mdw@git.distorted.org.uk Git - tripe/blob - server/keyset.c

   1 /* -*-c-*-
   2  *
   3  * Handling of symmetric keysets
   4  *
   5  * (c) 2001 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Trivial IP Encryption (TrIPE).
  11  *
  12  * TrIPE is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * TrIPE is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with TrIPE; if not, write to the Free Software Foundation,
  24  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 /*----- Header files ------------------------------------------------------*/
  28
  29 #include "tripe.h"
  30
  31 /*----- Handy macros ------------------------------------------------------*/
  32
  33 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
  34
  35 #define SEQSZ 4                         /* Size of sequence number packet */
  36
  37 /*----- Low-level packet encryption and decryption ------------------------*/
  38
  39 /* --- Encrypted data format --- *
  40  *
  41  * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%.  We first
  42  * compute
  43  *
  44  *   %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
  45  *
  46  * as the CBC-ciphertext of %$p_i$%, and then
  47  *
  48  *   %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
  49  *
  50  * as a MAC on the %%\emph{ciphertext}%%.  The message sent is then the pair
  51  * %$(\sigma_i, c_i)$%.  This construction is provably secure in the NM-CCA
  52  * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
  53  * [Bellare and Namprempre].
  54  *
  55  * This also ensures that, assuming the key is good, we have a secure channel
  56  * [Krawczyk].  Actually, [Krawczyk] shows that, if the cipher is either a
  57  * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
  58  * then-encrypt scheme and still have a secure channel.  However, I like the
  59  * NM-CCA guarantee from [Bellare and Namprempre].  I'm less worried about
  60  * the Horton Principle [Wagner and Schneier].
  61  */
  62
  63 /* --- @doencrypt@ --- *
  64  *
  65  * Arguments:   @keyset *ks@ = pointer to keyset to use
  66  *              @unsigned ty@ = type of message this is
  67  *              @buf *b@ = pointer to an input buffer
  68  *              @buf *bb@ = pointer to an output buffer
  69  *
  70  * Returns:     Zero if OK; @KSERR_REGEN@ if it's time to generate new keys.
  71  *              Also returns zero if there was insufficient buffer space, but
  72  *              the buffer is broken in this case.
  73  *
  74  * Use:         Encrypts a message with the given key.  We assume that the
  75  *              keyset is OK to use.
  76  */
  77
  78 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
  79 {
  80   ghash *h;
  81   gcipher *c = ks->cout;
  82   const octet *p = BCUR(b);
  83   size_t sz = BLEFT(b);
  84   octet *qmac, *qseq, *qiv, *qpk;
  85   uint32 oseq;
  86   size_t ivsz = GC_CLASS(c)->blksz;
  87   size_t tagsz = ks->tagsz;
  88   size_t osz, nsz;
  89   octet t[4];
  90   int rc = 0;
  91
  92   /* --- Allocate the required buffer space --- */
  93
  94   if (buf_ensure(bb, tagsz + SEQSZ + ivsz + sz))
  95     return (0); /* Caution! */
  96   qmac = BCUR(bb); qseq = qmac + tagsz; qiv = qseq + SEQSZ; qpk = qiv + ivsz;
  97   BSTEP(bb, tagsz + SEQSZ + ivsz + sz);
  98   STORE32(t, ty);
  99
 100   oseq = ks->oseq++; STORE32(qseq, oseq);
 101   IF_TRACING(T_KEYSET, {
 102     trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
 103           (unsigned long)oseq, ks->seq);
 104     trace_block(T_CRYPTO, "crypto: plaintext packet", p, sz);
 105   })
 106
 107   /* --- Encrypt the packet --- */
 108
 109   if (ivsz) {
 110     rand_get(RAND_GLOBAL, qiv, ivsz);
 111     GC_SETIV(c, qiv);
 112     IF_TRACING(T_KEYSET, {
 113       trace_block(T_CRYPTO, "crypto: initialization vector", qiv, ivsz);
 114     })
 115   }
 116   GC_ENCRYPT(c, p, qpk, sz);
 117   IF_TRACING(T_KEYSET, {
 118     trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
 119   })
 120
 121   /* --- Now compute the MAC --- */
 122
 123   if (tagsz) {
 124     h = GM_INIT(ks->mout);
 125     GH_HASH(h, t, sizeof(t));
 126     GH_HASH(h, qseq, SEQSZ + ivsz + sz);
 127     memcpy(qmac, GH_DONE(h, 0), tagsz);
 128     GH_DESTROY(h);
 129     IF_TRACING(T_KEYSET, {
 130       trace_block(T_CRYPTO, "crypto: computed MAC", qmac, tagsz);
 131     })
 132   }
 133
 134   /* --- Deduct the packet size from the key's data life --- */
 135
 136   osz = ks->sz_exp;
 137   if (osz > sz)
 138     nsz = osz - sz;
 139   else
 140     nsz = 0;
 141   if (osz >= ks->sz_regen && ks->sz_regen > nsz) {
 142     T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
 143              "forcing exchange", ks->seq); )
 144     rc = KSERR_REGEN;
 145   }
 146   ks->sz_exp = nsz;
 147   return (rc);
 148 }
 149
 150 /* --- @dodecrypt@ --- *
 151  *
 152  * Arguments:   @keyset *ks@ = pointer to keyset to use
 153  *              @unsigned ty@ = expected type code
 154  *              @buf *b@ = pointer to an input buffer
 155  *              @buf *bb@ = pointer to an output buffer
 156  *              @uint32 *seq@ = where to store the sequence number
 157  *
 158  * Returns:     Zero on success; @KSERR_DECRYPT@ on failure.
 159  *
 160  * Use:         Attempts to decrypt a message with the given key.  No other
 161  *              checking (e.g., sequence number checks) is performed.  We
 162  *              assume that the keyset is OK to use, and that there is
 163  *              sufficient output buffer space reserved.  If the decryption
 164  *              is successful, the buffer pointer is moved past the decrypted
 165  *              packet, and the packet's sequence number is stored in @*seq@.
 166  */
 167
 168 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
 169 {
 170   const octet *pmac, *piv, *pseq, *ppk;
 171   size_t psz = BLEFT(b);
 172   size_t sz;
 173   octet *q = BCUR(bb);
 174   ghash *h;
 175   gcipher *c = ks->cin;
 176   size_t ivsz = GC_CLASS(c)->blksz;
 177   size_t tagsz = ks->tagsz;
 178   octet *mac;
 179   int eq;
 180   octet t[4];
 181
 182   /* --- Break up the packet into its components --- */
 183
 184   if (psz < ivsz + SEQSZ + tagsz) {
 185     T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
 186     return (KSERR_MALFORMED);
 187   }
 188   sz = psz - ivsz - SEQSZ - tagsz;
 189   pmac = BCUR(b); pseq = pmac + tagsz; piv = pseq + SEQSZ; ppk = piv + ivsz;
 190   STORE32(t, ty);
 191
 192   IF_TRACING(T_KEYSET, {
 193     trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
 194     trace_block(T_CRYPTO, "crypto: ciphertext packet", ppk, sz);
 195   })
 196
 197   /* --- Verify the MAC on the packet --- */
 198
 199   if (tagsz) {
 200     h = GM_INIT(ks->min);
 201     GH_HASH(h, t, sizeof(t));
 202     GH_HASH(h, pseq, SEQSZ + ivsz + sz);
 203     mac = GH_DONE(h, 0);
 204     eq = !memcmp(mac, pmac, tagsz);
 205     IF_TRACING(T_KEYSET, {
 206       trace_block(T_CRYPTO, "crypto: computed MAC", mac, tagsz);
 207     })
 208     GH_DESTROY(h);
 209     if (!eq) {
 210       IF_TRACING(T_KEYSET, {
 211         trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
 212         trace_block(T_CRYPTO, "crypto: expected MAC", pmac, tagsz);
 213       })
 214       return (KSERR_DECRYPT);
 215     }
 216   }
 217
 218   /* --- Decrypt the packet --- */
 219
 220   if (ivsz) {
 221     GC_SETIV(c, piv);
 222     IF_TRACING(T_KEYSET, {
 223       trace_block(T_CRYPTO, "crypto: initialization vector", piv, ivsz);
 224     })
 225   }
 226   GC_DECRYPT(c, ppk, q, sz);
 227   if (seq)
 228     *seq = LOAD32(pseq);
 229   IF_TRACING(T_KEYSET, {
 230     trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
 231           (unsigned long)LOAD32(pseq));
 232     trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
 233   })
 234   BSTEP(bb, sz);
 235   return (0);
 236 }
 237
 238 /*----- Operations on a single keyset -------------------------------------*/
 239
 240 /* --- @ks_drop@ --- *
 241  *
 242  * Arguments:   @keyset *ks@ = pointer to a keyset
 243  *
 244  * Returns:     ---
 245  *
 246  * Use:         Decrements a keyset's reference counter.  If the counter hits
 247  *              zero, the keyset is freed.
 248  */
 249
 250 void ks_drop(keyset *ks)
 251 {
 252   if (--ks->ref)
 253     return;
 254   GC_DESTROY(ks->cin);
 255   GC_DESTROY(ks->cout);
 256   GM_DESTROY(ks->min);
 257   GM_DESTROY(ks->mout);
 258   DESTROY(ks);
 259 }
 260
 261 /* --- @ks_gen@ --- *
 262  *
 263  * Arguments:   @const void *k@ = pointer to key material
 264  *              @size_t x, y, z@ = offsets into key material (see below)
 265  *              @peer *p@ = pointer to peer information
 266  *
 267  * Returns:     A pointer to the new keyset.
 268  *
 269  * Use:         Derives a new keyset from the given key material.  The
 270  *              offsets @x@, @y@ and @z@ separate the key material into three
 271  *              parts.  Between the @k@ and @k + x@ is `my' contribution to
 272  *              the key material; between @k + x@ and @k + y@ is `your'
 273  *              contribution; and between @k + y@ and @k + z@ is a shared
 274  *              value we made together.  These are used to construct two
 275  *              pairs of symmetric keys.  Each pair consists of an encryption
 276  *              key and a message authentication key.  One pair is used for
 277  *              outgoing messages, the other for incoming messages.
 278  *
 279  *              The new key is marked so that it won't be selected for output
 280  *              by @ksl_encrypt@.  You can still encrypt data with it by
 281  *              calling @ks_encrypt@ directly.
 282  */
 283
 284 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
 285 {
 286   ghash *h;
 287   const octet *hh;
 288   keyset *ks = CREATE(keyset);
 289   time_t now = time(0);
 290   const octet *pp = k;
 291   T( static unsigned seq = 0; )
 292
 293   T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
 294
 295   /* --- Construct the various keys --- *
 296    *
 297    * This is done with macros, because it's quite tedious.
 298    */
 299
 300 #define MINE GH_HASH(h, pp, x)
 301 #define YOURS GH_HASH(h, pp + x, y - x)
 302 #define OURS GH_HASH(h, pp + y, z - y)
 303
 304 #define HASH_in MINE; YOURS; OURS
 305 #define HASH_out YOURS; MINE; OURS
 306 #define INIT_c(k) GC_INIT(algs.c, (k), algs.cksz)
 307 #define INIT_m(k) GM_KEY(algs.m, (k), algs.mksz)
 308 #define STR_c "encryption"
 309 #define STR_m "integrity"
 310 #define STR_in "incoming"
 311 #define STR_out "outgoing"
 312
 313 #define SETKEY(a, dir) do {                                             \
 314   h = GH_INIT(algs.h);                                                  \
 315   HASH_STRING(h, "tripe-" STR_##a);                                     \
 316   HASH_##dir;                                                           \
 317   hh = GH_DONE(h, 0);                                                   \
 318   IF_TRACING(T_KEYSET, {                                                \
 319     trace_block(T_CRYPTO, "crypto: " STR_##dir " key " STR_##a,         \
 320                 hh, algs.a##ksz);                                       \
 321   })                                                                    \
 322   ks->a##dir = INIT_##a(hh);                                            \
 323   GH_DESTROY(h);                                                        \
 324 } while (0)
 325
 326   SETKEY(c, in); SETKEY(c, out);
 327   SETKEY(m, in); SETKEY(m, out);
 328
 329 #undef MINE
 330 #undef YOURS
 331 #undef OURS
 332 #undef STR_c
 333 #undef STR_m
 334 #undef STR_in
 335 #undef STR_out
 336 #undef INIT_c
 337 #undef INIT_m
 338 #undef HASH_in
 339 #undef HASH_out
 340 #undef SETKEY
 341
 342   T( ks->seq = seq++; )
 343   ks->ref = 1;
 344   ks->t_exp = now + T_EXP;
 345   ks->sz_exp = algs.expsz;
 346   ks->sz_regen = algs.expsz/2;
 347   ks->oseq = 0;
 348   seq_reset(&ks->iseq);
 349   ks->next = 0;
 350   ks->p = p;
 351   ks->f = KSF_LISTEN;
 352   ks->tagsz = algs.tagsz;
 353   return (ks);
 354 }
 355
 356 /* --- @ks_activate@ --- *
 357  *
 358  * Arguments:   @keyset *ks@ = pointer to a keyset
 359  *
 360  * Returns:     ---
 361  *
 362  * Use:         Activates a keyset, so that it can be used for encrypting
 363  *              outgoing messages.
 364  */
 365
 366 void ks_activate(keyset *ks)
 367 {
 368   if (ks->f & KSF_LISTEN) {
 369     T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
 370     ks->f &= ~KSF_LISTEN;
 371   }
 372 }
 373
 374 /* --- @ks_encrypt@ --- *
 375  *
 376  * Arguments:   @keyset *ks@ = pointer to a keyset
 377  *              @unsigned ty@ = message type
 378  *              @buf *b@ = pointer to input buffer
 379  *              @buf *bb@ = pointer to output buffer
 380  *
 381  * Returns:     Zero if successful; @KSERR_REGEN@ if we should negotiate a
 382  *              new key; @KSERR_NOKEYS@ if the key is not usable.  Also
 383  *              returns zero if there was insufficient buffer (but the output
 384  *              buffer is broken in this case).
 385  *
 386  * Use:         Encrypts a block of data using the key.  Note that the `key
 387  *              ought to be replaced' notification is only ever given once
 388  *              for each key.  Also note that this call forces a keyset to be
 389  *              used even if it's marked as not for data output.
 390  */
 391
 392 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
 393 {
 394   time_t now = time(0);
 395
 396   if (!KEYOK(ks, now)) {
 397     buf_break(bb);
 398     return (KSERR_NOKEYS);
 399   }
 400   return (doencrypt(ks, ty, b, bb));
 401 }
 402
 403 /* --- @ks_decrypt@ --- *
 404  *
 405  * Arguments:   @keyset *ks@ = pointer to a keyset
 406  *              @unsigned ty@ = expected type code
 407  *              @buf *b@ = pointer to an input buffer
 408  *              @buf *bb@ = pointer to an output buffer
 409  *
 410  * Returns:     Zero on success; @KSERR_...@ on failure.  Also returns
 411  *              zero if there was insufficient buffer (but the output buffer
 412  *              is broken in this case).
 413  *
 414  * Use:         Attempts to decrypt a message using a given key.  Note that
 415  *              requesting decryption with a key directly won't clear a
 416  *              marking that it's not for encryption.
 417  */
 418
 419 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
 420 {
 421   time_t now = time(0);
 422   uint32 seq;
 423   int err;
 424
 425   if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
 426   if (buf_ensure(bb, BLEN(b))) return (0);
 427   if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
 428   if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
 429   return (0);
 430 }
 431
 432 /*----- Keyset list handling ----------------------------------------------*/
 433
 434 /* --- @ksl_free@ --- *
 435  *
 436  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 437  *
 438  * Returns:     ---
 439  *
 440  * Use:         Frees (releases references to) all of the keys in a keyset.
 441  */
 442
 443 void ksl_free(keyset **ksroot)
 444 {
 445   keyset *ks, *ksn;
 446   for (ks = *ksroot; ks; ks = ksn) {
 447     ksn = ks->next;
 448     ks->f &= ~KSF_LINK;
 449     ks_drop(ks);
 450   }
 451 }
 452
 453 /* --- @ksl_link@ --- *
 454  *
 455  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 456  *              @keyset *ks@ = pointer to a keyset
 457  *
 458  * Returns:     ---
 459  *
 460  * Use:         Links a keyset into a list.  A keyset can only be on one list
 461  *              at a time.  Bad things happen otherwise.
 462  */
 463
 464 void ksl_link(keyset **ksroot, keyset *ks)
 465 {
 466   assert(!(ks->f & KSF_LINK));
 467   ks->next = *ksroot;
 468   *ksroot = ks;
 469   ks->f |= KSF_LINK;
 470   ks->ref++;
 471 }
 472
 473 /* --- @ksl_prune@ --- *
 474  *
 475  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 476  *
 477  * Returns:     ---
 478  *
 479  * Use:         Prunes the keyset list by removing keys which mustn't be used
 480  *              any more.
 481  */
 482
 483 void ksl_prune(keyset **ksroot)
 484 {
 485   time_t now = time(0);
 486
 487   while (*ksroot) {
 488     keyset *ks = *ksroot;
 489
 490     if (ks->t_exp <= now) {
 491       T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
 492                ks->seq); )
 493       goto kill;
 494     } else if (ks->sz_exp == 0) {
 495       T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
 496                ks->seq); )
 497       goto kill;
 498     } else {
 499       ksroot = &ks->next;
 500       continue;
 501     }
 502
 503   kill:
 504     *ksroot = ks->next;
 505     ks->f &= ~KSF_LINK;
 506     ks_drop(ks);
 507   }
 508 }
 509
 510 /* --- @ksl_encrypt@ --- *
 511  *
 512  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 513  *              @unsigned ty@ = message type
 514  *              @buf *b@ = pointer to input buffer
 515  *              @buf *bb@ = pointer to output buffer
 516  *
 517  * Returns:     Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
 518  *              new key; @KSERR_NOKEYS@ if there are no suitable keys
 519  *              available.  Also returns zero if there was insufficient
 520  *              buffer space (but the output buffer is broken in this case).
 521  *
 522  * Use:         Encrypts a packet.
 523  */
 524
 525 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
 526 {
 527   time_t now = time(0);
 528   keyset *ks = *ksroot;
 529
 530   for (;;) {
 531     if (!ks) {
 532       T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
 533       buf_break(bb);
 534       return (KSERR_NOKEYS);
 535     }
 536     if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
 537       break;
 538     ks = ks->next;
 539   }
 540
 541   return (doencrypt(ks, ty, b, bb));
 542 }
 543
 544 /* --- @ksl_decrypt@ --- *
 545  *
 546  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 547  *              @unsigned ty@ = expected type code
 548  *              @buf *b@ = pointer to input buffer
 549  *              @buf *bb@ = pointer to output buffer
 550  *
 551  * Returns:     Zero on success; @KSERR_DECRYPT@ on failure.  Also returns
 552  *              zero if there was insufficient buffer (but the output buffer
 553  *              is broken in this case).
 554  *
 555  * Use:         Decrypts a packet.
 556  */
 557
 558 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
 559 {
 560   time_t now = time(0);
 561   keyset *ks;
 562   uint32 seq;
 563   int err;
 564
 565   if (buf_ensure(bb, BLEN(b)))
 566     return (0);
 567
 568   for (ks = *ksroot; ks; ks = ks->next) {
 569     if (!KEYOK(ks, now))
 570       continue;
 571     if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
 572       if (ks->f & KSF_LISTEN) {
 573         T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
 574                  ks->seq); )
 575         ks->f &= ~KSF_LISTEN;
 576       }
 577       if (seq_check(&ks->iseq, seq, "SYMM"))
 578         return (KSERR_SEQ);
 579       else
 580         return (0);
 581     }
 582     if (err != KSERR_DECRYPT) return (err);
 583   }
 584   T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
 585   return (KSERR_DECRYPT);
 586 }
 587
 588 /*----- That's all, folks -------------------------------------------------*/