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