mdw@git.distorted.org.uk Git - secnet/blob - transform-cbcmac.c

   1 /* Transform module - bulk data transformation */
   2
   3 /*
   4  * This file is part of secnet.
   5  * See README for full list of copyright holders.
   6  *
   7  * secnet is free software; you can redistribute it and/or modify it
   8  * under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 3 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * secnet is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * version 3 along with secnet; if not, see
  19  * https://www.gnu.org/licenses/gpl.html.
  20  */
  21
  22 /* For now it's hard-coded to do sequence
  23    number/pkcs5/serpent-cbcmac/serpent with a 256 bit key for each
  24    instance of serpent. We also require key material for the IVs for
  25    cbcmac and cbc. Hack: we're not using full 128-bit IVs, we're just
  26    using 32 bits and encrypting to get the full IV to save space in
  27    the packets sent over the wire. */
  28
  29 #include <stdio.h>
  30 #include <string.h>
  31 #include "secnet.h"
  32 #include "util.h"
  33 #include "serpent.h"
  34 #include "unaligned.h"
  35 #include "hexdebug.h"
  36
  37 /* Required key length in bytes */
  38 #define REQUIRED_KEYLEN ((512+64+32)/8)
  39
  40 #include "transform-common.h"
  41
  42 struct transform_params {
  43     SEQNUM_PARAMS_FIELDS;
  44 };
  45
  46 struct transform {
  47     closure_t cl;
  48     struct transform_if ops;
  49     struct transform_params p;
  50 };
  51
  52 struct transform_inst {
  53     struct transform_inst_if ops;
  54     struct transform_params p;
  55     struct keyInstance cryptkey;
  56     struct keyInstance mackey;
  57     uint32_t cryptiv;
  58     uint32_t maciv;
  59     SEQNUM_KEYED_FIELDS;
  60 };
  61
  62 #define PKCS5_MASK 15
  63
  64 static bool_t transform_setkey(void *sst, uint8_t *key, int32_t keylen,
  65                                bool_t direction)
  66 {
  67     struct transform_inst *ti=sst;
  68
  69     if (keylen<REQUIRED_KEYLEN) {
  70         Message(M_ERR,"transform_create: insufficient key material supplied "
  71                 "(need %d bytes, got %d)\n",REQUIRED_KEYLEN,keylen);
  72         return False;
  73     }
  74
  75 #if 0
  76     {
  77         printf("Setting key to: ");
  78         hexdebug(stdout,key,keylen);
  79         printf("\n");
  80     }
  81 #endif /* 0 */
  82
  83     serpentbe_makekey(&ti->cryptkey,256,key);
  84     serpentbe_makekey(&ti->mackey,256,key+32);
  85     ti->cryptiv=get_uint32(key+64);
  86     ti->maciv=get_uint32(key+68);
  87     uint32_t firstseq=get_uint32(key+72);
  88     SEQNUM_KEYED_INIT(firstseq,firstseq);
  89
  90     return True;
  91 }
  92
  93 TRANSFORM_VALID;
  94
  95 static void transform_delkey(void *sst)
  96 {
  97     struct transform_inst *ti=sst;
  98
  99     FILLZERO(ti->cryptkey);
 100     FILLZERO(ti->mackey);
 101     ti->keyed=False;
 102 }
 103
 104 static transform_apply_return transform_forward(void *sst,
 105             struct buffer_if *buf, const char **errmsg)
 106 {
 107     struct transform_inst *ti=sst;
 108     uint8_t *padp;
 109     int padlen;
 110     uint8_t iv[16];
 111     uint8_t macplain[16];
 112     uint8_t macacc[16];
 113     uint8_t *p, *n;
 114     int i;
 115
 116     KEYED_CHECK;
 117
 118     /* Sequence number */
 119     buf_prepend_uint32(buf,ti->sendseq);
 120     ti->sendseq++;
 121
 122     /* PKCS5, stolen from IWJ */
 123                                     /* eg with blocksize=4 mask=3 mask+2=5   */
 124                                     /* msgsize    20    21    22    23   24  */
 125     padlen= PKCS5_MASK-buf->size;   /*           -17   -18   -19   -16  -17  */
 126     padlen &= PKCS5_MASK;           /*             3     2     1     0    3  */
 127     padlen++;                       /*             4     3     2     1    4  */
 128
 129     padp=buf_append(buf,padlen);
 130     memset(padp,padlen,padlen);
 131
 132     /* Serpent-CBCMAC. We expand the IV from 32-bit to 128-bit using
 133        one encryption. Then we do the MAC and append the result. We don't
 134        bother sending the IV - it's the same each time. (If we wanted to send
 135        it we've have to add 16 bytes to each message, not 4, so that the
 136        message stays a multiple of 16 bytes long.) */
 137     FILLZERO(iv);
 138     put_uint32(iv, ti->maciv);
 139     serpentbe_encrypt(&ti->mackey,iv,macacc);
 140
 141     /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
 142        block encrypted once again. */
 143     for (n=buf->start; n<buf->start+buf->size; n+=16)
 144     {
 145         for (i = 0; i < 16; i++)
 146             macplain[i] = macacc[i] ^ n[i];
 147         serpentbe_encrypt(&ti->mackey,macplain,macacc);
 148     }
 149     serpentbe_encrypt(&ti->mackey,macacc,macacc);
 150     BUF_ADD_BYTES(append,buf,macacc,16);
 151
 152     /* Serpent-CBC. We expand the ID as for CBCMAC, do the encryption,
 153        and prepend the IV before increasing it. */
 154     FILLZERO(iv);
 155     put_uint32(iv, ti->cryptiv);
 156     serpentbe_encrypt(&ti->cryptkey,iv,iv);
 157
 158     /* CBC: each block is XORed with the previous encrypted block (or the IV)
 159        before being encrypted. */
 160     p=iv;
 161
 162     for (n=buf->start; n<buf->start+buf->size; n+=16)
 163     {
 164         for (i = 0; i < 16; i++)
 165             n[i] ^= p[i];
 166         serpentbe_encrypt(&ti->cryptkey,n,n);
 167         p=n;
 168     }
 169
 170     buf_prepend_uint32(buf,ti->cryptiv);
 171     ti->cryptiv++;
 172     return 0;
 173 }
 174
 175 static transform_apply_return transform_reverse(void *sst,
 176                 struct buffer_if *buf, const char **errmsg)
 177 {
 178     struct transform_inst *ti=sst;
 179     uint8_t *padp;
 180     int padlen;
 181     int i;
 182     uint32_t seqnum;
 183     uint8_t iv[16];
 184     uint8_t pct[16];
 185     uint8_t macplain[16];
 186     uint8_t macacc[16];
 187     uint8_t *n;
 188     uint8_t *macexpected;
 189
 190     KEYED_CHECK;
 191
 192     if (buf->size < 4 + 16 + 16) {
 193         *errmsg="msg too short";
 194         return transform_apply_err;
 195     }
 196
 197     /* CBC */
 198     FILLZERO(iv);
 199     {
 200         uint32_t ivword = buf_unprepend_uint32(buf);
 201         put_uint32(iv, ivword);
 202     }
 203     /* Assert bufsize is multiple of blocksize */
 204     if (buf->size&0xf) {
 205         *errmsg="msg not multiple of cipher blocksize";
 206         return transform_apply_err;
 207     }
 208     serpentbe_encrypt(&ti->cryptkey,iv,iv);
 209     for (n=buf->start; n<buf->start+buf->size; n+=16)
 210     {
 211         for (i = 0; i < 16; i++)
 212             pct[i] = n[i];
 213         serpentbe_decrypt(&ti->cryptkey,n,n);
 214         for (i = 0; i < 16; i++)
 215             n[i] ^= iv[i];
 216         COPY_OBJ(iv, pct);
 217     }
 218
 219     /* CBCMAC */
 220     macexpected=buf_unappend(buf,16);
 221     FILLZERO(iv);
 222     put_uint32(iv, ti->maciv);
 223     serpentbe_encrypt(&ti->mackey,iv,macacc);
 224
 225     /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
 226        block encrypted once again. */
 227     for (n=buf->start; n<buf->start+buf->size; n+=16)
 228     {
 229         for (i = 0; i < 16; i++)
 230             macplain[i] = macacc[i] ^ n[i];
 231         serpentbe_encrypt(&ti->mackey,macplain,macacc);
 232     }
 233     serpentbe_encrypt(&ti->mackey,macacc,macacc);
 234     if (!consttime_memeq(macexpected,macacc,16)) {
 235         *errmsg="invalid MAC";
 236         return transform_apply_err;
 237     }
 238
 239     /* PKCS5, stolen from IWJ */
 240
 241     padp=buf_unappend(buf,1);
 242     padlen=*padp;
 243     if (!padlen || (padlen > PKCS5_MASK+1)) {
 244         *errmsg="pkcs5: invalid length";
 245         return transform_apply_err;
 246     }
 247
 248     buf_unappend(buf,padlen-1);
 249
 250     /* Sequence number must be within max_skew of lastrecvseq; lastrecvseq
 251        is only allowed to increase. */
 252     seqnum=buf_unprepend_uint32(buf);
 253     SEQNUM_CHECK(seqnum, &ti->p);
 254
 255     return 0;
 256 }
 257
 258 TRANSFORM_DESTROY;
 259
 260 static struct transform_inst_if *transform_create(void *sst)
 261 {
 262     struct transform *st=sst;
 263
 264     TRANSFORM_CREATE_CORE;
 265
 266     ti->p=st->p;
 267
 268     return &ti->ops;
 269 }
 270
 271 static list_t *transform_apply(closure_t *self, struct cloc loc,
 272                                dict_t *context, list_t *args)
 273 {
 274     struct transform *st;
 275     item_t *item;
 276     dict_t *dict;
 277
 278     NEW(st);
 279     st->cl.description="serpent-cbc256";
 280     st->cl.type=CL_TRANSFORM;
 281     st->cl.apply=NULL;
 282     st->cl.interface=&st->ops;
 283     st->ops.st=st;
 284     update_max_start_pad(&transform_max_start_pad, 28);
 285         /* 4byte seqnum, 16byte pad, 4byte MACIV, 4byte IV */
 286
 287     /* We need 256*2 bits for serpent keys, 32 bits for CBC-IV and 32 bits
 288        for CBCMAC-IV, and 32 bits for init sequence number */
 289     st->ops.keylen=REQUIRED_KEYLEN;
 290     st->ops.create=transform_create;
 291
 292     /* First parameter must be a dict */
 293     item=list_elem(args,0);
 294     if (!item || item->type!=t_dict)
 295         cfgfatal(loc,"serpent256-cbc","parameter must be a dictionary\n");
 296
 297     dict=item->data.dict;
 298
 299     SEQNUM_PARAMS_INIT(dict,&st->p,"serpent-cbc256",loc);
 300
 301     SET_CAPAB_TRANSFORMNUM(CAPAB_TRANSFORMNUM_SERPENT256CBC);
 302
 303     return new_closure(&st->cl);
 304 }
 305
 306 void transform_cbcmac_module(dict_t *dict)
 307 {
 308     struct keyInstance k;
 309     uint8_t data[32];
 310     uint8_t plaintext[16];
 311     uint8_t ciphertext[16];
 312
 313     /*
 314      * Serpent self-test.
 315      *
 316      * This test pattern was taken directly from the Serpent test
 317      * vectors, which results in a big-endian Serpent which is not
 318      * compatible with other implementations.
 319      */
 320
 321     /* Serpent self-test */
 322     memcpy(data,
 323            "\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb\xcc\xdd\xee\xff"
 324            "\xff\xee\xdd\xcc\xbb\xaa\x99\x88\x77\x66\x55\x44\x33\x22\x11\x00",
 325            32);
 326     serpentbe_makekey(&k,256,data);
 327
 328     memcpy(plaintext,
 329            "\x01\x23\x45\x67\x89\xab\xcd\xef\xfe\xdc\xba\x98\x76\x54\x32\x10",
 330            16);
 331     serpentbe_encrypt(&k,plaintext,ciphertext);
 332
 333     if (memcmp(ciphertext, "\xca\x7f\xa1\x93\xe3\xeb\x9e\x99"
 334                "\xbd\x87\xe3\xaf\x3c\x9a\xdf\x93", 16)) {
 335         fatal("transform_module: serpent failed self-test (encrypt)");
 336     }
 337     serpentbe_decrypt(&k,ciphertext,plaintext);
 338     if (memcmp(plaintext, "\x01\x23\x45\x67\x89\xab\xcd\xef"
 339                "\xfe\xdc\xba\x98\x76\x54\x32\x10", 16)) {
 340         fatal("transform_module: serpent failed self-test (decrypt)");
 341     }
 342
 343     add_closure(dict,"serpent256-cbc",transform_apply);
 344
 345 #ifdef TEST_WHOLE_TRANSFORM
 346     {
 347         struct transform *tr;
 348         void *ti;
 349         struct buffer_if buf;
 350         const char text[] = "This is a piece of test text.";
 351         char keymaterial[76] =
 352             "Seventy-six bytes i"
 353             "n four rows of 19; "
 354             "this looks almost l"
 355             "ike a poem but not.";
 356         const char *errmsg;
 357         int i;
 358
 359         NEW(tr);
 360         tr->max_seq_skew = 20;
 361         ti = transform_create(tr);
 362
 363         transform_setkey(ti, keymaterial, 76);
 364
 365         buf.base = malloc(4096);
 366         buffer_init(&buf, 2048);
 367         BUF_ADD_OBJ(append, buf, text, sizeof(text));
 368         if (transform_forward(ti, &buf, &errmsg)) {
 369             fatal("transform_forward test: %s", errmsg);
 370         }
 371         printf("transformed text is:\n");
 372         for (i = 0; i < buf.size; i++)
 373             printf("%02x%c", buf.start[i],
 374                    (i%16==15 || i==buf.size-1 ? '\n' : ' '));
 375         if (transform_reverse(ti, &buf, &errmsg)) {
 376             fatal("transform_reverse test: %s", errmsg);
 377         }
 378         printf("transform reversal worked OK\n");
 379     }
 380 #endif
 381 }