/*

 * base64.c - support for base64 alphabet system, described in RFC1521

 *

 * This file is part of the SSH Library

 *

 * Copyright (c) 2005-2005 by Aris Adamantiadis

 *

 * The SSH Library is free software; you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation; either version 2.1 of the License, or (at your

 * option) any later version.

 *

 * The SSH Library 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 Lesser General Public

 * License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with the SSH Library; see the file COPYING.  If not, write to

 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,

 * MA 02111-1307, USA.

 */

/* just the dirtiest part of code i ever made */

#include "config.h"

#include <stdio.h>

#include "libssh/priv.h"

#include "libssh/buffer.h"

static char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

                         "abcdefghijklmnopqrstuvwxyz"

                         "0123456789+/";

/* Transformations */

#define SET_A(n, i) do { (n) |= ((i) & 63) <<18; } while (0)

#define SET_B(n, i) do { (n) |= ((i) & 63) <<12; } while (0)

#define SET_C(n, i) do { (n) |= ((i) & 63) << 6; } while (0)

#define SET_D(n, i) do { (n) |= ((i) & 63); } while (0)

#define GET_A(n) (unsigned char) (((n) & 0xff0000) >> 16)

#define GET_B(n) (unsigned char) (((n) & 0xff00) >> 8)

#define GET_C(n) (unsigned char) ((n) & 0xff)

static int _base64_to_bin(unsigned char dest[3], const char *source, int num);

static int get_equals(char *string);

/* First part: base64 to binary */

/**

 * @internal

 *

 * @brief Translates a base64 string into a binary one.

 *

 * @returns A buffer containing the decoded string, NULL if something went

 *          wrong (e.g. incorrect char).

 */

ssh_buffer base64_to_bin(const char *source) {

  ssh_buffer buffer = NULL;

  unsigned char block[3];

  char *base64;

  char *ptr;

  size_t len;

  int equals;

  base64 = strdup(source);

  if (base64 == NULL) {

    return NULL;

  }

  ptr = base64;

  /* Get the number of equals signs, which mirrors the padding */

  equals = get_equals(ptr);

  if (equals > 2) {

    SAFE_FREE(base64);

    return NULL;

  }

  buffer = ssh_buffer_new();

  if (buffer == NULL) {

    SAFE_FREE(base64);

    return NULL;

  }

  /*

   * The base64 buffer often contains sensitive data. Make sure we don't leak

   * sensitive data

   */

  ssh_buffer_set_secure(buffer);

  len = strlen(ptr);

  while (len > 4) {

    if (_base64_to_bin(block, ptr, 3) < 0) {

      goto error;

    }

    if (ssh_buffer_add_data(buffer, block, 3) < 0) {

      goto error;

    }

    len -= 4;

    ptr += 4;

  }

  /*

   * Depending on the number of bytes resting, there are 3 possibilities

   * from the RFC.

   */

  switch (len) {

    /*

     * (1) The final quantum of encoding input is an integral multiple of

     *     24 bits. Here, the final unit of encoded output will be an integral

     *     multiple of 4 characters with no "=" padding

     */

    case 4:

      if (equals != 0) {

        goto error;

      }

      if (_base64_to_bin(block, ptr, 3) < 0) {

        goto error;

      }

      if (ssh_buffer_add_data(buffer, block, 3) < 0) {

        goto error;

      }

      SAFE_FREE(base64);

      return buffer;

    /*

     * (2) The final quantum of encoding input is exactly 8 bits; here, the

     *     final unit of encoded output will be two characters followed by

     *     two "=" padding characters.

     */

    case 2:

      if (equals != 2){

        goto error;

      }

      if (_base64_to_bin(block, ptr, 1) < 0) {

        goto error;

      }

      if (ssh_buffer_add_data(buffer, block, 1) < 0) {

        goto error;

      }

      SAFE_FREE(base64);

      return buffer;

    /*

     * The final quantum of encoding input is exactly 16 bits. Here, the final

     * unit of encoded output will be three characters followed by one "="

     * padding character.

     */

    case 3:

      if (equals != 1) {

        goto error;

      }

      if (_base64_to_bin(block, ptr, 2) < 0) {

        goto error;

      }

      if (ssh_buffer_add_data(buffer,block,2) < 0) {

        goto error;

      }

      SAFE_FREE(base64);

      return buffer;

    default:

      /* 4,3,2 are the only padding size allowed */

      goto error;

  }

error:

  SAFE_FREE(base64);

  ssh_buffer_free(buffer);

  return NULL;

}

#define BLOCK(letter, n) do {ptr = strchr(alphabet, source[n]); \

                             if(!ptr) return -1; \

                             i = ptr - alphabet; \

                             SET_##letter(*block, i); \

                         } while(0)

/* Returns 0 if ok, -1 if not (ie invalid char into the stuff) */

static int to_block4(unsigned long *block, const char *source, int num) {

  char *ptr;

  unsigned int i;

  *block = 0;

  if (num < 1) {

    return 0;

  }

  BLOCK(A, 0); /* 6 bit */

  BLOCK(B,1); /* 12 bit */

  if (num < 2) {

    return 0;

  }

  BLOCK(C, 2); /* 18 bit */

  if (num < 3) {

    return 0;

  }

  BLOCK(D, 3); /* 24 bit */

  return 0;

}

/* num = numbers of final bytes to be decoded */

static int _base64_to_bin(unsigned char dest[3], const char *source, int num) {

  unsigned long block;

  if (to_block4(&block, source, num) < 0) {

    return -1;

  }

  dest[0] = GET_A(block);

  dest[1] = GET_B(block);

  dest[2] = GET_C(block);

  return 0;

}

/* Count the number of "=" signs and replace them by zeroes */

static int get_equals(char *string) {

  char *ptr = string;

  int num = 0;

  while ((ptr=strchr(ptr,'=')) != NULL) {

    num++;

    *ptr = '\0';

    ptr++;

  }

  return num;

}

/* thanks sysk for debugging my mess :) */

#define BITS(n) ((1 << (n)) - 1)

static void _bin_to_base64(unsigned char *dest, const unsigned char source[3],

    int len) {

  switch (len) {

    case 1:

      dest[0] = alphabet[(source[0] >> 2)];

      dest[1] = alphabet[((source[0] & BITS(2)) << 4)];

      dest[2] = '=';

      dest[3] = '=';

      break;

    case 2:

      dest[0] = alphabet[source[0] >> 2];

      dest[1] = alphabet[(source[1] >> 4) | ((source[0] & BITS(2)) << 4)];

      dest[2] = alphabet[(source[1] & BITS(4)) << 2];

      dest[3] = '=';

      break;

    case 3:

      dest[0] = alphabet[(source[0] >> 2)];

      dest[1] = alphabet[(source[1] >> 4) | ((source[0] & BITS(2)) << 4)];

      dest[2] = alphabet[ (source[2] >> 6) | (source[1] & BITS(4)) << 2];

      dest[3] = alphabet[source[2] & BITS(6)];

      break;

  }

}

/**

 * @internal

 *

 * @brief Converts binary data to a base64 string.

 *

 * @returns the converted string

 */

unsigned char *bin_to_base64(const unsigned char *source, int len) {

  unsigned char *base64;

  unsigned char *ptr;

  int flen = len + (3 - (len % 3)); /* round to upper 3 multiple */

  flen = (4 * flen) / 3 + 1;

  base64 = malloc(flen);

  if (base64 == NULL) {

    return NULL;

  }

  ptr = base64;

  while(len > 0){

    _bin_to_base64(ptr, source, len > 3 ? 3 : len);

    ptr += 4;

    source += 3;

    len -= 3;

  }

  ptr[0] = '\0';

  return base64;

}