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