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

   1 /* Transform module - bulk data transformation */
   2
   3 /* For now it's hard-coded to do sequence
   4    number/pkcs5/serpent-cbcmac/serpent with a 256 bit key for each
   5    instance of serpent. We also require key material for the IVs for
   6    cbcmac and cbc. Hack: we're not using full 128-bit IVs, we're just
   7    using 32 bits and encrypting to get the full IV to save space in
   8    the packets sent over the wire. */
   9
  10 #include <stdio.h>
  11 #include <string.h>
  12 #include "secnet.h"
  13 #include "util.h"
  14 #include "serpent.h"
  15 #include "unaligned.h"
  16
  17 /* Required key length in bytes */
  18 #define REQUIRED_KEYLEN ((512+64+32)/8)
  19
  20 struct transform {
  21     closure_t cl;
  22     struct transform_if ops;
  23     uint32_t max_seq_skew;
  24 };
  25
  26 struct transform_inst {
  27     struct transform_inst_if ops;
  28     struct keyInstance cryptkey;
  29     struct keyInstance mackey;
  30     uint32_t cryptiv;
  31     uint32_t maciv;
  32     uint32_t sendseq;
  33     uint32_t lastrecvseq;
  34     uint32_t max_skew;
  35     bool_t keyed;
  36 };
  37
  38 #define PKCS5_MASK 15
  39
  40 static bool_t transform_setkey(void *sst, uint8_t *key, int32_t keylen)
  41 {
  42     struct transform_inst *ti=sst;
  43
  44     if (keylen<REQUIRED_KEYLEN) {
  45         Message(M_ERR,"transform_create: insufficient key material supplied "
  46                 "(need %d bytes, got %d)\n",REQUIRED_KEYLEN,keylen);
  47         return False;
  48     }
  49
  50 #if 0
  51     {
  52         int i;
  53         printf("Setting key to: ");
  54         for (i=0; i<keylen; i++)
  55             printf("%02x",key[i]);
  56         printf("\n");
  57     }
  58 #endif /* 0 */
  59
  60     serpent_makekey(&ti->cryptkey,256,key);
  61     serpent_makekey(&ti->mackey,256,key+32);
  62     ti->cryptiv=get_uint32(key+64);
  63     ti->maciv=get_uint32(key+68);
  64     ti->sendseq=get_uint32(key+72);
  65     ti->lastrecvseq=ti->sendseq;
  66     ti->keyed=True;
  67
  68     return True;
  69 }
  70
  71 static bool_t transform_valid(void *sst)
  72 {
  73     struct transform_inst *ti=sst;
  74
  75     return ti->keyed;
  76 }
  77
  78 static void transform_delkey(void *sst)
  79 {
  80     struct transform_inst *ti=sst;
  81
  82     FILLZERO(ti->cryptkey);
  83     FILLZERO(ti->mackey);
  84     ti->keyed=False;
  85 }
  86
  87 static uint32_t transform_forward(void *sst, struct buffer_if *buf,
  88                                   const char **errmsg)
  89 {
  90     struct transform_inst *ti=sst;
  91     uint8_t *padp;
  92     int padlen;
  93     uint8_t iv[16];
  94     uint8_t macplain[16];
  95     uint8_t macacc[16];
  96     uint8_t *p, *n;
  97     int i;
  98
  99     if (!ti->keyed) {
 100         *errmsg="transform unkeyed";
 101         return 1;
 102     }
 103
 104     /* Sequence number */
 105     buf_prepend_uint32(buf,ti->sendseq);
 106     ti->sendseq++;
 107
 108     /* PKCS5, stolen from IWJ */
 109                                     /* eg with blocksize=4 mask=3 mask+2=5   */
 110                                     /* msgsize    20    21    22    23   24  */
 111     padlen= PKCS5_MASK-buf->size;   /*           -17   -18   -19   -16  -17  */
 112     padlen &= PKCS5_MASK;           /*             3     2     1     0    3  */
 113     padlen++;                       /*             4     3     2     1    4  */
 114
 115     padp=buf_append(buf,padlen);
 116     memset(padp,padlen,padlen);
 117
 118     /* Serpent-CBCMAC. We expand the IV from 32-bit to 128-bit using
 119        one encryption. Then we do the MAC and append the result. We don't
 120        bother sending the IV - it's the same each time. (If we wanted to send
 121        it we've have to add 16 bytes to each message, not 4, so that the
 122        message stays a multiple of 16 bytes long.) */
 123     memset(iv,0,16);
 124     put_uint32(iv, ti->maciv);
 125     serpent_encrypt(&ti->mackey,iv,macacc);
 126
 127     /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
 128        block encrypted once again. */
 129     for (n=buf->start; n<buf->start+buf->size; n+=16)
 130     {
 131         for (i = 0; i < 16; i++)
 132             macplain[i] = macacc[i] ^ n[i];
 133         serpent_encrypt(&ti->mackey,macplain,macacc);
 134     }
 135     serpent_encrypt(&ti->mackey,macacc,macacc);
 136     memcpy(buf_append(buf,16),macacc,16);
 137
 138     /* Serpent-CBC. We expand the ID as for CBCMAC, do the encryption,
 139        and prepend the IV before increasing it. */
 140     memset(iv,0,16);
 141     put_uint32(iv, ti->cryptiv);
 142     serpent_encrypt(&ti->cryptkey,iv,iv);
 143
 144     /* CBC: each block is XORed with the previous encrypted block (or the IV)
 145        before being encrypted. */
 146     p=iv;
 147
 148     for (n=buf->start; n<buf->start+buf->size; n+=16)
 149     {
 150         for (i = 0; i < 16; i++)
 151             n[i] ^= p[i];
 152         serpent_encrypt(&ti->cryptkey,n,n);
 153         p=n;
 154     }
 155
 156     buf_prepend_uint32(buf,ti->cryptiv);
 157     ti->cryptiv++;
 158     return 0;
 159 }
 160
 161 static uint32_t transform_reverse(void *sst, struct buffer_if *buf,
 162                                   const char **errmsg)
 163 {
 164     struct transform_inst *ti=sst;
 165     uint8_t *padp;
 166     int padlen;
 167     int i;
 168     uint32_t seqnum, skew;
 169     uint8_t iv[16];
 170     uint8_t pct[16];
 171     uint8_t macplain[16];
 172     uint8_t macacc[16];
 173     uint8_t *n;
 174     uint8_t *macexpected;
 175
 176     if (!ti->keyed) {
 177         *errmsg="transform unkeyed";
 178         return 1;
 179     }
 180
 181     if (buf->size < 4 + 16 + 16) {
 182         *errmsg="msg too short";
 183         return 1;
 184     }
 185
 186     /* CBC */
 187     memset(iv,0,16);
 188     {
 189         uint32_t ivword = buf_unprepend_uint32(buf);
 190         put_uint32(iv, ivword);
 191     }
 192     /* Assert bufsize is multiple of blocksize */
 193     if (buf->size&0xf) {
 194         *errmsg="msg not multiple of cipher blocksize";
 195         return 1;
 196     }
 197     serpent_encrypt(&ti->cryptkey,iv,iv);
 198     for (n=buf->start; n<buf->start+buf->size; n+=16)
 199     {
 200         for (i = 0; i < 16; i++)
 201             pct[i] = n[i];
 202         serpent_decrypt(&ti->cryptkey,n,n);
 203         for (i = 0; i < 16; i++)
 204             n[i] ^= iv[i];
 205         memcpy(iv, pct, 16);
 206     }
 207
 208     /* CBCMAC */
 209     macexpected=buf_unappend(buf,16);
 210     memset(iv,0,16);
 211     put_uint32(iv, ti->maciv);
 212     serpent_encrypt(&ti->mackey,iv,macacc);
 213
 214     /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
 215        block encrypted once again. */
 216     for (n=buf->start; n<buf->start+buf->size; n+=16)
 217     {
 218         for (i = 0; i < 16; i++)
 219             macplain[i] = macacc[i] ^ n[i];
 220         serpent_encrypt(&ti->mackey,macplain,macacc);
 221     }
 222     serpent_encrypt(&ti->mackey,macacc,macacc);
 223     if (!consttime_memeq(macexpected,macacc,16)!=0) {
 224         *errmsg="invalid MAC";
 225         return 1;
 226     }
 227
 228     /* PKCS5, stolen from IWJ */
 229
 230     padp=buf_unappend(buf,1);
 231     padlen=*padp;
 232     if (!padlen || (padlen > PKCS5_MASK+1)) {
 233         *errmsg="pkcs5: invalid length";
 234         return 1;
 235     }
 236
 237     buf_unappend(buf,padlen-1);
 238
 239     /* Sequence number must be within max_skew of lastrecvseq; lastrecvseq
 240        is only allowed to increase. */
 241     seqnum=buf_unprepend_uint32(buf);
 242     skew=seqnum-ti->lastrecvseq;
 243     if (skew<0x8fffffff) {
 244         /* Ok */
 245         ti->lastrecvseq=seqnum;
 246     } else if ((0-skew)<ti->max_skew) {
 247         /* Ok */
 248     } else {
 249         /* Too much skew */
 250         *errmsg="seqnum: too much skew";
 251         return 2;
 252     }
 253
 254     return 0;
 255 }
 256
 257 static void transform_destroy(void *sst)
 258 {
 259     struct transform_inst *st=sst;
 260
 261     FILLZERO(*st); /* Destroy key material */
 262     free(st);
 263 }
 264
 265 static struct transform_inst_if *transform_create(void *sst)
 266 {
 267     struct transform_inst *ti;
 268     struct transform *st=sst;
 269
 270     ti=safe_malloc(sizeof(*ti),"transform_create");
 271     /* mlock XXX */
 272
 273     ti->ops.st=ti;
 274     ti->ops.setkey=transform_setkey;
 275     ti->ops.valid=transform_valid;
 276     ti->ops.delkey=transform_delkey;
 277     ti->ops.forwards=transform_forward;
 278     ti->ops.reverse=transform_reverse;
 279     ti->ops.destroy=transform_destroy;
 280     ti->max_skew=st->max_seq_skew;
 281     ti->keyed=False;
 282
 283     return &ti->ops;
 284 }
 285
 286 static list_t *transform_apply(closure_t *self, struct cloc loc,
 287                                dict_t *context, list_t *args)
 288 {
 289     struct transform *st;
 290     item_t *item;
 291     dict_t *dict;
 292
 293     st=safe_malloc(sizeof(*st),"serpent");
 294     st->cl.description="serpent-cbc256";
 295     st->cl.type=CL_TRANSFORM;
 296     st->cl.apply=NULL;
 297     st->cl.interface=&st->ops;
 298     st->ops.st=st;
 299     st->ops.max_start_pad=28; /* 4byte seqnum, 16byte pad, 4byte MACIV,
 300                                  4byte IV */
 301     st->ops.max_end_pad=16; /* 16byte CBCMAC */
 302
 303     /* We need 256*2 bits for serpent keys, 32 bits for CBC-IV and 32 bits
 304        for CBCMAC-IV, and 32 bits for init sequence number */
 305     st->ops.keylen=REQUIRED_KEYLEN;
 306     st->ops.create=transform_create;
 307
 308     /* First parameter must be a dict */
 309     item=list_elem(args,0);
 310     if (!item || item->type!=t_dict)
 311         cfgfatal(loc,"userv-ipif","parameter must be a dictionary\n");
 312
 313     dict=item->data.dict;
 314     st->max_seq_skew=dict_read_number(dict, "max-sequence-skew",
 315                                       False, "serpent-cbc256", loc, 10);
 316
 317     return new_closure(&st->cl);
 318 }
 319
 320 void transform_module(dict_t *dict)
 321 {
 322     struct keyInstance k;
 323     uint8_t data[32];
 324     uint8_t plaintext[16];
 325     uint8_t ciphertext[16];
 326
 327     /*
 328      * Serpent self-test.
 329      *
 330      * This test pattern is taken directly from the Serpent test
 331      * vectors, to ensure we have all endianness issues correct. -sgt
 332      */
 333
 334     /* Serpent self-test */
 335     memcpy(data,
 336            "\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb\xcc\xdd\xee\xff"
 337            "\xff\xee\xdd\xcc\xbb\xaa\x99\x88\x77\x66\x55\x44\x33\x22\x11\x00",
 338            32);
 339     serpent_makekey(&k,256,data);
 340
 341     memcpy(plaintext,
 342            "\x01\x23\x45\x67\x89\xab\xcd\xef\xfe\xdc\xba\x98\x76\x54\x32\x10",
 343            16);
 344     serpent_encrypt(&k,plaintext,ciphertext);
 345
 346     if (memcmp(ciphertext, "\xca\x7f\xa1\x93\xe3\xeb\x9e\x99"
 347                "\xbd\x87\xe3\xaf\x3c\x9a\xdf\x93", 16)) {
 348         fatal("transform_module: serpent failed self-test (encrypt)");
 349     }
 350     serpent_decrypt(&k,ciphertext,plaintext);
 351     if (memcmp(plaintext, "\x01\x23\x45\x67\x89\xab\xcd\xef"
 352                "\xfe\xdc\xba\x98\x76\x54\x32\x10", 16)) {
 353         fatal("transform_module: serpent failed self-test (decrypt)");
 354     }
 355
 356     add_closure(dict,"serpent256-cbc",transform_apply);
 357
 358 #ifdef TEST_WHOLE_TRANSFORM
 359     {
 360         struct transform *tr;
 361         void *ti;
 362         struct buffer_if buf;
 363         const char text[] = "This is a piece of test text.";
 364         char keymaterial[76] =
 365             "Seventy-six bytes i"
 366             "n four rows of 19; "
 367             "this looks almost l"
 368             "ike a poem but not.";
 369         const char *errmsg;
 370         int i;
 371
 372         tr = malloc(sizeof(struct transform));
 373         tr->max_seq_skew = 20;
 374         ti = transform_create(tr);
 375
 376         transform_setkey(ti, keymaterial, 76);
 377
 378         buf.base = malloc(4096);
 379         buffer_init(&buf, 2048);
 380         memcpy(buf_append(&buf, sizeof(text)), text, sizeof(text));
 381         if (transform_forward(ti, &buf, &errmsg)) {
 382             fatal("transform_forward test: %s", errmsg);
 383         }
 384         printf("transformed text is:\n");
 385         for (i = 0; i < buf.size; i++)
 386             printf("%02x%c", buf.start[i],
 387                    (i%16==15 || i==buf.size-1 ? '\n' : ' '));
 388         if (transform_reverse(ti, &buf, &errmsg)) {
 389             fatal("transform_reverse test: %s", errmsg);
 390         }
 391         printf("transform reversal worked OK\n");
 392     }
 393 #endif
 394 }