Data type conversions

[Sergi Blanch i Torné]

I see that, and I can use gcry_mpi_scan() for the other way transformation.

thanks.

/Sergi.

On Fri, Jan 8, 2010 at 2:12 PM, Werner Koch <wk at gnupg.org> wrote:
> On Fri, 8 Jan 2010 11:52:46 +0100, Sergi Blanch i Torné wrote:
>> means, from the point of view of the data, that I have to transform
>> 'gcry_mpi_t' data form/to 'byte*'. In the libgcrypt documentation I
>> didn't find a method for this conversion.
>
> That is easy: Use gcry_mpi_print with a suitable format specifier.
> Have a look at this code in gnupg/g10/build-packet.c:
>
> /*
>  * Write the mpi A to OUT.
>  */
> static int
> mpi_write (iobuf_t out, gcry_mpi_t a)
> {
>  char buffer[(MAX_EXTERN_MPI_BITS+7)/8+2]; /* 2 is for the mpi length. */
>  size_t nbytes;
>  int rc;
>
>  nbytes = DIM(buffer);
>  rc = gcry_mpi_print (GCRYMPI_FMT_PGP, buffer, nbytes, &nbytes, a );
>  if( !rc )
>    rc = iobuf_write( out, buffer, nbytes );
>  else if (gpg_err_code(rc) == GPG_ERR_TOO_SHORT )
>    {
>      log_info ("mpi too large (%u bits)\n", gcry_mpi_get_nbits (a));
>      /* The buffer was too small. We better tell the user about the MPI. */
>      rc = gpg_error (GPG_ERR_TOO_LARGE);
>    }
>
>  return rc;
> }
>
> If you don't want to put an upper limit on the size of the MPI or you
> want to store int in secure memory you need to allocate the buffer.
> gcry_mpi_aprint does this for you and automagically decides whether to
> allocate from the standard or the secure memory pool.  See the gcrypt
> manual.
>
>
> Salam-Shalom,
>
>   Werner
>
> --
> Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.
>
>