[openssl-dev] Variable length of digest

[Dmitry Belyavsky]

Dear Victor,

On Thu, Dec 24, 2015 at 11:02 AM, Victor Wagner <vitus at wagner.pp.ru> wrote:

> On Thu, 24 Dec 2015 10:45:37 +0300
> Dmitry Belyavsky <beldmit at gmail.com> wrote:
>
>
> > >
> > > If there's a new construct whose output size depends on the input
> > > data, that probably requires a new family of functions.
> > >
> >
> > Well, the gost-mac is treated specially itself and may be it can be
> > simplified introducing the new construction.
>
> Really it is MAC. I.e. it is combination of digest and pkey algorithms,
> and digest itself is never seen by any application. Applications only
> access MAC value via EVP_DigestSignFinal  interface. And it already
> allows variable size of signature.
>

If you try to change the output length via the -macopt option of the dgst
command, you'll see that the text output will be 4 bytes.
It seems to happen because of the internal call to the EVP_MD_size()
function.

If we change the EVP_MD_CTX_size() definition from a macro to a function
trying to call the ctrl function and then to fallback to the result of the
EVP_MD_size() function, it should improve the situation.

-- 
SY, Dmitry Belyavsky
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