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