoop my unencrypted string,
> >  and assuming they were also using cryptopp sha algorithm, they would
> >  easily be able to recreate the same digest.
>
> >  Am I wrong in thinking this is insecure - am I thinking about this
> >  incorrectly?
>
> >  I've been wondering if there is some way to initialise the "state" of
> >  the sha object with our own key/values, which would be secure, and
> >  unrepeatable.
>
> >  I have looked in to the sha1.InitState function - this retrieves the
> >  intial state - but how do you set it?
>
> >  Is the "transform" function what I am after? There is no documentation/
> >  usage guide/examples or even comments (or my google-fu is weak!) for
> >  either InitState or Transform functions.
> >  So, what are they for, and do they do what I want?
>
> >  thanks!
>
> >  Nick Aschberger

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