lib/libtelnet/enc_des.c

   1 /*-
   2  * Copyright (c) 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * $FreeBSD: src/crypto/telnet/libtelnet/enc_des.c,v 1.3.2.1 2002/04/13 10:59:07 markm Exp $
  34  */
  35
  36 #include <sys/cdefs.h>
  37
  38 #ifdef __FBSDID
  39 __FBSDID("$FreeBSD: src/crypto/telnet/libtelnet/enc_des.c,v 1.3.2.1 2002/04/13 10:59:07 markm Exp $");
  40 #endif
  41
  42 #ifndef __unused
  43 #define __unused        __attribute__((__unused__))
  44 #endif
  45
  46 #ifndef lint
  47 static const char sccsid[] = "@(#)enc_des.c     8.3 (Berkeley) 5/30/95";
  48 #endif /* not lint */
  49
  50 #ifdef  ENCRYPTION
  51 # ifdef AUTHENTICATION
  52 #include <arpa/telnet.h>
  53 #include <des.h>
  54 #include <stdio.h>
  55 #include <stdlib.h>
  56 #include <string.h>
  57
  58 #include "encrypt.h"
  59 #include "key-proto.h"
  60 #include "misc-proto.h"
  61
  62 extern int encrypt_debug_mode;
  63
  64 #define CFB     0
  65 #define OFB     1
  66
  67 #define NO_SEND_IV      1
  68 #define NO_RECV_IV      2
  69 #define NO_KEYID        4
  70 #define IN_PROGRESS     (NO_SEND_IV|NO_RECV_IV|NO_KEYID)
  71 #define SUCCESS         0
  72 #define FAILED          -1
  73
  74
  75 struct fb {
  76         Block krbdes_key;
  77         Schedule krbdes_sched;
  78         Block temp_feed;
  79         unsigned char fb_feed[64];
  80         int need_start;
  81         int state[2];
  82         int keyid[2];
  83         int once;
  84         struct stinfo {
  85                 Block           str_output;
  86                 Block           str_feed;
  87                 Block           str_iv;
  88                 Block           str_ikey;
  89                 Schedule        str_sched;
  90                 int             str_index;
  91                 int             str_flagshift;
  92         } streams[2];
  93 };
  94
  95 static struct fb fb[2];
  96
  97 struct keyidlist {
  98         const char *keyid;
  99         int     keyidlen;
 100         char    *key;
 101         int     keylen;
 102         int     flags;
 103 } keyidlist [] = {
 104         { "\0", 1, 0, 0, 0 },           /* default key of zero */
 105         { 0, 0, 0, 0, 0 }
 106 };
 107
 108 #define KEYFLAG_MASK    03
 109
 110 #define KEYFLAG_NOINIT  00
 111 #define KEYFLAG_INIT    01
 112 #define KEYFLAG_OK      02
 113 #define KEYFLAG_BAD     03
 114
 115 #define KEYFLAG_SHIFT   2
 116
 117 #define SHIFT_VAL(a,b)  (KEYFLAG_SHIFT*((a)+((b)*2)))
 118
 119 #define FB64_IV         1
 120 #define FB64_IV_OK      2
 121 #define FB64_IV_BAD     3
 122
 123
 124 void fb64_stream_iv(Block, struct stinfo *);
 125 void fb64_init(struct fb *);
 126 static int fb64_start(struct fb *, int, int);
 127 int fb64_is(unsigned char *, int, struct fb *);
 128 int fb64_reply(unsigned char *, int, struct fb *);
 129 static void fb64_session(Session_Key *, int, struct fb *);
 130 void fb64_stream_key(Block, struct stinfo *);
 131 int fb64_keyid(int, unsigned char *, int *, struct fb *);
 132
 133 void
 134 cfb64_init(int server __unused)
 135 {
 136         fb64_init(&fb[CFB]);
 137         fb[CFB].fb_feed[4] = ENCTYPE_DES_CFB64;
 138         fb[CFB].streams[0].str_flagshift = SHIFT_VAL(0, CFB);
 139         fb[CFB].streams[1].str_flagshift = SHIFT_VAL(1, CFB);
 140 }
 141
 142 void
 143 ofb64_init(int server __unused)
 144 {
 145         fb64_init(&fb[OFB]);
 146         fb[OFB].fb_feed[4] = ENCTYPE_DES_OFB64;
 147         fb[CFB].streams[0].str_flagshift = SHIFT_VAL(0, OFB);
 148         fb[CFB].streams[1].str_flagshift = SHIFT_VAL(1, OFB);
 149 }
 150
 151 void
 152 fb64_init(struct fb *fbp)
 153 {
 154         memset((void *)fbp, 0, sizeof(*fbp));
 155         fbp->state[0] = fbp->state[1] = FAILED;
 156         fbp->fb_feed[0] = IAC;
 157         fbp->fb_feed[1] = SB;
 158         fbp->fb_feed[2] = TELOPT_ENCRYPT;
 159         fbp->fb_feed[3] = ENCRYPT_IS;
 160 }
 161
 162 /*
 163  * Returns:
 164  *      -1: some error.  Negotiation is done, encryption not ready.
 165  *       0: Successful, initial negotiation all done.
 166  *       1: successful, negotiation not done yet.
 167  *       2: Not yet.  Other things (like getting the key from
 168  *          Kerberos) have to happen before we can continue.
 169  */
 170 int
 171 cfb64_start(int dir, int server)
 172 {
 173         return(fb64_start(&fb[CFB], dir, server));
 174 }
 175
 176 int
 177 ofb64_start(int dir, int server)
 178 {
 179         return(fb64_start(&fb[OFB], dir, server));
 180 }
 181
 182 static int
 183 fb64_start(struct fb *fbp, int dir, int server __unused)
 184 {
 185         size_t x;
 186         unsigned char *p;
 187         int state;
 188
 189         switch (dir) {
 190         case DIR_DECRYPT:
 191                 /*
 192                  * This is simply a request to have the other side
 193                  * start output (our input).  He will negotiate an
 194                  * IV so we need not look for it.
 195                  */
 196                 state = fbp->state[dir-1];
 197                 if (state == FAILED)
 198                         state = IN_PROGRESS;
 199                 break;
 200
 201         case DIR_ENCRYPT:
 202                 state = fbp->state[dir-1];
 203                 if (state == FAILED)
 204                         state = IN_PROGRESS;
 205                 else if ((state & NO_SEND_IV) == 0)
 206                         break;
 207
 208                 if (!VALIDKEY(fbp->krbdes_key)) {
 209                         fbp->need_start = 1;
 210                         break;
 211                 }
 212                 state &= ~NO_SEND_IV;
 213                 state |= NO_RECV_IV;
 214                 if (encrypt_debug_mode)
 215                         printf("Creating new feed\r\n");
 216                 /*
 217                  * Create a random feed and send it over.
 218                  */
 219                 des_new_random_key(fbp->temp_feed);
 220                 des_ecb_encrypt((Block *)fbp->temp_feed, (Block *)fbp->temp_feed,
 221                                 fbp->krbdes_sched, 1);
 222                 p = fbp->fb_feed + 3;
 223                 *p++ = ENCRYPT_IS;
 224                 p++;
 225                 *p++ = FB64_IV;
 226                 for (x = 0; x < sizeof(Block); ++x) {
 227                         if ((*p++ = fbp->temp_feed[x]) == IAC)
 228                                 *p++ = IAC;
 229                 }
 230                 *p++ = IAC;
 231                 *p++ = SE;
 232                 printsub('>', &fbp->fb_feed[2], p - &fbp->fb_feed[2]);
 233                 net_write(fbp->fb_feed, p - fbp->fb_feed);
 234                 break;
 235         default:
 236                 return(FAILED);
 237         }
 238         return(fbp->state[dir-1] = state);
 239 }
 240
 241 /*
 242  * Returns:
 243  *      -1: some error.  Negotiation is done, encryption not ready.
 244  *       0: Successful, initial negotiation all done.
 245  *       1: successful, negotiation not done yet.
 246  */
 247 int
 248 cfb64_is(unsigned char *data, int cnt)
 249 {
 250         return(fb64_is(data, cnt, &fb[CFB]));
 251 }
 252
 253 int
 254 ofb64_is(unsigned char *data, int cnt)
 255 {
 256         return(fb64_is(data, cnt, &fb[OFB]));
 257 }
 258
 259 int
 260 fb64_is(unsigned char *data, int cnt, struct fb *fbp)
 261 {
 262         unsigned char *p;
 263         int state = fbp->state[DIR_DECRYPT-1];
 264
 265         if (cnt-- < 1)
 266                 goto failure;
 267
 268         switch (*data++) {
 269         case FB64_IV:
 270                 if (cnt != sizeof(Block)) {
 271                         if (encrypt_debug_mode)
 272                                 printf("CFB64: initial vector failed on size\r\n");
 273                         state = FAILED;
 274                         goto failure;
 275                 }
 276
 277                 if (encrypt_debug_mode)
 278                         printf("CFB64: initial vector received\r\n");
 279
 280                 if (encrypt_debug_mode)
 281                         printf("Initializing Decrypt stream\r\n");
 282
 283                 fb64_stream_iv((void *)data, &fbp->streams[DIR_DECRYPT-1]);
 284
 285                 p = fbp->fb_feed + 3;
 286                 *p++ = ENCRYPT_REPLY;
 287                 p++;
 288                 *p++ = FB64_IV_OK;
 289                 *p++ = IAC;
 290                 *p++ = SE;
 291                 printsub('>', &fbp->fb_feed[2], p - &fbp->fb_feed[2]);
 292                 net_write(fbp->fb_feed, p - fbp->fb_feed);
 293
 294                 state = fbp->state[DIR_DECRYPT-1] = IN_PROGRESS;
 295                 break;
 296
 297         default:
 298                 if (encrypt_debug_mode) {
 299                         printf("Unknown option type: %d\r\n", *(data-1));
 300                         printd(data, cnt);
 301                         printf("\r\n");
 302                 }
 303                 /* FALL THROUGH */
 304         failure:
 305                 /*
 306                  * We failed.  Send an FB64_IV_BAD option
 307                  * to the other side so it will know that
 308                  * things failed.
 309                  */
 310                 p = fbp->fb_feed + 3;
 311                 *p++ = ENCRYPT_REPLY;
 312                 p++;
 313                 *p++ = FB64_IV_BAD;
 314                 *p++ = IAC;
 315                 *p++ = SE;
 316                 printsub('>', &fbp->fb_feed[2], p - &fbp->fb_feed[2]);
 317                 net_write(fbp->fb_feed, p - fbp->fb_feed);
 318
 319                 break;
 320         }
 321         return(fbp->state[DIR_DECRYPT-1] = state);
 322 }
 323
 324 /*
 325  * Returns:
 326  *      -1: some error.  Negotiation is done, encryption not ready.
 327  *       0: Successful, initial negotiation all done.
 328  *       1: successful, negotiation not done yet.
 329  */
 330 int
 331 cfb64_reply(unsigned char *data, int cnt)
 332 {
 333         return(fb64_reply(data, cnt, &fb[CFB]));
 334 }
 335
 336 int
 337 ofb64_reply(unsigned char *data, int cnt)
 338 {
 339         return(fb64_reply(data, cnt, &fb[OFB]));
 340 }
 341
 342 int
 343 fb64_reply(unsigned char *data, int cnt, struct fb *fbp)
 344 {
 345         int state = fbp->state[DIR_ENCRYPT-1];
 346
 347         if (cnt-- < 1)
 348                 goto failure;
 349
 350         switch (*data++) {
 351         case FB64_IV_OK:
 352                 fb64_stream_iv(fbp->temp_feed, &fbp->streams[DIR_ENCRYPT-1]);
 353                 if (state == FAILED)
 354                         state = IN_PROGRESS;
 355                 state &= ~NO_RECV_IV;
 356                 encrypt_send_keyid(DIR_ENCRYPT, "\0", 1, 1);
 357                 break;
 358
 359         case FB64_IV_BAD:
 360                 memset(fbp->temp_feed, 0, sizeof(Block));
 361                 fb64_stream_iv(fbp->temp_feed, &fbp->streams[DIR_ENCRYPT-1]);
 362                 state = FAILED;
 363                 break;
 364
 365         default:
 366                 if (encrypt_debug_mode) {
 367                         printf("Unknown option type: %d\r\n", data[-1]);
 368                         printd(data, cnt);
 369                         printf("\r\n");
 370                 }
 371                 /* FALL THROUGH */
 372         failure:
 373                 state = FAILED;
 374                 break;
 375         }
 376         return(fbp->state[DIR_ENCRYPT-1] = state);
 377 }
 378
 379 void
 380 cfb64_session(Session_Key *key, int server)
 381 {
 382         fb64_session(key, server, &fb[CFB]);
 383 }
 384
 385 void
 386 ofb64_session(Session_Key *key, int server)
 387 {
 388         fb64_session(key, server, &fb[OFB]);
 389 }
 390
 391 static void
 392 fb64_session(Session_Key *key, int server, struct fb *fbp)
 393 {
 394         if (!key || key->type != SK_DES) {
 395                 if (encrypt_debug_mode)
 396                         printf("Can't set krbdes's session key (%d != %d)\r\n",
 397                                 key ? key->type : -1, SK_DES);
 398                 return;
 399         }
 400         memmove((void *)fbp->krbdes_key, (void *)key->data, sizeof(Block));
 401
 402         fb64_stream_key(fbp->krbdes_key, &fbp->streams[DIR_ENCRYPT-1]);
 403         fb64_stream_key(fbp->krbdes_key, &fbp->streams[DIR_DECRYPT-1]);
 404
 405         if (fbp->once == 0) {
 406                 des_set_random_generator_seed(fbp->krbdes_key);
 407                 fbp->once = 1;
 408         }
 409         des_key_sched(fbp->krbdes_key, fbp->krbdes_sched);
 410         /*
 411          * Now look to see if krbdes_start() was was waiting for
 412          * the key to show up.  If so, go ahead an call it now
 413          * that we have the key.
 414          */
 415         if (fbp->need_start) {
 416                 fbp->need_start = 0;
 417                 fb64_start(fbp, DIR_ENCRYPT, server);
 418         }
 419 }
 420
 421 /*
 422  * We only accept a keyid of 0.  If we get a keyid of
 423  * 0, then mark the state as SUCCESS.
 424  */
 425 int
 426 cfb64_keyid(int dir, unsigned char *kp, int *lenp)
 427 {
 428         return(fb64_keyid(dir, kp, lenp, &fb[CFB]));
 429 }
 430
 431 int
 432 ofb64_keyid(int dir, unsigned char *kp, int *lenp)
 433 {
 434         return(fb64_keyid(dir, kp, lenp, &fb[OFB]));
 435 }
 436
 437 int
 438 fb64_keyid(int dir, unsigned char *kp, int *lenp, struct fb *fbp)
 439 {
 440         int state = fbp->state[dir-1];
 441
 442         if (*lenp != 1 || (*kp != '\0')) {
 443                 *lenp = 0;
 444                 return(state);
 445         }
 446
 447         if (state == FAILED)
 448                 state = IN_PROGRESS;
 449
 450         state &= ~NO_KEYID;
 451
 452         return(fbp->state[dir-1] = state);
 453 }
 454
 455 void
 456 fb64_printsub(unsigned char *data, int cnt, unsigned char *buf, int buflen, const char *type)
 457 {
 458         char lbuf[32];
 459         int i;
 460         char *cp;
 461
 462         buf[buflen-1] = '\0';           /* make sure it's NULL terminated */
 463         buflen -= 1;
 464
 465         switch(data[2]) {
 466         case FB64_IV:
 467                 sprintf(lbuf, "%s_IV", type);
 468                 cp = lbuf;
 469                 goto common;
 470
 471         case FB64_IV_OK:
 472                 sprintf(lbuf, "%s_IV_OK", type);
 473                 cp = lbuf;
 474                 goto common;
 475
 476         case FB64_IV_BAD:
 477                 sprintf(lbuf, "%s_IV_BAD", type);
 478                 cp = lbuf;
 479                 goto common;
 480
 481         default:
 482                 sprintf(lbuf, " %d (unknown)", data[2]);
 483                 cp = lbuf;
 484         common:
 485                 for (; (buflen > 0) && (*buf = *cp++); buf++)
 486                         buflen--;
 487                 for (i = 3; i < cnt; i++) {
 488                         sprintf(lbuf, " %d", data[i]);
 489                         for (cp = lbuf; (buflen > 0) && (*buf = *cp++); buf++)
 490                                 buflen--;
 491                 }
 492                 break;
 493         }
 494 }
 495
 496 void
 497 cfb64_printsub(unsigned char *data, int cnt, unsigned char *buf, int buflen)
 498 {
 499         fb64_printsub(data, cnt, buf, buflen, "CFB64");
 500 }
 501
 502 void
 503 ofb64_printsub(unsigned char *data, int cnt, unsigned char *buf, int buflen)
 504 {
 505         fb64_printsub(data, cnt, buf, buflen, "OFB64");
 506 }
 507
 508 void
 509 fb64_stream_iv(Block seed, struct stinfo *stp)
 510 {
 511
 512         memmove((void *)stp->str_iv, (void *)seed, sizeof(Block));
 513         memmove((void *)stp->str_output, (void *)seed, sizeof(Block));
 514
 515         des_key_sched(stp->str_ikey, stp->str_sched);
 516
 517         stp->str_index = sizeof(Block);
 518 }
 519
 520 void
 521 fb64_stream_key(Block key, struct stinfo *stp)
 522 {
 523         memmove((void *)stp->str_ikey, (void *)key, sizeof(Block));
 524         des_key_sched(key, stp->str_sched);
 525
 526         memmove((void *)stp->str_output, (void *)stp->str_iv, sizeof(Block));
 527
 528         stp->str_index = sizeof(Block);
 529 }
 530
 531 /*
 532  * DES 64 bit Cipher Feedback
 533  *
 534  *     key --->+-----+
 535  *          +->| DES |--+
 536  *          |  +-----+  |
 537  *          |           v
 538  *  INPUT --(--------->(+)+---> DATA
 539  *          |             |
 540  *          +-------------+
 541  *
 542  *
 543  * Given:
 544  *      iV: Initial vector, 64 bits (8 bytes) long.
 545  *      Dn: the nth chunk of 64 bits (8 bytes) of data to encrypt (decrypt).
 546  *      On: the nth chunk of 64 bits (8 bytes) of encrypted (decrypted) output.
 547  *
 548  *      V0 = DES(iV, key)
 549  *      On = Dn ^ Vn
 550  *      V(n+1) = DES(On, key)
 551  */
 552
 553 void
 554 cfb64_encrypt(unsigned char *s, int c)
 555 {
 556         struct stinfo *stp = &fb[CFB].streams[DIR_ENCRYPT-1];
 557         int idx;
 558
 559         idx = stp->str_index;
 560         while (c-- > 0) {
 561                 if (idx == sizeof(Block)) {
 562                         Block b;
 563                         des_ecb_encrypt((Block *)stp->str_output, (Block *)b, stp->str_sched, 1);
 564                         memmove((void *)stp->str_feed, (void *)b, sizeof(Block));
 565                         idx = 0;
 566                 }
 567
 568                 /* On encryption, we store (feed ^ data) which is cypher */
 569                 *s = stp->str_output[idx] = (stp->str_feed[idx] ^ *s);
 570                 s++;
 571                 idx++;
 572         }
 573         stp->str_index = idx;
 574 }
 575
 576 int
 577 cfb64_decrypt(int data)
 578 {
 579         struct stinfo *stp = &fb[CFB].streams[DIR_DECRYPT-1];
 580         int idx;
 581
 582         if (data == -1) {
 583                 /*
 584                  * Back up one byte.  It is assumed that we will
 585                  * never back up more than one byte.  If we do, this
 586                  * may or may not work.
 587                  */
 588                 if (stp->str_index)
 589                         --stp->str_index;
 590                 return(0);
 591         }
 592
 593         idx = stp->str_index++;
 594         if (idx == sizeof(Block)) {
 595                 Block b;
 596                 des_ecb_encrypt((Block *)stp->str_output, (Block *)b, stp->str_sched, 1);
 597                 memmove((void *)stp->str_feed, (void *)b, sizeof(Block));
 598                 stp->str_index = 1;     /* Next time will be 1 */
 599                 idx = 0;                /* But now use 0 */
 600         }
 601
 602         /* On decryption we store (data) which is cypher. */
 603         stp->str_output[idx] = data;
 604         return(data ^ stp->str_feed[idx]);
 605 }
 606
 607 /*
 608  * DES 64 bit Output Feedback
 609  *
 610  * key --->+-----+
 611  *      +->| DES |--+
 612  *      |  +-----+  |
 613  *      +-----------+
 614  *                  v
 615  *  INPUT -------->(+) ----> DATA
 616  *
 617  * Given:
 618  *      iV: Initial vector, 64 bits (8 bytes) long.
 619  *      Dn: the nth chunk of 64 bits (8 bytes) of data to encrypt (decrypt).
 620  *      On: the nth chunk of 64 bits (8 bytes) of encrypted (decrypted) output.
 621  *
 622  *      V0 = DES(iV, key)
 623  *      V(n+1) = DES(Vn, key)
 624  *      On = Dn ^ Vn
 625  */
 626 void
 627 ofb64_encrypt(unsigned char *s, int c)
 628 {
 629         struct stinfo *stp = &fb[OFB].streams[DIR_ENCRYPT-1];
 630         int idx;
 631
 632         idx = stp->str_index;
 633         while (c-- > 0) {
 634                 if (idx == sizeof(Block)) {
 635                         Block b;
 636                         des_ecb_encrypt((Block *)stp->str_feed, (Block *)b, stp->str_sched, 1);
 637                         memmove((void *)stp->str_feed, (void *)b, sizeof(Block));
 638                         idx = 0;
 639                 }
 640                 *s++ ^= stp->str_feed[idx];
 641                 idx++;
 642         }
 643         stp->str_index = idx;
 644 }
 645
 646 int
 647 ofb64_decrypt(int data)
 648 {
 649         struct stinfo *stp = &fb[OFB].streams[DIR_DECRYPT-1];
 650         int idx;
 651
 652         if (data == -1) {
 653                 /*
 654                  * Back up one byte.  It is assumed that we will
 655                  * never back up more than one byte.  If we do, this
 656                  * may or may not work.
 657                  */
 658                 if (stp->str_index)
 659                         --stp->str_index;
 660                 return(0);
 661         }
 662
 663         idx = stp->str_index++;
 664         if (idx == sizeof(Block)) {
 665                 Block b;
 666                 des_ecb_encrypt((Block *)stp->str_feed, (Block *)b, stp->str_sched, 1);
 667                 memmove((void *)stp->str_feed, (void *)b, sizeof(Block));
 668                 stp->str_index = 1;     /* Next time will be 1 */
 669                 idx = 0;                /* But now use 0 */
 670         }
 671
 672         return(data ^ stp->str_feed[idx]);
 673 }
 674 # endif /* AUTHENTICATION */
 675 #endif  /* ENCRYPTION */