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