pgp-encode.c

/* pgp.c
 *
 * PGP related functions.
 */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2001, 2002 Niels Mller
 *  
 * The nettle 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 nettle 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 nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>
#include <stdlib.h>
#include <string.h>

#if HAVE_LIBGMP
# include "bignum.h"
# include "pgp.h"
#else /* !HAVE_LIBGMP */
/* Kludge to make it possible to include pgp.h */
# define mpz_t int
# include "pgp.h"
# undef mpz_t
#endif /* !HAVE_LIBGMP */

#if WITH_PUBLIC_KEY
# include "rsa.h"
#endif

#include "base64.h"
#include "buffer.h"
#include "macros.h"

int
pgp_put_uint32(struct nettle_buffer *buffer, uint32_t i)
{
  uint8_t *p = nettle_buffer_space(buffer, 4);
  if (!p)
    return 0;
  
  WRITE_UINT32(p, i);
  return 1;
}

int
pgp_put_uint16(struct nettle_buffer *buffer, unsigned i)
{
  uint8_t *p = nettle_buffer_space(buffer, 2);
  if (!p)
    return 0;
  
  WRITE_UINT16(p, i);
  return 1;
}

#if HAVE_LIBGMP
int
pgp_put_mpi(struct nettle_buffer *buffer, const mpz_t x)
{
  unsigned bits = mpz_sizeinbase(x, 2);
  unsigned octets = (bits + 7) / 8;

  uint8_t *p;

  /* FIXME: What's the correct representation of zero? */
  if (!pgp_put_uint16(buffer, bits))
    return 0;
  
  p = nettle_buffer_space(buffer, octets);

  if (!p)
    return 0;
  
  nettle_mpz_get_str_256(octets, p, x);

  return 1;
}
#endif

int
pgp_put_string(struct nettle_buffer *buffer,
	       unsigned length,
	       const uint8_t *s)
{
  return nettle_buffer_write(buffer, length, s);
}

#if 0
static unsigned
length_field(unsigned length)
{
  if (length < PGP_LENGTH_TWO_OCTET)
    return 1;
  else if (length < PGP_LENGTH_FOUR_OCTETS)
    return 2;
  else return 4;
}
#endif

/*   bodyLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192
 *   ==> bodyLen - 192 + 192 << 8 = (1st_octet << 8) + (2nd_octet) 
 */

#define LENGTH_TWO_OFFSET (192 * 255)

int
pgp_put_length(struct nettle_buffer *buffer,
	       unsigned length)
{
  if (length < PGP_LENGTH_TWO_OCTETS)
    return NETTLE_BUFFER_PUTC(buffer, length);

  else if (length < PGP_LENGTH_FOUR_OCTETS)
    return pgp_put_uint16(buffer, length + LENGTH_TWO_OFFSET);
  else
    return NETTLE_BUFFER_PUTC(buffer, 0xff) && pgp_put_uint32(buffer, length);
}

/* Uses the "new" packet format */
int
pgp_put_header(struct nettle_buffer *buffer,
	       unsigned tag, unsigned length)
{
  assert(tag < 0x40);

  return (NETTLE_BUFFER_PUTC(buffer, 0xC0 | tag)
	  && pgp_put_length(buffer, length));  
}

/* FIXME: Should we abort or return error if the length and the field
 * size don't match? */
void
pgp_put_header_length(struct nettle_buffer *buffer,
		      /* start of the header */
		      unsigned start,
		      unsigned field_size)
{
  unsigned length;
  switch (field_size)
    {
    case 1:
      length = buffer->size - (start + 2);
      assert(length < PGP_LENGTH_TWO_OCTETS);
      buffer->contents[start + 1] = length;
      break;
    case 2:
      length = buffer->size - (start + 3);
      assert(length < PGP_LENGTH_FOUR_OCTETS
	     && length >= PGP_LENGTH_TWO_OCTETS);
      WRITE_UINT16(buffer->contents + start + 1, length + LENGTH_TWO_OFFSET);
      break;
    case 4:
      length = buffer->size - (start + 5);
      WRITE_UINT32(buffer->contents + start + 2, length);
      break;
    default:
      abort();
    }
}

int
pgp_put_userid(struct nettle_buffer *buffer,
	       unsigned length,
	       const uint8_t *name)
{
  return (pgp_put_header(buffer, PGP_TAG_USERID, length)
	  && pgp_put_string(buffer, length, name));
}

unsigned
pgp_sub_packet_start(struct nettle_buffer *buffer)
{
  return nettle_buffer_space(buffer, 2) ? buffer->size : 0;
}

int
pgp_put_sub_packet(struct nettle_buffer *buffer,
		   unsigned type,
		   unsigned length,
		   const uint8_t *data)
{
  return (pgp_put_length(buffer, length + 1)
	  && NETTLE_BUFFER_PUTC(buffer, type)
	  && pgp_put_string(buffer, length, data));
}

void
pgp_sub_packet_end(struct nettle_buffer *buffer, unsigned start)
{
  unsigned length;
  
  assert(start >= 2);
  assert(start <= buffer->size);

  length = buffer->size - start;
  WRITE_UINT32(buffer->contents + start - 2, length);
}

#if WITH_PUBLIC_KEY
int
pgp_put_public_rsa_key(struct nettle_buffer *buffer,
		       const struct rsa_public_key *pub,
		       time_t timestamp)
{
  /* Public key packet, version 4 */
  unsigned start;
  unsigned length;

  /* Size of packet is 16 + the size of e and n */
  length = (4 * 4
	  + nettle_mpz_sizeinbase_256_u(pub->n)
	  + nettle_mpz_sizeinbase_256_u(pub->e));

  if (!pgp_put_header(buffer, PGP_TAG_PUBLIC_KEY, length))
    return 0;

  start = buffer->size;
  
  if (! (pgp_put_header(buffer, PGP_TAG_PUBLIC_KEY,
			/* Assume that we need two octets */
			PGP_LENGTH_TWO_OCTETS)
	 && pgp_put_uint32(buffer, 4)        /* Version */  
	 && pgp_put_uint32(buffer, timestamp)/* Time stamp */
	 && pgp_put_uint32(buffer, PGP_RSA)  /* Algorithm */
	 && pgp_put_mpi(buffer, pub->n)
	 && pgp_put_mpi(buffer, pub->e)) )
    return 0;

  assert(buffer->size == start + length);

  return 1;
}

int
pgp_put_rsa_sha1_signature(struct nettle_buffer *buffer,
			   const struct rsa_private_key *key,
			   const uint8_t *keyid,
			   unsigned type,
			   struct sha1_ctx *hash)
{
  unsigned signature_start = buffer->size;
  unsigned hash_end;
  unsigned sub_packet_start;
  uint8_t trailer[6];
  uint8_t digest16[2];
  mpz_t s;
  
  /* Signature packet. The packet could reasonably be both smaller and
   * larger than 192, so for simplicity we use the 4 octet header
   * form. */

  if (! (pgp_put_header(buffer, PGP_TAG_SIGNATURE, PGP_LENGTH_FOUR_OCTETS)
	 && NETTLE_BUFFER_PUTC(buffer, 4)  /* Version */
	 && NETTLE_BUFFER_PUTC(buffer, type)
	 /* Could also be PGP_RSA_SIGN */
	 && NETTLE_BUFFER_PUTC(buffer, PGP_RSA)
	 && NETTLE_BUFFER_PUTC(buffer, PGP_SHA1)
	 && pgp_put_uint16(buffer, 0)))  /* Hashed subpacket length */
    return 0;

  hash_end = buffer->size;

  sha1_update(hash,
	      hash_end - signature_start,
	      buffer->contents + signature_start);

  trailer[0] = 4; trailer[1] = 0xff;
  WRITE_UINT32(trailer + 2, buffer->size - signature_start);

  sha1_update(hash, sizeof(trailer), trailer);

  {
    struct sha1_ctx hcopy = *hash;
    uint8_t *p = nettle_buffer_space(buffer, 2);
    if (!p)
      return 0;
    
    sha1_digest(&hcopy, 2, p);
  }

  /* One "sub-packet" field with the issuer keyid */
  sub_packet_start = pgp_sub_packet_start(buffer);
  if (!sub_packet_start)
    return 0;

  if (pgp_put_sub_packet(buffer, PGP_SUBPACKET_ISSUER_KEY_ID, 8, keyid))
    {
      pgp_sub_packet_end(buffer, sub_packet_start);
      return 0;
    }
    
  mpz_init(s);
  rsa_sha1_sign(key, hash, s);

  if (!pgp_put_mpi(buffer, s))
    {
      mpz_clear(s);
      return 0;
    }

  mpz_clear(s);
  pgp_put_header_length(buffer, signature_start, 4);

  return 1;
}
#endif /* WITH_PUBLIC_KEY */

#define CRC24_INIT 0x0b704ceL
#define CRC24_POLY 0x1864cfbL

uint32_t
pgp_crc24(unsigned length, const uint8_t *data)
{
  uint32_t crc = CRC24_INIT;

  unsigned i;
  for (i = 0; i<length; i++)
    {
      unsigned j;
      crc ^= ((unsigned) (data[i]) << 16);
      for (j = 0; j<8; j++)
	{
	  crc <<= 1;
	  if (crc & 0x1000000)
	    crc ^= CRC24_POLY;
	}
    }
  assert(crc < 0x1000000);
  return crc;
}


#define WRITE(buffer, s) (nettle_buffer_write(buffer, strlen((s)), (s)))

/* 15 base 64 groups data per line */
#define BINARY_PER_LINE 45
#define TEXT_PER_LINE BASE64_ENCODE_LENGTH(BINARY_PER_LINE)

int
pgp_armor(struct nettle_buffer *buffer,
	  const char *tag,
	  unsigned length,
	  const uint8_t *data)
{
  struct base64_encode_ctx ctx;
  
  unsigned crc = pgp_crc24(length, data);

  base64_encode_init(&ctx);
  
  if (! (WRITE(buffer, "BEGIN PGP ")
	 && WRITE(buffer, tag)
	 && WRITE(buffer, "\nComment: Nettle\n\n")))
    return 0;

  for (;
       length >= BINARY_PER_LINE;
       length -= BINARY_PER_LINE, data += BINARY_PER_LINE)
    {
      unsigned done;
      uint8_t *p
	= nettle_buffer_space(buffer, TEXT_PER_LINE);
      
      if (!p)
	return 0;

      done = base64_encode_update(&ctx, p, BINARY_PER_LINE, data);
      assert(done <= TEXT_PER_LINE);

      /* FIXME: Create some official way to do this */
      buffer->size -= (TEXT_PER_LINE - done);
      
      if (!NETTLE_BUFFER_PUTC(buffer, '\n'))
	return 0;
    }

  if (length)
    {
      unsigned text_size = BASE64_ENCODE_LENGTH(length)
	+ BASE64_ENCODE_FINAL_LENGTH;
      unsigned done;
      
      uint8_t *p
	= nettle_buffer_space(buffer, text_size);
      if (!p)
	return 0;

      done = base64_encode_update(&ctx, p, length, data);
      done += base64_encode_final(&ctx, p + done);

      /* FIXME: Create some official way to do this */
      buffer->size -= (text_size - done);
      
      if (!NETTLE_BUFFER_PUTC(buffer, '\n'))
	return 0;
    }
  /* Checksum */
  if (!NETTLE_BUFFER_PUTC(buffer, '='))
    return 0;

  {
    uint8_t *p = nettle_buffer_space(buffer, 4);
    if (!p)
      return 0;
    base64_encode_group(p, crc);
  }
  
  return (WRITE(buffer, "\nBEGIN PGP ")
	  && WRITE(buffer, tag)
	  && NETTLE_BUFFER_PUTC(buffer, '\n'));
}