Error encrypting string data

Werner Koch
Fri, 18 Jul 2003 13:20:24 +0200

On Thu, 17 Jul 2003 13:37:25 +0200, Ralf Schneider said:

>   x = gcry_mpi_new (0);
>   gcry_mpi_set_opaque (x, text, strlen(text));

You can't use opaque becuase that won't yield a valid MPI which can be
passed to other MPI functions.  Opaque is a hack to allow for
encrypted MPI values.

To convert a string into an MPI, use this:

   gcry_mpi_t a;
   int rc;
   const char string[] = "Is that all you've got to show for seven "
                         "and a half million years' work?";

   rc = gcry_mpi_scan (&a, GCRYMPI_FMT_USG, string, strlen (string));
   if (rc)
      bug ("oops: mpi_scan failed: %s\n", gpg_strerror (rc));

   foo (a)
   gcry_mpi_release (a);

However, using this is not secure as proper padding is required for
most public key algorithms; see the HAC for details.



Werner Koch                                      <>
The GnuPG Experts                      
Free Software Foundation Europe