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 #include "hexdebug.h"
  17
  18 /* Required key length in bytes */
  19 #define REQUIRED_KEYLEN ((512+64+32)/8)
  20
  21 struct transform {
  22     closure_t cl;
  23     struct transform_if ops;
  24     uint32_t max_seq_skew;
  25 };
  26
  27 struct transform_inst {
  28     struct transform_inst_if ops;
  29     struct keyInstance cryptkey;
  30     struct keyInstance mackey;
  31     uint32_t cryptiv;
  32     uint32_t maciv;
  33     uint32_t sendseq;
  34     uint32_t lastrecvseq;
  35     uint32_t max_skew;
  36     bool_t keyed;
  37 };
  38
  39 #define PKCS5_MASK 15
  40
  41 static bool_t transform_setkey(void *sst, uint8_t *key, int32_t keylen)
  42 {
  43     struct transform_inst *ti=sst;
  44
  45     if (keylen<REQUIRED_KEYLEN) {
  46         Message(M_ERR,"transform_create: insufficient key material supplied "
  47                 "(need %d bytes, got %d)\n",REQUIRED_KEYLEN,keylen);
  48         return False;
  49     }
  50
  51 #if 0
  52     {
  53         printf("Setting key to: ");
  54         hexdebug(stdout,key,keylen);
  55         printf("\n");
  56     }
  57 #endif /* 0 */
  58
  59     serpentbe_makekey(&ti->cryptkey,256,key);
  60     serpentbe_makekey(&ti->mackey,256,key+32);
  61     ti->cryptiv=get_uint32(key+64);
  62     ti->maciv=get_uint32(key+68);
  63     ti->sendseq=get_uint32(key+72);
  64     ti->lastrecvseq=ti->sendseq;
  65     ti->keyed=True;
  66
  67     return True;
  68 }
  69
  70 static bool_t transform_valid(void *sst)
  71 {
  72     struct transform_inst *ti=sst;
  73
  74     return ti->keyed;
  75 }
  76
  77 static void transform_delkey(void *sst)
  78 {
  79     struct transform_inst *ti=sst;
  80
  81     FILLZERO(ti->cryptkey);
  82     FILLZERO(ti->mackey);
  83     ti->keyed=False;
  84 }
  85
  86 static uint32_t transform_forward(void *sst, struct buffer_if *buf,
  87                                   const char **errmsg)
  88 {
  89     struct transform_inst *ti=sst;
  90     uint8_t *padp;
  91     int padlen;
  92     uint8_t iv[16];
  93     uint8_t macplain[16];
  94     uint8_t macacc[16];
  95     uint8_t *p, *n;
  96     int i;
  97
  98     if (!ti->keyed) {
  99         *errmsg="transform unkeyed";
 100         return 1;
 101     }
 102
 103     /* Sequence number */
 104     buf_prepend_uint32(buf,ti->sendseq);
 105     ti->sendseq++;
 106
 107     /* PKCS5, stolen from IWJ */
 108                                     /* eg with blocksize=4 mask=3 mask+2=5   */
 109                                     /* msgsize    20    21    22    23   24  */
 110     padlen= PKCS5_MASK-buf->size;   /*           -17   -18   -19   -16  -17  */
 111     padlen &= PKCS5_MASK;           /*             3     2     1     0    3  */
 112     padlen++;                       /*             4     3     2     1    4  */
 113
 114     padp=buf_append(buf,padlen);
 115     memset(padp,padlen,padlen);
 116
 117     /* Serpent-CBCMAC. We expand the IV from 32-bit to 128-bit using
 118        one encryption. Then we do the MAC and append the result. We don't
 119        bother sending the IV - it's the same each time. (If we wanted to send
 120        it we've have to add 16 bytes to each message, not 4, so that the
 121        message stays a multiple of 16 bytes long.) */
 122     memset(iv,0,16);
 123     put_uint32(iv, ti->maciv);
 124     serpentbe_encrypt(&ti->mackey,iv,macacc);
 125
 126     /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
 127        block encrypted once again. */
 128     for (n=buf->start; n<buf->start+buf->size; n+=16)
 129     {
 130         for (i = 0; i < 16; i++)
 131             macplain[i] = macacc[i] ^ n[i];
 132         serpentbe_encrypt(&ti->mackey,macplain,macacc);
 133     }
 134     serpentbe_encrypt(&ti->mackey,macacc,macacc);
 135     memcpy(buf_append(buf,16),macacc,16);
 136
 137     /* Serpent-CBC. We expand the ID as for CBCMAC, do the encryption,
 138        and prepend the IV before increasing it. */
 139     memset(iv,0,16);
 140     put_uint32(iv, ti->cryptiv);
 141     serpentbe_encrypt(&ti->cryptkey,iv,iv);
 142
 143     /* CBC: each block is XORed with the previous encrypted block (or the IV)
 144        before being encrypted. */
 145     p=iv;
 146
 147     for (n=buf->start; n<buf->start+buf->size; n+=16)
 148     {
 149         for (i = 0; i < 16; i++)
 150             n[i] ^= p[i];
 151         serpentbe_encrypt(&ti->cryptkey,n,n);
 152         p=n;
 153     }
 154
 155     buf_prepend_uint32(buf,ti->cryptiv);
 156     ti->cryptiv++;
 157     return 0;
 158 }
 159
 160 static uint32_t transform_reverse(void *sst, struct buffer_if *buf,
 161                                   const char **errmsg)
 162 {
 163     struct transform_inst *ti=sst;
 164     uint8_t *padp;
 165     int padlen;
 166     int i;
 167     uint32_t seqnum, skew;
 168     uint8_t iv[16];
 169     uint8_t pct[16];
 170     uint8_t macplain[16];
 171     uint8_t macacc[16];
 172     uint8_t *n;
 173     uint8_t *macexpected;
 174
 175     if (!ti->keyed) {
 176         *errmsg="transform unkeyed";
 177         return 1;
 178     }
 179
 180     if (buf->size < 4 + 16 + 16) {
 181         *errmsg="msg too short";
 182         return 1;
 183     }
 184
 185     /* CBC */
 186     memset(iv,0,16);
 187     {
 188         uint32_t ivword = buf_unprepend_uint32(buf);
 189         put_uint32(iv, ivword);
 190     }
 191     /* Assert bufsize is multiple of blocksize */
 192     if (buf->size&0xf) {
 193         *errmsg="msg not multiple of cipher blocksize";
 194         return 1;
 195     }
 196     serpentbe_encrypt(&ti->cryptkey,iv,iv);
 197     for (n=buf->start; n<buf->start+buf->size; n+=16)
 198     {
 199         for (i = 0; i < 16; i++)
 200             pct[i] = n[i];
 201         serpentbe_decrypt(&ti->cryptkey,n,n);
 202         for (i = 0; i < 16; i++)
 203             n[i] ^= iv[i];
 204         memcpy(iv, pct, 16);
 205     }
 206
 207     /* CBCMAC */
 208     macexpected=buf_unappend(buf,16);
 209     memset(iv,0,16);
 210     put_uint32(iv, ti->maciv);
 211     serpentbe_encrypt(&ti->mackey,iv,macacc);
 212
 213     /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
 214        block encrypted once again. */
 215     for (n=buf->start; n<buf->start+buf->size; n+=16)
 216     {
 217         for (i = 0; i < 16; i++)
 218             macplain[i] = macacc[i] ^ n[i];
 219         serpentbe_encrypt(&ti->mackey,macplain,macacc);
 220     }
 221     serpentbe_encrypt(&ti->mackey,macacc,macacc);
 222     if (!consttime_memeq(macexpected,macacc,16)!=0) {
 223         *errmsg="invalid MAC";
 224         return 1;
 225     }
 226
 227     /* PKCS5, stolen from IWJ */
 228
 229     padp=buf_unappend(buf,1);
 230     padlen=*padp;
 231     if (!padlen || (padlen > PKCS5_MASK+1)) {
 232         *errmsg="pkcs5: invalid length";
 233         return 1;
 234     }
 235
 236     buf_unappend(buf,padlen-1);
 237
 238     /* Sequence number must be within max_skew of lastrecvseq; lastrecvseq
 239        is only allowed to increase. */
 240     seqnum=buf_unprepend_uint32(buf);
 241     skew=seqnum-ti->lastrecvseq;
 242     if (skew<0x8fffffff) {
 243         /* Ok */
 244         ti->lastrecvseq=seqnum;
 245     } else if ((0-skew)<ti->max_skew) {
 246         /* Ok */
 247     } else {
 248         /* Too much skew */
 249         *errmsg="seqnum: too much skew";
 250         return 2;
 251     }
 252
 253     return 0;
 254 }
 255
 256 static void transform_destroy(void *sst)
 257 {
 258     struct transform_inst *st=sst;
 259
 260     FILLZERO(*st); /* Destroy key material */
 261     free(st);
 262 }
 263
 264 static struct transform_inst_if *transform_create(void *sst)
 265 {
 266     struct transform_inst *ti;
 267     struct transform *st=sst;
 268
 269     ti=safe_malloc(sizeof(*ti),"transform_create");
 270     /* mlock XXX */
 271
 272     ti->ops.st=ti;
 273     ti->ops.setkey=transform_setkey;
 274     ti->ops.valid=transform_valid;
 275     ti->ops.delkey=transform_delkey;
 276     ti->ops.forwards=transform_forward;
 277     ti->ops.reverse=transform_reverse;
 278     ti->ops.destroy=transform_destroy;
 279     ti->max_skew=st->max_seq_skew;
 280     ti->keyed=False;
 281
 282     return &ti->ops;
 283 }
 284
 285 static list_t *transform_apply(closure_t *self, struct cloc loc,
 286                                dict_t *context, list_t *args)
 287 {
 288     struct transform *st;
 289     item_t *item;
 290     dict_t *dict;
 291
 292     st=safe_malloc(sizeof(*st),"serpent");
 293     st->cl.description="serpent-cbc256";
 294     st->cl.type=CL_TRANSFORM;
 295     st->cl.apply=NULL;
 296     st->cl.interface=&st->ops;
 297     st->ops.st=st;
 298     st->ops.max_start_pad=28; /* 4byte seqnum, 16byte pad, 4byte MACIV,
 299                                  4byte IV */
 300     st->ops.max_end_pad=16; /* 16byte CBCMAC */
 301
 302     /* We need 256*2 bits for serpent keys, 32 bits for CBC-IV and 32 bits
 303        for CBCMAC-IV, and 32 bits for init sequence number */
 304     st->ops.keylen=REQUIRED_KEYLEN;
 305     st->ops.create=transform_create;
 306
 307     /* First parameter must be a dict */
 308     item=list_elem(args,0);
 309     if (!item || item->type!=t_dict)
 310         cfgfatal(loc,"userv-ipif","parameter must be a dictionary\n");
 311
 312     dict=item->data.dict;
 313     st->max_seq_skew=dict_read_number(dict, "max-sequence-skew",
 314                                       False, "serpent-cbc256", loc, 10);
 315
 316     return new_closure(&st->cl);
 317 }
 318
 319 void transform_module(dict_t *dict)
 320 {
 321     struct keyInstance k;
 322     uint8_t data[32];
 323     uint8_t plaintext[16];
 324     uint8_t ciphertext[16];
 325
 326     /*
 327      * Serpent self-test.
 328      *
 329      * This test pattern was taken directly from the Serpent test
 330      * vectors, which results in a big-endian Serpent which is not
 331      * compatible with other implementations.
 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     serpentbe_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     serpentbe_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     serpentbe_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 }