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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.

/*

readpass.c

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

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

Created: Mon Jul 10 22:08:59 1995 ylo

Functions for reading passphrases and passwords.

*/

#include "includes.h"
RCSID("$Id: readpass.c,v 1.1 1999/09/26 20:53:37 deraadt Exp $");

#include "xmalloc.h"
#include "ssh.h"

/* Saved old terminal mode for read_passphrase. */
#ifdef USING_TERMIOS
static struct termios saved_tio;
#endif
#ifdef USING_SGTTY
static struct sgttyb saved_tio;
#endif

/* Old interrupt signal handler for read_passphrase. */
static RETSIGTYPE (*old_handler)(int sig) = NULL;

/* Interrupt signal handler for read_passphrase. */

RETSIGTYPE intr_handler(int sig)
{
  /* Restore terminal modes. */
#ifdef USING_TERMIOS
  tcsetattr(fileno(stdin), TCSANOW, &saved_tio);
#endif
#ifdef USING_SGTTY
  ioctl(fileno(stdin), TIOCSETP, &saved_tio);
#endif
  /* Restore the old signal handler. */
  signal(sig, old_handler);
  /* Resend the signal, with the old handler. */
  kill(getpid(), sig);
}

/* Reads a passphrase from /dev/tty with echo turned off.  Returns the 
   passphrase (allocated with xmalloc).  Exits if EOF is encountered. 
   The passphrase if read from stdin if from_stdin is true (as is the
   case with ssh-keygen).  */

char *read_passphrase(const char *prompt, int from_stdin)
{
  char buf[1024], *cp;
#ifdef USING_TERMIOS
  struct termios tio;
#endif
#ifdef USING_SGTTY
  struct sgttyb tio;
#endif
  FILE *f;
  
  if (from_stdin)
    f = stdin;
  else
    {
      /* Read the passphrase from /dev/tty to make it possible to ask it even 
	 when stdin has been redirected. */
      f = fopen("/dev/tty", "r");
      if (!f)
	{
	  if (getenv("DISPLAY"))
	    {
	      char command[512];
	      fprintf(stderr,
		      "Executing ssh-askpass to query the password...\n");
	      fflush(stdout);
	      fflush(stderr);
	      sprintf(command, "ssh-askpass '%.400s'", prompt);
	      f = popen(command, "r");
	      if (!fgets(buf, sizeof(buf), f))
		{
		  pclose(f);
		  fprintf(stderr, "No passphrase supplied.  Exiting.\n");
		  exit(1);
		}
	      pclose(f);
	      if (strchr(buf, '\n'))
		*strchr(buf, '\n') = 0;
	      return xstrdup(buf);
	    }

	  /* No controlling terminal and no DISPLAY.  Nowhere to read. */
	  fprintf(stderr, "You have no controlling tty and no DISPLAY.  Cannot read passphrase.\n");
	  exit(1);
	}
    }

  /* Display the prompt (on stderr because stdout might be redirected). */
  fflush(stdout);
  fprintf(stderr, "%s", prompt);
  fflush(stderr);

  /* Get terminal modes. */
#ifdef USING_TERMIOS
  tcgetattr(fileno(f), &tio);
#endif
#ifdef USING_SGTTY
  ioctl(fileno(f), TIOCGETP, &tio);
#endif
  saved_tio = tio;
  /* Save signal handler and set the new handler. */
  old_handler = signal(SIGINT, intr_handler);

  /* Set new terminal modes disabling all echo. */
#ifdef USING_TERMIOS
  tio.c_lflag &= ~(ECHO | ECHOE | ECHOK | ECHONL);
  tcsetattr(fileno(f), TCSANOW, &tio);
#endif
#ifdef USING_SGTTY
  tio.sg_flags &= ~(ECHO);
  ioctl(fileno(f), TIOCSETP, &tio);
#endif

  /* Read the passphrase from the terminal. */
  if (fgets(buf, sizeof(buf), f) == NULL)
    {
      /* Got EOF.  Just exit. */
      /* Restore terminal modes. */
#ifdef USING_TERMIOS
      tcsetattr(fileno(f), TCSANOW, &saved_tio);
#endif
#ifdef USING_SGTTY
      ioctl(fileno(f), TIOCSETP, &saved_tio);
#endif
      /* Restore the signal handler. */
      signal(SIGINT, old_handler);
      /* Print a newline (the prompt probably didn\'t have one). */
      fprintf(stderr, "\n");
      /* Close the file. */
      if (f != stdin)
	fclose(f);
      exit(1);
    }
  /* Restore terminal modes. */
#ifdef USING_TERMIOS
  tcsetattr(fileno(f), TCSANOW, &saved_tio);
#endif
#ifdef USING_SGTTY
  ioctl(fileno(f), TIOCSETP, &saved_tio);
#endif
  /* Restore the signal handler. */
  (void)signal(SIGINT, old_handler);
  /* Remove newline from the passphrase. */
  if (strchr(buf, '\n'))
    *strchr(buf, '\n') = 0;
  /* Allocate a copy of the passphrase. */
  cp = xstrdup(buf);
  /* Clear the buffer so we don\'t leave copies of the passphrase laying
     around. */
  memset(buf, 0, sizeof(buf));
  /* Print a newline since the prompt probably didn\'t have one. */
  fprintf(stderr, "\n");
  /* Close the file. */
  if (f != stdin)
    fclose(f);
  return cp;
}