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 it under
  13  * the terms of the GNU General Public License as published by the Free
  14  * Software Foundation; either version 3 of the License, or (at your
  15  * option) any later version.
  16  *
  17  * TrIPE is distributed in the hope that it will be useful, but WITHOUT
  18  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  19  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  20  * for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with TrIPE.  If not, see <https://www.gnu.org/licenses/>.
  24  */
  25
  26 /*----- Header files ------------------------------------------------------*/
  27
  28 #include "tripe.h"
  29
  30 /*----- Handy macros ------------------------------------------------------*/
  31
  32 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
  33
  34 /*----- Low-level packet encryption and decryption ------------------------*/
  35
  36 /* --- Encrypted data format --- *
  37  *
  38  * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%.  We first
  39  * compute
  40  *
  41  *   %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
  42  *
  43  * as the CBC-ciphertext of %$p_i$%, and then
  44  *
  45  *   %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
  46  *
  47  * as a MAC on the %%\emph{ciphertext}%%.  The message sent is then the pair
  48  * %$(\sigma_i, c_i)$%.  This construction is provably secure in the NM-CCA
  49  * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
  50  * [Bellare and Namprempre].
  51  *
  52  * This also ensures that, assuming the key is good, we have a secure channel
  53  * [Krawczyk].  Actually, [Krawczyk] shows that, if the cipher is either a
  54  * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
  55  * then-encrypt scheme and still have a secure channel.  However, I like the
  56  * NM-CCA guarantee from [Bellare and Namprempre].  I'm less worried about
  57  * the Horton Principle [Wagner and Schneier].
  58  */
  59
  60 /* --- @doencrypt@ --- *
  61  *
  62  * Arguments:   @keyset *ks@ = pointer to keyset to use
  63  *              @unsigned ty@ = type of message this is
  64  *              @buf *b@ = pointer to an input buffer
  65  *              @buf *bb@ = pointer to an output buffer
  66  *
  67  * Returns:     Zero if OK; @KSERR_REGEN@ if it's time to generate new keys.
  68  *              Also returns zero if there was insufficient buffer space, but
  69  *              the buffer is broken in this case.
  70  *
  71  * Use:         Encrypts a message with the given key.  We assume that the
  72  *              keyset is OK to use.
  73  */
  74
  75 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
  76 {
  77   int rc;
  78   size_t sz = BLEFT(b);
  79   size_t osz, nsz;
  80
  81   /* --- Initial tracing --- */
  82
  83   IF_TRACING(T_KEYSET, {
  84     trace(T_KEYSET,
  85           "keyset: encrypting packet %lu (type 0x%02x) using keyset %u",
  86           (unsigned long)ks->oseq, ty, ks->seq);
  87     trace_block(T_CRYPTO, "crypto: plaintext packet", BCUR(b), sz);
  88   })
  89
  90   /* --- Apply the bulk-crypto transformation --- */
  91
  92   rc = ks->bulk->ops->encrypt(ks->bulk, ty, b, bb, ks->oseq);
  93   if (rc || !BOK(bb)) return (rc);
  94   ks->oseq++;
  95
  96   /* --- Do the necessary accounting for data volume --- */
  97
  98   osz = ks->sz_exp;
  99   nsz = osz > sz ? osz - sz : 0;
 100   if (osz >= ks->sz_regen && ks->sz_regen > nsz) {
 101     T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
 102              "forcing exchange", ks->seq); )
 103     rc = KSERR_REGEN;
 104   }
 105   ks->sz_exp = nsz;
 106
 107   /* --- We're done --- */
 108
 109   return (rc);
 110 }
 111
 112 /* --- @dodecrypt@ --- *
 113  *
 114  * Arguments:   @keyset *ks@ = pointer to keyset to use
 115  *              @unsigned ty@ = expected type code
 116  *              @buf *b@ = pointer to an input buffer
 117  *              @buf *bb@ = pointer to an output buffer
 118  *              @uint32 *seq@ = where to store the sequence number
 119  *
 120  * Returns:     Zero on success; @KSERR_DECRYPT@ on failure.
 121  *
 122  * Use:         Attempts to decrypt a message with the given key.  No other
 123  *              checking (e.g., sequence number checks) is performed.  We
 124  *              assume that the keyset is OK to use, and that there is
 125  *              sufficient output buffer space reserved.  If the decryption
 126  *              is successful, the buffer pointer is moved past the decrypted
 127  *              packet, and the packet's sequence number is stored in @*seq@.
 128  */
 129
 130 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
 131 {
 132   const octet *q = BCUR(bb);
 133   int rc;
 134
 135   IF_TRACING(T_KEYSET, {
 136     trace(T_KEYSET,
 137           "keyset: try decrypting packet (type 0x%02x) using keyset %u",
 138           ty, ks->seq);
 139     trace_block(T_CRYPTO, "crypto: ciphertext packet", BCUR(b), BLEFT(b));
 140   })
 141
 142   rc = ks->bulk->ops->decrypt(ks->bulk, ty, b, bb, seq);
 143   if (rc) return (rc);
 144
 145   IF_TRACING(T_KEYSET, {
 146     trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
 147           (unsigned long)*seq);
 148     trace_block(T_CRYPTO, "crypto: decrypted packet", q, BCUR(bb) - q);
 149   })
 150   return (0);
 151 }
 152
 153 /*----- Operations on a single keyset -------------------------------------*/
 154
 155 /* --- @ks_drop@ --- *
 156  *
 157  * Arguments:   @keyset *ks@ = pointer to a keyset
 158  *
 159  * Returns:     ---
 160  *
 161  * Use:         Decrements a keyset's reference counter.  If the counter hits
 162  *              zero, the keyset is freed.
 163  */
 164
 165 void ks_drop(keyset *ks)
 166 {
 167   if (--ks->ref) return;
 168   ks->bulk->ops->freectx(ks->bulk);
 169   DESTROY(ks);
 170 }
 171
 172 /* --- @ks_gen@ --- *
 173  *
 174  * Arguments:   @deriveargs *a@ = key derivation parameters (modified)
 175  *              @peer *p@ = pointer to peer information
 176  *
 177  * Returns:     A pointer to the new keyset.
 178  *
 179  * Use:         Derives a new keyset from the given key material.  This will
 180  *              set the @what@, @f@, and @hc@ members in @*a@; other members
 181  *              must be filled in by the caller.
 182  *
 183  *              The new key is marked so that it won't be selected for output
 184  *              by @ksl_encrypt@.  You can still encrypt data with it by
 185  *              calling @ks_encrypt@ directly.
 186  */
 187
 188 keyset *ks_gen(deriveargs *a, peer *p)
 189 {
 190   keyset *ks = CREATE(keyset);
 191   time_t now = time(0);
 192   const algswitch *algs = &p->kx.kpriv->algs;
 193   T( static unsigned seq = 0; )
 194
 195   T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
 196
 197   a->what = "tripe-"; a->f = DF_IN | DF_OUT; a->hc = algs->h;
 198   ks->bulk = algs->bulk->ops->genkeys(algs->bulk, a);
 199   ks->bulk->ops = algs->bulk->ops;
 200
 201   T( ks->seq = seq++; )
 202   ks->ref = 1;
 203   ks->t_exp = now + T_EXP;
 204   ks->sz_exp = algs->bulk->ops->expsz(algs->bulk);
 205   ks->sz_regen = ks->sz_exp/2;
 206   ks->oseq = 0;
 207   seq_reset(&ks->iseq);
 208   ks->next = 0;
 209   ks->p = p;
 210   ks->f = KSF_LISTEN;
 211   return (ks);
 212 }
 213
 214 /* --- @ks_activate@ --- *
 215  *
 216  * Arguments:   @keyset *ks@ = pointer to a keyset
 217  *
 218  * Returns:     ---
 219  *
 220  * Use:         Activates a keyset, so that it can be used for encrypting
 221  *              outgoing messages.
 222  */
 223
 224 void ks_activate(keyset *ks)
 225 {
 226   if (ks->f & KSF_LISTEN) {
 227     T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
 228     ks->f &= ~KSF_LISTEN;
 229   }
 230 }
 231
 232 /* --- @ks_encrypt@ --- *
 233  *
 234  * Arguments:   @keyset *ks@ = pointer to a keyset
 235  *              @unsigned ty@ = message type
 236  *              @buf *b@ = pointer to input buffer
 237  *              @buf *bb@ = pointer to output buffer
 238  *
 239  * Returns:     Zero if successful; @KSERR_REGEN@ if we should negotiate a
 240  *              new key; @KSERR_NOKEYS@ if the key is not usable.  Also
 241  *              returns zero if there was insufficient buffer (but the output
 242  *              buffer is broken in this case).
 243  *
 244  * Use:         Encrypts a block of data using the key.  Note that the `key
 245  *              ought to be replaced' notification is only ever given once
 246  *              for each key.  Also note that this call forces a keyset to be
 247  *              used even if it's marked as not for data output.
 248  *
 249  *              The encryption transform is permitted to corrupt @buf_u@ for
 250  *              its own purposes.  Neither the source nor destination should
 251  *              be within @buf_u@; and callers mustn't expect anything stored
 252  *              in @buf_u@ to still
 253  */
 254
 255 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
 256 {
 257   time_t now = time(0);
 258
 259   if (!KEYOK(ks, now)) {
 260     buf_break(bb);
 261     return (KSERR_NOKEYS);
 262   }
 263   return (doencrypt(ks, ty, b, bb));
 264 }
 265
 266 /* --- @ks_decrypt@ --- *
 267  *
 268  * Arguments:   @keyset *ks@ = pointer to a keyset
 269  *              @unsigned ty@ = expected type code
 270  *              @buf *b@ = pointer to an input buffer
 271  *              @buf *bb@ = pointer to an output buffer
 272  *
 273  * Returns:     Zero on success; @KSERR_...@ on failure.  Also returns
 274  *              zero if there was insufficient buffer (but the output buffer
 275  *              is broken in this case).
 276  *
 277  * Use:         Attempts to decrypt a message using a given key.  Note that
 278  *              requesting decryption with a key directly won't clear a
 279  *              marking that it's not for encryption.
 280  *
 281  *              The decryption transform is permitted to corrupt @buf_u@ for
 282  *              its own purposes.  Neither the source nor destination should
 283  *              be within @buf_u@; and callers mustn't expect anything stored
 284  *              in @buf_u@ to still
 285  */
 286
 287 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
 288 {
 289   time_t now = time(0);
 290   uint32 seq;
 291   int err;
 292
 293   if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
 294   if (buf_ensure(bb, BLEN(b))) return (0);
 295   if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
 296   if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
 297   return (0);
 298 }
 299
 300 /*----- Keyset list handling ----------------------------------------------*/
 301
 302 /* --- @ksl_free@ --- *
 303  *
 304  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 305  *
 306  * Returns:     ---
 307  *
 308  * Use:         Frees (releases references to) all of the keys in a keyset.
 309  */
 310
 311 void ksl_free(keyset **ksroot)
 312 {
 313   keyset *ks, *ksn;
 314   for (ks = *ksroot; ks; ks = ksn) {
 315     ksn = ks->next;
 316     ks->f &= ~KSF_LINK;
 317     ks_drop(ks);
 318   }
 319 }
 320
 321 /* --- @ksl_link@ --- *
 322  *
 323  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 324  *              @keyset *ks@ = pointer to a keyset
 325  *
 326  * Returns:     ---
 327  *
 328  * Use:         Links a keyset into a list.  A keyset can only be on one list
 329  *              at a time.  Bad things happen otherwise.
 330  */
 331
 332 void ksl_link(keyset **ksroot, keyset *ks)
 333 {
 334   assert(!(ks->f & KSF_LINK));
 335   ks->next = *ksroot;
 336   *ksroot = ks;
 337   ks->f |= KSF_LINK;
 338   ks->ref++;
 339 }
 340
 341 /* --- @ksl_prune@ --- *
 342  *
 343  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 344  *
 345  * Returns:     ---
 346  *
 347  * Use:         Prunes the keyset list by removing keys which mustn't be used
 348  *              any more.
 349  */
 350
 351 void ksl_prune(keyset **ksroot)
 352 {
 353   time_t now = time(0);
 354
 355   while (*ksroot) {
 356     keyset *ks = *ksroot;
 357
 358     if (ks->t_exp <= now) {
 359       T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
 360                ks->seq); )
 361       goto kill;
 362     } else if (ks->sz_exp == 0) {
 363       T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
 364                ks->seq); )
 365       goto kill;
 366     } else {
 367       ksroot = &ks->next;
 368       continue;
 369     }
 370
 371   kill:
 372     *ksroot = ks->next;
 373     ks->f &= ~KSF_LINK;
 374     ks_drop(ks);
 375   }
 376 }
 377
 378 /* --- @ksl_encrypt@ --- *
 379  *
 380  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 381  *              @unsigned ty@ = message type
 382  *              @buf *b@ = pointer to input buffer
 383  *              @buf *bb@ = pointer to output buffer
 384  *
 385  * Returns:     Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
 386  *              new key; @KSERR_NOKEYS@ if there are no suitable keys
 387  *              available.  Also returns zero if there was insufficient
 388  *              buffer space (but the output buffer is broken in this case).
 389  *
 390  * Use:         Encrypts a packet.
 391  */
 392
 393 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
 394 {
 395   time_t now = time(0);
 396   keyset *ks = *ksroot;
 397
 398   for (;;) {
 399     if (!ks) {
 400       T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
 401       buf_break(bb);
 402       return (KSERR_NOKEYS);
 403     }
 404     if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
 405       break;
 406     ks = ks->next;
 407   }
 408
 409   return (doencrypt(ks, ty, b, bb));
 410 }
 411
 412 /* --- @ksl_decrypt@ --- *
 413  *
 414  * Arguments:   @keyset **ksroot@ = pointer to keyset list head
 415  *              @unsigned ty@ = expected type code
 416  *              @buf *b@ = pointer to input buffer
 417  *              @buf *bb@ = pointer to output buffer
 418  *
 419  * Returns:     Zero on success; @KSERR_DECRYPT@ on failure.  Also returns
 420  *              zero if there was insufficient buffer (but the output buffer
 421  *              is broken in this case).
 422  *
 423  * Use:         Decrypts a packet.
 424  */
 425
 426 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
 427 {
 428   time_t now = time(0);
 429   keyset *ks;
 430   uint32 seq;
 431   int err;
 432
 433   if (buf_ensure(bb, BLEN(b)))
 434     return (0);
 435
 436   for (ks = *ksroot; ks; ks = ks->next) {
 437     if (!KEYOK(ks, now))
 438       continue;
 439     if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
 440       if (ks->f & KSF_LISTEN) {
 441         T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
 442                  ks->seq); )
 443         ks->f &= ~KSF_LISTEN;
 444       }
 445       if (seq_check(&ks->iseq, seq, "SYMM"))
 446         return (KSERR_SEQ);
 447       else
 448         return (0);
 449     }
 450     if (err != KSERR_DECRYPT) return (err);
 451   }
 452   T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
 453   return (KSERR_DECRYPT);
 454 }
 455
 456 /*----- That's all, folks -------------------------------------------------*/