path: root/src/m_paper_key/output.cpp

/*
 * Copyright (C) 2007, 2008, 2009, 2012, 2016 David Shaw <[email protected]>
 *
 * This program 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 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include "output.h"

#include <cassert>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#include "packets.h"

extern unsigned int output_width;
extern char *comment;

static enum data_type output_type;
static FILE *output;
static unsigned int line_items;
static unsigned long all_crc = CRC24_INIT;

#define CRC24_POLY 0x864CFBL

void do_crc24(unsigned long *crc, const unsigned char *buf, size_t len) {
  size_t i;

  for (i = 0; i < len; i++) {
    int j;

    *crc ^= buf[i] << 16;
    for (j = 0; j < 8; j++) {
      *crc <<= 1;
      if (*crc & 0x1000000) *crc ^= CRC24_POLY;
    }
  }
}

static void print_base16(const unsigned char *buf, size_t length) {
  static unsigned long line_crc = CRC24_INIT;
  static unsigned int line = 0;

  if (buf) {
    size_t i;
    static unsigned int offset = 0;

    for (i = 0; i < length; i++, offset++) {
      if (offset % line_items == 0) {
        if (line) {
          fprintf(output, "%06lX\n", line_crc & 0xFFFFFFL);
          line_crc = CRC24_INIT;
        }

        fprintf(output, "%3u: ", ++line);
      }

      fprintf(output, "%02X ", buf[i]);

      do_crc24(&line_crc, &buf[i], 1);
    }
  } else {
    fprintf(output, "%06lX\n", line_crc & 0xFFFFFFL);
    fprintf(output, "%3u: %06lX\n", line + 1, all_crc & 0xFFFFFFL);
  }
}

void print_bytes(FILE *stream, const unsigned char *buf, size_t length) {
  size_t i;

  for (i = 0; i < length; i++) fprintf(stream, "%02X", buf[i]);
}

void output_file_format(FILE *stream, const char *prefix) {
  fprintf(stream, "%sFile format:\n", prefix);
  fprintf(stream,
          "%sa) 1 octet:  Version of the paperkey format (currently 0).\n",
          prefix);
  fprintf(stream,
          "%sb) 1 octet:  OpenPGP key or subkey version (currently 4)\n",
          prefix);
  fprintf(stream,
          "%sc) n octets: Key fingerprint (20 octets for a version 4 key or "
          "subkey)\n",
          prefix);
  fprintf(
      stream,
      "%sd) 2 octets: 16-bit big endian length of the following secret data\n",
      prefix);
  fprintf(stream,
          "%se) n octets: Secret data: a partial OpenPGP secret key or subkey "
          "packet as\n",
          prefix);
  fprintf(stream,
          "%s             specified in RFC 4880, starting with the "
          "string-to-key usage\n",
          prefix);
  fprintf(stream,
          "%s             octet and continuing until the end of the packet.\n",
          prefix);
  fprintf(stream,
          "%sRepeat fields b through e as needed to cover all subkeys.\n",
          prefix);
  fprintf(stream, "%s\n", prefix);
  fprintf(
      stream,
      "%sTo recover a secret key without using the paperkey program, use the\n",
      prefix);
  fprintf(stream,
          "%skey fingerprint to match an existing public key packet with the\n",
          prefix);
  fprintf(stream,
          "%scorresponding secret data from the paper key.  Next, append this "
          "secret\n",
          prefix);
  fprintf(stream,
          "%sdata to the public key packet.  Finally, switch the public key "
          "packet tag\n",
          prefix);
  fprintf(stream,
          "%sfrom 6 to 5 (14 to 7 for subkeys).  This will recreate the "
          "original secret\n",
          prefix);
  fprintf(stream,
          "%skey or secret subkey packet.  Repeat as needed for all public key "
          "or subkey\n",
          prefix);
  fprintf(stream,
          "%spackets in the public key.  All other packets (user IDs, "
          "signatures, etc.)\n",
          prefix);
  fprintf(stream, "%smay simply be copied from the public key.\n", prefix);
}

int output_start(FILE *fp, enum data_type type, unsigned char fingerprint[20]) {
  output = fp;
  if (!output) return -1;

  output_type = type;

  switch (type) {
    case RAW:
      break;

    case AUTO:
    case BASE16: {
      time_t now = time(NULL);

      line_items = (output_width - 5 - 6) / 3;
      fprintf(output, "# Secret portions of key ");
      print_bytes(output, fingerprint, 20);
      fprintf(output, "\n");
      fprintf(output, "# Base16 data extracted %.24s\n", ctime(&now));
      fprintf(output,
              "# Created with "
              "Paper Key Module of GpgFrontend"
              " by Saturneric\n#\n");
      output_file_format(output, "# ");
      fprintf(output,
              "#\n# Each base16 line ends with a CRC-24 of that line.\n");
      fprintf(output,
              "# The entire block of data ends with a CRC-24 of the entire "
              "block of data.\n\n");
      // if (comment != nullptr) fprintf(output, "# %s\n\n", comment);
    } break;
  }

  return 0;
}

int output_start(const char *name, enum data_type type,
                 unsigned char fingerprint[20]) {
  if (name) {
    if (type == RAW)
      output = fopen(name, "wb");
    else
      output = fopen(name, "w");

    if (!output) return -1;
  } else {
    if (type == RAW) set_binary_mode(stdout);

    output = stdout;
  }

  output_type = type;

  switch (type) {
    case RAW:
      break;

    case AUTO:
    case BASE16: {
      time_t now = time(NULL);

      line_items = (output_width - 5 - 6) / 3;
      fprintf(output, "# Secret portions of key ");
      print_bytes(output, fingerprint, 20);
      fprintf(output, "\n");
      fprintf(output, "# Base16 data extracted %.24s\n", ctime(&now));
      fprintf(output,
              "# Created with "
              "Paper Key Module of GpgFrontend"
              " by Saturneric\n#\n");
      output_file_format(output, "# ");
      fprintf(output,
              "#\n# Each base16 line ends with a CRC-24 of that line.\n");
      fprintf(output,
              "# The entire block of data ends with a CRC-24 of the entire "
              "block of data.\n\n");
      // if (comment != nullptr) fprintf(output, "# %s\n\n", comment);
    } break;
  }

  return 0;
}

ssize_t output_bytes(const unsigned char *buf, size_t length) {
  ssize_t ret = -1;

  do_crc24(&all_crc, buf, length);

  switch (output_type) {
    case RAW:
      if (buf == NULL) {
        unsigned char crc[3];

        crc[0] = (all_crc & 0xFFFFFFL) >> 16;
        crc[1] = (all_crc & 0xFFFFFFL) >> 8;
        crc[2] = (all_crc & 0xFFFFFFL);

        ret = fwrite(crc, 1, 3, output);
      } else
        ret = fwrite(buf, 1, length, output);
      break;

    case AUTO:
    case BASE16:
      print_base16(buf, length);
      ret = length;
      break;
  }

  return ret;
}

ssize_t output_length16(size_t length) {
  unsigned char encoded[2];

  assert(length <= 65535);

  encoded[0] = length >> 8;
  encoded[1] = length;

  return output_bytes(encoded, 2);
}

ssize_t output_openpgp_header(unsigned char tag, size_t length) {
  unsigned char encoded[6];
  size_t bytes;

  /* We use the same "tag under 16, use old-style packets" rule that
     many OpenPGP programs do.  This helps make the resulting key
     byte-for-byte identical.  It's not a guarantee, as it is legal
     for the generating program to use whatever packet style it likes,
     but does help avoid questions why the input to paperkey might not
     equal the output. */

  if (tag < 16) {
    if (length > 65535) {
      encoded[0] = 0x80 | (tag << 2) | 2;
      encoded[1] = length >> 24;
      encoded[2] = length >> 16;
      encoded[3] = length >> 8;
      encoded[4] = length;
      bytes = 5;
    } else if (length > 255) {
      encoded[0] = 0x80 | (tag << 2) | 1;
      encoded[1] = length >> 8;
      encoded[2] = length;
      bytes = 3;
    } else {
      encoded[0] = 0x80 | (tag << 2);
      encoded[1] = length;
      bytes = 2;
    }
  } else {
    encoded[0] = 0xC0 | tag;

    if (length > 8383) {
      encoded[1] = 0xFF;
      encoded[2] = length >> 24;
      encoded[3] = length >> 16;
      encoded[4] = length >> 8;
      encoded[5] = length;
      bytes = 6;
    } else if (length > 191) {
      encoded[1] = 192 + ((length - 192) >> 8);
      encoded[2] = (length - 192);
      bytes = 3;
    } else {
      encoded[1] = length;
      bytes = 2;
    }
  }

  return output_bytes(encoded, bytes);
}

void output_finish(void) { output_bytes(nullptr, 0); }

void output_end() {
  if (output != nullptr) {
    fflush(output);
    fclose(output);
  }
}

void set_binary_mode(FILE *stream) { (void)stream; }