/* openpgp-oids.c - OID helper for OpenPGP
 * Copyright (C) 2011 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdlib.h>
#include <errno.h>
#include <ctype.h>
#include <assert.h>

#include "util.h"


/* Helper for openpgp_oid_from_str.  */
static size_t
make_flagged_int (unsigned long value, char *buf, size_t buflen)
{
  int more = 0;
  int shift;

  /* fixme: figure out the number of bits in an ulong and start with
     that value as shift (after making it a multiple of 7) a more
     straigtforward implementation is to do it in reverse order using
     a temporary buffer - saves a lot of compares */
  for (more=0, shift=28; shift > 0; shift -= 7)
    {
      if (more || value >= (1<<shift))
        {
          buf[buflen++] = 0x80 | (value >> shift);
          value -= (value >> shift) << shift;
          more = 1;
        }
    }
  buf[buflen++] = value;
  return buflen;
}


/* Convert the OID given in dotted decimal form in STRING to an DER
 * encoding and store it as an opaque value at R_MPI.  The format of
 * the DER encoded is not a regular ASN.1 object but the modified
 * format as used by OpenPGP for the ECC curve description.  On error
 * the function returns and error code an NULL is stored at R_BUG.
 * Note that scanning STRING stops at the first white space
 * character.  */
gpg_error_t
openpgp_oid_from_str (const char *string, gcry_mpi_t *r_mpi)
{
  unsigned char *buf;
  size_t buflen;
  unsigned long val1, val;
  const char *endp;
  int arcno;

  *r_mpi = NULL;

  if (!string || !*string)
    return gpg_error (GPG_ERR_INV_VALUE);

  /* We can safely assume that the encoded OID is shorter than the string. */
  buf = xtrymalloc (1 + strlen (string) + 2);
  if (!buf)
    return gpg_error_from_syserror ();
  /* Save the first byte for the length.  */
  buflen = 1;

  val1 = 0; /* Avoid compiler warning.  */
  arcno = 0;
  do {
    arcno++;
    val = strtoul (string, (char**)&endp, 10);
    if (!digitp (string) || !(*endp == '.' || !*endp))
      {
        xfree (buf);
        return gpg_error (GPG_ERR_INV_OID_STRING);
      }
    if (*endp == '.')
      string = endp+1;

    if (arcno == 1)
      {
        if (val > 2)
          break; /* Not allowed, error catched below.  */
        val1 = val;
      }
    else if (arcno == 2)
      { /* Need to combine the first two arcs in one octet.  */
        if (val1 < 2)
          {
            if (val > 39)
              {
                xfree (buf);
                return gpg_error (GPG_ERR_INV_OID_STRING);
              }
            buf[buflen++] = val1*40 + val;
          }
        else
          {
            val += 80;
            buflen = make_flagged_int (val, buf, buflen);
          }
      }
    else
      {
        buflen = make_flagged_int (val, buf, buflen);
      }
  } while (*endp == '.');

  if (arcno == 1 || buflen < 2 || buflen > 254 )
    { /* It is not possible to encode only the first arc.  */
      xfree (buf);
      return gpg_error (GPG_ERR_INV_OID_STRING);
    }

  *buf = buflen - 1;
  *r_mpi = gcry_mpi_set_opaque (NULL, buf, buflen * 8);
  if (!*r_mpi)
    {
      xfree (buf);
      return gpg_error_from_syserror ();
    }
  return 0;
}


/* Return a malloced string represenation of the OID in the opaque MPI
   A.  In case of an error NULL is returned and ERRNO is set.  */
char *
openpgp_oid_to_str (gcry_mpi_t a)
{
  const unsigned char *buf;
  size_t length;
  unsigned int lengthi;
  char *string, *p;
  int n = 0;
  unsigned long val, valmask;

  valmask = (unsigned long)0xfe << (8 * (sizeof (valmask) - 1));

  if (!a || !gcry_mpi_get_flag (a, GCRYMPI_FLAG_OPAQUE))
    {
      gpg_err_set_errno (EINVAL);
      return NULL;
    }

  buf = gcry_mpi_get_opaque (a, &lengthi);
  length = (lengthi+7)/8;

  /* The first bytes gives the length; check consistency.  */
  if (!length || buf[0] != length -1)
    {
      gpg_err_set_errno (EINVAL);
      return NULL;
    }
  /* Skip length byte.  */
  length--;
  buf++;

  /* To calculate the length of the string we can safely assume an
     upper limit of 3 decimal characters per byte.  Two extra bytes
     account for the special first octect */
  string = p = xtrymalloc (length*(1+3)+2+1);
  if (!string)
    return NULL;
  if (!buf || !length)
    {
      *p = 0;
      return string;
    }

  if (buf[0] < 40)
    p += sprintf (p, "0.%d", buf[n]);
  else if (buf[0] < 80)
    p += sprintf (p, "1.%d", buf[n]-40);
  else {
    val = buf[n] & 0x7f;
    while ( (buf[n]&0x80) && ++n < length )
      {
        if ( (val & valmask) )
          goto badoid;  /* Overflow.  */
        val <<= 7;
        val |= buf[n] & 0x7f;
      }
    val -= 80;
    sprintf (p, "2.%lu", val);
    p += strlen (p);
  }
  for (n++; n < length; n++)
    {
      val = buf[n] & 0x7f;
      while ( (buf[n]&0x80) && ++n < length )
        {
          if ( (val & valmask) )
            goto badoid;  /* Overflow.  */
          val <<= 7;
          val |= buf[n] & 0x7f;
        }
      sprintf (p, ".%lu", val);
      p += strlen (p);
    }

  *p = 0;
  return string;

 badoid:
  /* Return a special OID (gnu.gnupg.badoid) to indicate the error
     case.  The OID is broken and thus we return one which can't do
     any harm.  Formally this does not need to be a bad OID but an OID
     with an arc that can't be represented in a 32 bit word is more
     than likely corrupt.  */
  xfree (string);
  return xtrystrdup ("1.3.6.1.4.1.11591.2.12242973");
}