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i bet a lot of people didn't know what ssh 1.2.16 had a nice license.
well, except for the patent issues.  someone in sweden (forget their
name at the moment) cleaned out most of the patented code, and now
this code removes rsa code.  when this is done, it will link against
libssl, but the work isn't completely done yet.  then we need to bring
this up to modern days, featurewise.

/*

authfile.c

Author: Tatu Ylonen <ylo@cs.hut.fi>

Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
                   All rights reserved

Created: Mon Mar 27 03:52:05 1995 ylo

This file contains functions for reading and writing identity files, and
for reading the passphrase from the user.

*/

#include "includes.h"
RCSID("$Id: authfile.c,v 1.1 1999/09/26 20:53:33 deraadt Exp $");

#include <gmp.h>
#include "xmalloc.h"
#include "idea.h"
#include "buffer.h"
#include "bufaux.h"
#include "cipher.h"
#include "ssh.h"

/* Version identification string for identity files. */
#define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n"

/* Saves the authentication (private) key in a file, encrypting it with
   passphrase.  The identification of the file (lowest 64 bits of n)
   will precede the key to provide identification of the key without
   needing a passphrase. */

int save_private_key(const char *filename, const char *passphrase,
		     RSAPrivateKey *key, const char *comment, 
		     RandomState *state)
{
  Buffer buffer, encrypted;
  char buf[100], *cp;
  int f, i;
  CipherContext cipher;
  int cipher_type;

  /* If the passphrase is empty, use SSH_CIPHER_NONE to ease converting to
     another cipher; otherwise use SSH_AUTHFILE_CIPHER. */
  if (strcmp(passphrase, "") == 0)
    cipher_type = SSH_CIPHER_NONE;
  else
    cipher_type = SSH_AUTHFILE_CIPHER;

  /* This buffer is used to built the secret part of the private key. */
  buffer_init(&buffer);
  
  /* Put checkbytes for checking passphrase validity. */
  buf[0] = random_get_byte(state);
  buf[1] = random_get_byte(state);
  buf[2] = buf[0];
  buf[3] = buf[1];
  buffer_append(&buffer, buf, 4);

  /* Store the private key (n and e will not be stored because they will
     be stored in plain text, and storing them also in encrypted format
     would just give known plaintext). */
  buffer_put_mp_int(&buffer, &key->d);
  buffer_put_mp_int(&buffer, &key->u);
  buffer_put_mp_int(&buffer, &key->p);
  buffer_put_mp_int(&buffer, &key->q);

  /* Pad the part to be encrypted until its size is a multiple of 8. */
  while (buffer_len(&buffer) % 8 != 0)
    buffer_put_char(&buffer, 0);

  /* This buffer will be used to contain the data in the file. */
  buffer_init(&encrypted);

  /* First store keyfile id string. */
  cp = AUTHFILE_ID_STRING;
  for (i = 0; cp[i]; i++)
    buffer_put_char(&encrypted, cp[i]);
  buffer_put_char(&encrypted, 0);

  /* Store cipher type. */
  buffer_put_char(&encrypted, cipher_type);
  buffer_put_int(&encrypted, 0);  /* For future extension */

  /* Store public key.  This will be in plain text. */
  buffer_put_int(&encrypted, key->bits);
  buffer_put_mp_int(&encrypted, &key->n);
  buffer_put_mp_int(&encrypted, &key->e);
  buffer_put_string(&encrypted, comment, strlen(comment));

  /* Allocate space for the private part of the key in the buffer. */
  buffer_append_space(&encrypted, &cp, buffer_len(&buffer));

  cipher_set_key_string(&cipher, cipher_type, passphrase, 1);
  cipher_encrypt(&cipher, (unsigned char *)cp, 
		 (unsigned char *)buffer_ptr(&buffer),
		 buffer_len(&buffer));
  memset(&cipher, 0, sizeof(cipher));

  /* Destroy temporary data. */
  memset(buf, 0, sizeof(buf));
  buffer_free(&buffer);

  /* Write to a file. */
  f = open(filename, O_WRONLY|O_CREAT|O_TRUNC, 0600);
  if (f < 0)
    return 0;

  if (write(f, buffer_ptr(&encrypted), buffer_len(&encrypted)) != 
      buffer_len(&encrypted))
    {
      debug("Write to key file %.200s failed: %.100s", filename,
	    strerror(errno));
      buffer_free(&encrypted);
      close(f);
      remove(filename);
      return 0;
    }
  close(f);
  buffer_free(&encrypted);
  return 1;
}

/* Loads the public part of the key file.  Returns 0 if an error
   was encountered (the file does not exist or is not readable), and
   non-zero otherwise. */

int load_public_key(const char *filename, RSAPublicKey *pub, 
		    char **comment_return)
{
  int f, i;
  unsigned long len;
  Buffer buffer;
  char *cp;

  /* Read data from the file into the buffer. */
  f = open(filename, O_RDONLY);
  if (f < 0)
    return 0;

  len = lseek(f, (off_t)0L, 2);
  lseek(f, (off_t)0L, 0);
  
  buffer_init(&buffer);
  buffer_append_space(&buffer, &cp, len);

  if (read(f, cp, len) != len)
    {
      debug("Read from key file %.200s failed: %.100s", filename, 
	    strerror(errno));
      buffer_free(&buffer);
      close(f);
      return 0;
    }
  close(f);

  /* Check that it is at least big enought to contain the ID string. */
  if (len < strlen(AUTHFILE_ID_STRING) + 1)
    {
      debug("Bad key file %.200s.", filename);
      buffer_free(&buffer);
      return 0;
    }

  /* Make sure it begins with the id string.  Consume the id string from
     the buffer. */
  for (i = 0; i < (unsigned int)strlen(AUTHFILE_ID_STRING) + 1; i++)
    if (buffer_get_char(&buffer) != (unsigned char)AUTHFILE_ID_STRING[i])
      {
	debug("Bad key file %.200s.", filename);
	buffer_free(&buffer);
	return 0;
      }

  /* Skip cipher type and reserved data. */
  (void)buffer_get_char(&buffer); /* cipher type */
  (void)buffer_get_int(&buffer); /* reserved */

  /* Read the public key from the buffer. */
  pub->bits = buffer_get_int(&buffer);
  mpz_init(&pub->n);
  buffer_get_mp_int(&buffer, &pub->n);
  mpz_init(&pub->e);
  buffer_get_mp_int(&buffer, &pub->e);
  if (comment_return)
    *comment_return = buffer_get_string(&buffer, NULL);
  /* The encrypted private part is not parsed by this function. */

  buffer_free(&buffer);
  
  return 1;
}

/* Loads the private key from the file.  Returns 0 if an error is encountered
   (file does not exist or is not readable, or passphrase is bad).
   This initializes the private key. */

int load_private_key(const char *filename, const char *passphrase,
		     RSAPrivateKey *prv, char **comment_return)
{
  int f, i, check1, check2, cipher_type;
  unsigned long len;
  Buffer buffer, decrypted;
  char *cp;
  CipherContext cipher;

  /* Read the file into the buffer. */
  f = open(filename, O_RDONLY);
  if (f < 0)
    return 0;

  len = lseek(f, (off_t)0L, 2);
  lseek(f, (off_t)0L, 0);
  
  buffer_init(&buffer);
  buffer_append_space(&buffer, &cp, len);

  if (read(f, cp, len) != len)
    {
      debug("Read from key file %.200s failed: %.100s", filename,
	    strerror(errno));
      buffer_free(&buffer);
      close(f);
      return 0;
    }
  close(f);

  /* Check that it is at least big enought to contain the ID string. */
  if (len < strlen(AUTHFILE_ID_STRING) + 1)
    {
      debug("Bad key file %.200s.", filename);
      buffer_free(&buffer);
      return 0;
    }

  /* Make sure it begins with the id string.  Consume the id string from
     the buffer. */
  for (i = 0; i < (unsigned int)strlen(AUTHFILE_ID_STRING) + 1; i++)
    if (buffer_get_char(&buffer) != (unsigned char)AUTHFILE_ID_STRING[i])
      {
	debug("Bad key file %.200s.", filename);
	buffer_free(&buffer);
	return 0;
      }

  /* Read cipher type. */
  cipher_type = buffer_get_char(&buffer);
  (void)buffer_get_int(&buffer);  /* Reserved data. */

  /* Read the public key from the buffer. */
  prv->bits = buffer_get_int(&buffer);
  mpz_init(&prv->n);
  buffer_get_mp_int(&buffer, &prv->n);
  mpz_init(&prv->e);
  buffer_get_mp_int(&buffer, &prv->e);
  if (comment_return)
    *comment_return = buffer_get_string(&buffer, NULL);
  else
    xfree(buffer_get_string(&buffer, NULL));

  /* Check that it is a supported cipher. */
  if ((cipher_mask() & (1 << cipher_type)) == 0)
    {
      debug("Unsupported cipher %.100s used in key file %.200s.",
	    cipher_name(cipher_type), filename);
      buffer_free(&buffer);
      goto fail;
    }

  /* Initialize space for decrypted data. */
  buffer_init(&decrypted);
  buffer_append_space(&decrypted, &cp, buffer_len(&buffer));
      
  /* Rest of the buffer is encrypted.  Decrypt it using the passphrase. */
  cipher_set_key_string(&cipher, cipher_type, passphrase, 0);
  cipher_decrypt(&cipher, (unsigned char *)cp,
		 (unsigned char *)buffer_ptr(&buffer),
		 buffer_len(&buffer));

  buffer_free(&buffer);

  check1 = buffer_get_char(&decrypted);
  check2 = buffer_get_char(&decrypted);
  if (check1 != buffer_get_char(&decrypted) ||
      check2 != buffer_get_char(&decrypted))
    {
      if (strcmp(passphrase, "") != 0)
	debug("Bad passphrase supplied for key file %.200s.", filename);
      /* Bad passphrase. */
      buffer_free(&decrypted);
    fail:
      mpz_clear(&prv->n);
      mpz_clear(&prv->e);
      if (comment_return)
	xfree(*comment_return);
      return 0;
    }

  /* Read the rest of the private key. */
  mpz_init(&prv->d);
  buffer_get_mp_int(&decrypted, &prv->d);
  mpz_init(&prv->u);
  buffer_get_mp_int(&decrypted, &prv->u);
  mpz_init(&prv->p);
  buffer_get_mp_int(&decrypted, &prv->p);
  mpz_init(&prv->q);
  buffer_get_mp_int(&decrypted, &prv->q);
  
  buffer_free(&decrypted);

  return 1;
}