/*
 * Copyright 1986, 1987, 1988 by the Massachusetts Institute
 * of Technology.
 * For copying and distribution information, please see the file
 * <Copyright.MIT>.
 *
 * This routine dissects a a Kerberos 'safe msg', checking its
 * integrity, and returning a pointer to the application data
 * contained and its length.
 *
 * Returns 0 (RD_AP_OK) for success or an error code (RD_AP_...)
 *
 * Steve Miller    Project Athena  MIT/DEC
 *
 *	from: rd_safe.c,v 4.12 89/01/23 15:16:16 steiner Exp $
 *	$Id: rd_safe.c,v 1.3 1995/07/18 16:39:34 mark Exp $
 */

#if 0
#ifndef lint
static char rcsid[] =
"$Id: rd_safe.c,v 1.3 1995/07/18 16:39:34 mark Exp $";
#endif /* lint */
#endif

/* system include files */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/time.h>

/* application include files */
#include <des.h>
#include <krb.h>
#include <prot.h>
#include "lsb_addr_comp.h"

extern char *errmsg();
extern int errno;
extern int krb_debug;

/* static storage */

static C_Block calc_cksum[2];
static C_Block big_cksum[2];
static int swap_bytes;
static struct timeval local_time;
static u_long delta_t;

/*
 * krb_rd_safe() checks the integrity of an AUTH_MSG_SAFE message.
 * Given the message received, "in", the length of that message,
 * "in_length", the "key" to compute the checksum with, and the
 * network addresses of the "sender" and "receiver" of the message,
 * krb_rd_safe() returns RD_AP_OK if message is okay, otherwise
 * some error code.
 *
 * The message data retrieved from "in" is returned in the structure
 * "m_data".  The pointer to the application data (m_data->app_data)
 * refers back to the appropriate place in "in".
 *
 * See the file "mk_safe.c" for the format of the AUTH_MSG_SAFE
 * message.  The structure containing the extracted message
 * information, MSG_DAT, is defined in "krb.h".
 */

long krb_rd_safe(in,in_length,key,sender,receiver,m_data)
    u_char *in;                 /* pointer to the msg received */
    u_long in_length;           /* length of "in" msg */
    C_Block *key;               /* encryption key for seed and ivec */
    struct sockaddr_in *sender; /* sender's address */
    struct sockaddr_in *receiver; /* receiver's address -- me */
    MSG_DAT *m_data;		/* where to put message information */
{
    register u_char     *p,*q;
    static      u_long  src_addr; /* Can't send structs since no
                                   * guarantees on size */
    /* Be very conservative */
    if (sizeof(u_long) != sizeof(struct in_addr)) {
        fprintf(stderr,"\n\
krb_rd_safe protocol err sizeof(u_long) != sizeof(struct in_addr)");
        exit(-1);
    }

    if (gettimeofday(&local_time,(struct timezone *)0))
        return  -1;

    p = in;                     /* beginning of message */
    swap_bytes = 0;

    if (*p++ != KRB_PROT_VERSION)       return RD_AP_VERSION;
    if (((*p) & ~1) != AUTH_MSG_SAFE) return RD_AP_MSG_TYPE;
    if ((*p++ & 1) != HOST_BYTE_ORDER) swap_bytes++;

    q = p;                      /* mark start of cksum stuff */

    /* safely get length */
    bcopy((char *)p,(char *)&(m_data->app_length),
          sizeof(m_data->app_length));
    if (swap_bytes) swap_u_long(m_data->app_length);
    p += sizeof(m_data->app_length); /* skip over */

    if (m_data->app_length + sizeof(in_length)
        + sizeof(m_data->time_sec) + sizeof(m_data->time_5ms)
        + sizeof(big_cksum) + sizeof(src_addr)
        + VERSION_SZ + MSG_TYPE_SZ > in_length)
        return(RD_AP_MODIFIED);

    m_data->app_data = p;       /* we're now at the application data */

    /* skip app data */
    p += m_data->app_length;

    /* safely get time_5ms */
    bcopy((char *)p, (char *)&(m_data->time_5ms),
          sizeof(m_data->time_5ms));

    /* don't need to swap-- one byte for now */
    p += sizeof(m_data->time_5ms);

    /* safely get src address */
    bcopy((char *)p,(char *)&src_addr,sizeof(src_addr));

    /* don't swap, net order always */
    p += sizeof(src_addr);

    if (src_addr != (u_long) sender->sin_addr.s_addr)
        return RD_AP_MODIFIED;

    /* safely get time_sec */
    bcopy((char *)p, (char *)&(m_data->time_sec),
          sizeof(m_data->time_sec));
    if (swap_bytes)
        swap_u_long(m_data->time_sec);
    p += sizeof(m_data->time_sec);

    /* check direction bit is the sign bit */
    /* For compatibility with broken old code, compares are done in VAX
       byte order (LSBFIRST) */
    if (lsb_net_ulong_less(sender->sin_addr.s_addr,
			   receiver->sin_addr.s_addr)==-1)
	/* src < recv */
	m_data->time_sec =  - m_data->time_sec;
    else if (lsb_net_ulong_less(sender->sin_addr.s_addr,
				receiver->sin_addr.s_addr)==0)
	if (lsb_net_ushort_less(sender->sin_port,receiver->sin_port)==-1)
	    /* src < recv */
	    m_data->time_sec =  - m_data->time_sec;

    /*
     * All that for one tiny bit!  Heaven help those that talk to
     * themselves.
     */

    /* check the time integrity of the msg */
    delta_t = abs((int)((long) local_time.tv_sec - m_data->time_sec));
    if (delta_t > CLOCK_SKEW) return RD_AP_TIME;

    /*
     * caller must check timestamps for proper order and replays, since
     * server might have multiple clients each with its own timestamps
     * and we don't assume tightly synchronized clocks.
     */

    bcopy((char *)p,(char *)big_cksum,sizeof(big_cksum));
    if (swap_bytes) swap_u_16(big_cksum);

#ifdef NOENCRYPTION
    bzero(calc_cksum, sizeof(calc_cksum));
#else
    quad_cksum((C_Block *)q,calc_cksum,p-q,2,key);
#endif

    if (krb_debug)
        printf("\ncalc_cksum = %lu, received cksum = %lu",
               (long) calc_cksum[0], (long) big_cksum[0]);
    if (bcmp((char *)big_cksum,(char *)calc_cksum,sizeof(big_cksum)))
        return(RD_AP_MODIFIED);

    return(RD_AP_OK);           /* OK == 0 */
}
