src/DIPE.cxx

   1 #include "DIPE.h"
   2 #include "DIPE_Internal.h"
   3
   4 #include <string.h>
   5 #include <nettle/hkdf.h>
   6 #include <nettle/hmac.h>
   7 #include <sys/random.h>
   8 #include <nettle/gcm.h>
   9 #include <nettle/memops.h>
  10 #include <arpa/inet.h>
  11 #include <algorithm>
  12 #include <errno.h>
  13
  14 using std::min;
  15 using std::max;
  16
  17
  18
  19 namespace {
  20         size_t dipe_h_length(element_t elem, size_t dimension) {
  21                 return 16 /*cid*/ + dimension * element_length_in_bytes(elem);
  22         }
  23
  24         void dipe_generate_h(char* cid, element_t* y, size_t dimension, unsigned char* result) {
  25                 memcpy(result, cid, 16);
  26                 unsigned char* next_element = result+16;
  27                 for (size_t i = 0; i < dimension; ++i) {
  28                         element_to_bytes(next_element, y[i]);
  29                         next_element += element_length_in_bytes(y[0]);
  30                 }
  31         }
  32
  33         void dipe_generate_aeskey(element_t encapkey, uint8_t* aeskey) {
  34                 struct hmac_sha256_ctx ctx;
  35                 uint8_t salt[SHA256_DIGEST_SIZE];
  36                 memset(salt, 0, SHA256_DIGEST_SIZE);
  37                 size_t elen = element_length_in_bytes(encapkey);
  38                 uint8_t coded[elen];
  39                 element_to_bytes(coded, encapkey);
  40
  41                 hmac_sha256_set_key(&ctx, SHA256_DIGEST_SIZE, salt);
  42                 hkdf_extract(&ctx,
  43                                          (nettle_hash_update_func *)hmac_sha256_update,
  44                                          (nettle_hash_digest_func *)hmac_sha256_digest,
  45                                          SHA256_DIGEST_SIZE,
  46                                          elen, coded,
  47                                          aeskey);
  48         }
  49
  50         /* Data format is iv | enc(4 byte len | ptxt | 0 padding) | tag
  51          */
  52         int dipe_aes_encrypt(uint8_t* key, uint8_t* iv, size_t ptxt_len, uint8_t* ptxt, size_t ctxt_len, uint8_t* ctxt) {
  53                 struct gcm_aes128_ctx ctx;
  54                 uint8_t block[16];
  55                 uint32_t coded_ptxtlen;
  56
  57                 ctxt_len -= 16; /* Tag */
  58                 if (ctxt_len < ptxt_len + 4) return 0;
  59
  60                 memset(block, 0, 16);
  61                 gcm_aes128_set_key(&ctx, key);
  62                 gcm_aes128_set_iv(&ctx, 12, iv);
  63
  64                 /* First Block */
  65                 coded_ptxtlen = htonl(ptxt_len);
  66                 memcpy(block, &coded_ptxtlen, 4);
  67                 memcpy(block+4, ptxt, min((size_t)12, ptxt_len));
  68                 ptxt_len -= min((size_t)12, ptxt_len);
  69                 ptxt += 12;
  70
  71                 while (ctxt_len >= 16) {
  72                         gcm_aes128_encrypt(&ctx, 16, ctxt, block);
  73                         memset(block, 0, 16);
  74                         ctxt_len -= 16;
  75                         ctxt += 16;
  76
  77                         if (ptxt_len > 0) {
  78                                 memcpy(block, ptxt, min((size_t)16, ptxt_len));
  79                                 ptxt += 16;
  80                                 ptxt_len -= min((size_t)16, ptxt_len);
  81                         }
  82                 }
  83
  84                 if (ctxt_len > 0) {
  85                         gcm_aes128_encrypt(&ctx, ctxt_len, ctxt, block);
  86                         ctxt += ctxt_len;
  87                 }
  88
  89                 gcm_aes128_digest(&ctx, 16, ctxt);
  90                 return 0;
  91         }
  92
  93         int dipe_aes_decrypt(uint8_t* key, uint8_t* iv, size_t len, uint8_t* ctxt, uint8_t* ptxt) {
  94                 struct gcm_aes128_ctx ctx;
  95                 uint8_t block[16];
  96
  97                 gcm_aes128_set_key(&ctx, key);
  98                 gcm_aes128_set_iv(&ctx, 12, iv);
  99                 len -= 16; /* GCM tag */
 100
 101
 102                 gcm_aes128_decrypt(&ctx, min((size_t)16, len), block, ctxt);
 103                 uint32_t ptxtlen = 0;
 104                 memcpy(&ptxtlen, block, 4);
 105                 memcpy(ptxt, block+4, min((size_t)12, len-4));
 106                 ptxtlen = ntohl(ptxtlen);
 107                 ctxt += min((size_t)16, len); len -= min((size_t)16, len);
 108                 ptxt += 12;
 109
 110                 if (len > 0) {
 111                         gcm_aes128_decrypt(&ctx, len, ptxt, ctxt);
 112                         ctxt += len;
 113                 }
 114                 gcm_aes128_digest(&ctx, 16, block);
 115
 116                 /* error case is with return code 0, see manual
 117                  * https://www.lysator.liu.se/~nisse/nettle/nettle.html#Miscellaneous-functions
 118                  */
 119                 if (memeql_sec(ctxt, block, 16) == 0)
 120                         return 0;
 121                 else
 122                         return ptxtlen;
 123         }
 124 }
 125
 126 /* Note: we need a curve where membership checking is hard for all
 127  * group elements. See also https://ia.cr/2015/247 and followups
 128  */
 129 void dipe_init(FILE* configfp, dipe_param_t* param) {
 130         char buffer[2<<16];
 131         (*param) = (dipe_param_t)malloc(sizeof(dipe_param));
 132         fread(buffer, 1, 2<<16, configfp);
 133
 134         pairing_init_set_buf((*param)->pairing, buffer, 2<<16);
 135
 136         element_init_G1((*param)->g1, (*param)->pairing);
 137         element_init_G2((*param)->g2, (*param)->pairing);
 138         element_init_GT((*param)->gt, (*param)->pairing);
 139
 140         element_random((*param)->g1);
 141         element_random((*param)->g2);
 142         pairing_apply((*param)->gt, (*param)->g1, (*param)->g2, (*param)->pairing);
 143 }
 144
 145 pairing_t* dipe_get_pairing(dipe_param_t param) {
 146         return &(param->pairing);
 147 }
 148
 149 void dipe_master_keygen(dipe_param_t param, size_t dimension, dipe_master_publickey_t* pk, dipe_master_secretkey_t* sk) {
 150         *pk = (dipe_master_publickey_t)malloc(sizeof(dipe_master_publickey));
 151         *sk = (dipe_master_secretkey_t)malloc(sizeof(dipe_master_secretkey));
 152
 153         (*sk)->dimension = (*pk)->dimension = dimension;
 154
 155         element_init_Zr((*sk)->a, param->pairing);
 156         element_init_GT((*pk)->a, param->pairing);
 157         element_random((*sk)->a);
 158         element_pow_zn((*pk)->a, param->gt, (*sk)->a);
 159
 160         (*sk)->k = (element_t*)calloc(dimension, sizeof(element_t));
 161         (*pk)->k = (element_t*)calloc(dimension, sizeof(element_t));
 162         for (size_t i = 0; i < dimension; ++i) {
 163                 element_init_Zr((*sk)->k[i], param->pairing);
 164                 element_init_G1((*pk)->k[i], param->pairing);
 165                 element_random((*sk)->k[i]);
 166                 element_pow_zn((*pk)->k[i], param->g1, (*sk)->k[i]);
 167         }
 168 }
 169
 170 void dipe_keygen(dipe_param_t param, dipe_master_secretkey_t msk, char* cid, element_t* y, dipe_secretkey_t* sk) {
 171         *sk = (dipe_secretkey_t)malloc(sizeof(dipe_secretkey));
 172         (*sk)->dimension = msk->dimension;
 173         element_init_G2((*sk)->d, param->pairing);
 174
 175         size_t hash_input_length = dipe_h_length(y[0], msk->dimension);
 176         unsigned char hash_input[hash_input_length];
 177         element_t h;
 178         element_init_G2(h, param->pairing);
 179
 180         dipe_generate_h(cid, y, msk->dimension, hash_input);
 181         element_from_hash(h, hash_input, hash_input_length);
 182
 183         element_t innerp;
 184         element_t tmp;
 185
 186         element_init_Zr(innerp, param->pairing);
 187         element_init_Zr(tmp, param->pairing);
 188         element_set0(innerp);
 189
 190         element_from_hash(h, hash_input, hash_input_length);
 191
 192         for (size_t i = 0; i < msk->dimension; ++i) {
 193                 element_mul(tmp, y[i], msk->k[i]);
 194                 element_add(innerp, innerp, tmp);
 195         }
 196
 197         element_t a2;
 198         element_init_G2(a2, param->pairing);
 199         element_pow_zn(h, h, innerp);
 200         element_pow_zn(a2, param->g2, msk->a);
 201         element_mul((*sk)->d, a2, h);
 202
 203         element_clear(h);
 204         element_clear(innerp);
 205         element_clear(tmp);
 206         element_clear(a2);
 207 }
 208
 209 void dipe_encap(dipe_param_t param, dipe_master_publickey_t mpk, element_t* x, element_t ptxt, dipe_ctxt_t* ctxt) {
 210         *ctxt = (dipe_ctxt_t)malloc(sizeof(dipe_ctxt));
 211         (*ctxt)->dimension = mpk->dimension;
 212
 213         element_t r;
 214         element_t s;
 215         element_init_Zr(r, param->pairing);
 216         element_init_Zr(s, param->pairing);
 217
 218         element_random(r);
 219         element_random(s);
 220
 221         element_init_G1((*ctxt)->s, param->pairing);
 222         element_pow_zn((*ctxt)->s, param->g1, s);
 223
 224         element_t k1;
 225         element_t x1;
 226         element_init_G1(k1, param->pairing);
 227         element_init_G1(x1, param->pairing);
 228
 229         (*ctxt)->cx = (element_t*)calloc(mpk->dimension, sizeof(element_t));
 230         for (size_t i = 0; i < mpk->dimension; ++i){
 231                 element_pow_zn(x1, param->g1, x[i]);
 232                 element_pow_zn(x1, x1, r);
 233
 234                 element_pow_zn(k1, mpk->k[i], s);
 235
 236                 element_init_G1((*ctxt)->cx[i], param->pairing);
 237                 element_mul((*ctxt)->cx[i], k1, x1);
 238         }
 239
 240         element_t at;
 241         element_init_GT(at, param->pairing);
 242         element_pow_zn(at, mpk->a, s);
 243         element_init_GT((*ctxt)->c, param->pairing);
 244         element_mul((*ctxt)->c, at, ptxt);
 245
 246         element_clear(r);
 247         element_clear(s);
 248         element_clear(k1);
 249         element_clear(x1);
 250         element_clear(at);
 251 }
 252
 253
 254 void dipe_decap(dipe_param_t param, dipe_secretkey_t sk, char* cid, element_t* y, dipe_ctxt_t ctxt, element_t ptxt) {
 255         size_t hash_input_length = dipe_h_length(y[0], sk->dimension);
 256         unsigned char hash_input[hash_input_length];
 257         element_t h;
 258         element_init_G2(h, param->pairing);
 259
 260         dipe_generate_h(cid, y, sk->dimension, hash_input);
 261         element_from_hash(h, hash_input, hash_input_length);
 262
 263         element_t tmp;
 264         element_t innerp;
 265         element_t hy;
 266         element_init_GT(tmp, param->pairing);
 267         element_init_GT(innerp, param->pairing);
 268         element_init_G2(hy, param->pairing);
 269
 270         element_set1(innerp);
 271         for (size_t i = 0; i < sk->dimension; ++i) {
 272                 element_pow_zn(hy, h, y[i]);
 273                 pairing_apply(tmp, ctxt->cx[i], hy, param->pairing);
 274                 element_mul(innerp, innerp, tmp);
 275         }
 276
 277         pairing_apply(ptxt, ctxt->s, sk->d, param->pairing);
 278         element_invert(ptxt, ptxt);
 279         element_mul(ptxt, ptxt, ctxt->c);
 280         element_mul(ptxt, ptxt, innerp);
 281
 282         element_clear(h);
 283         element_clear(tmp);
 284         element_clear(innerp);
 285         element_clear(hy);
 286 }
 287
 288 void dipe_encrypt(dipe_param_t param, dipe_master_publickey_t mpk, element_t* x, size_t ptxt_len, char* ptxt, size_t ctxt_len, char* ctxt) {
 289         element_t key;
 290         uint8_t aes[32];
 291         dipe_ctxt_t cap;
 292         size_t cap_len;
 293
 294         element_init_GT(key, param->pairing);
 295         element_random(key);
 296         dipe_generate_aeskey(key, aes);
 297         dipe_encap(param, mpk, x, key, &cap);
 298         cap_len = dipe_serialize_ctxt(param, cap, (uint8_t*)ctxt);
 299         ctxt += cap_len; ctxt_len -= cap_len;
 300
 301         dipe_aes_encrypt(aes, aes+16, ptxt_len, (uint8_t*)ptxt, ctxt_len, (uint8_t*)ctxt);
 302
 303         dipe_free_ctxt(cap);
 304         element_clear(key);
 305 }
 306
 307 size_t dipe_decrypt(dipe_param_t param, dipe_secretkey_t sk, char* cid, element_t* y, size_t ctxt_len, char* ctxt, char* ptxt) {
 308         dipe_ctxt_t cap;
 309         uint8_t aes[32];
 310         element_t key;
 311         size_t cap_len;
 312
 313         element_init_GT(key, param->pairing);
 314         cap_len = dipe_deserialize_ctxt(param, sk->dimension, &cap, (uint8_t*)ctxt);
 315         ctxt += cap_len;
 316         ctxt_len -= cap_len;
 317         dipe_decap(param, sk, cid, y, cap, key);
 318         dipe_generate_aeskey(key, aes);
 319
 320         dipe_free_ctxt(cap);
 321         element_clear(key);
 322
 323         return dipe_aes_decrypt(aes, aes+16, ctxt_len, (uint8_t*)ctxt, (uint8_t*)ptxt);
 324 }
 325
 326 /* Note: we're generating random-looking bytes here. Therefore we
 327  * can't encode the dimension of the predicate vector (supposed to be
 328  * set as system parameter) or information about the secret sharing
 329  * (needs to be retrieved by some sort of trial decryption).
 330  */
 331 size_t dipe_serialize_ctxt(__attribute__((unused)) dipe_param_t param, dipe_ctxt_t ctxt, uint8_t* buffer) {
 332         size_t bytes_written = 0;
 333         element_to_bytes_compressed(buffer, ctxt->s);
 334         buffer += element_length_in_bytes_compressed(ctxt->s);
 335         bytes_written += element_length_in_bytes_compressed(ctxt->s);
 336
 337         for (size_t i = 0; i < ctxt->dimension; ++i) {
 338                 element_to_bytes_compressed(buffer, ctxt->cx[i]);
 339                 buffer += element_length_in_bytes_compressed(ctxt->cx[i]);
 340                 bytes_written += element_length_in_bytes_compressed(ctxt->cx[i]);
 341         }
 342
 343         element_to_bytes(buffer, ctxt->c);
 344         buffer += element_length_in_bytes(ctxt->c);
 345         bytes_written += element_length_in_bytes(ctxt->c);
 346
 347         return bytes_written;
 348 }
 349
 350 size_t dipe_deserialize_ctxt(dipe_param_t param, size_t dimension, dipe_ctxt_t* ctxt, uint8_t* buffer) {
 351         size_t bytes_read = 0;
 352         *ctxt = (dipe_ctxt_t)malloc(sizeof(dipe_ctxt));
 353         (*ctxt)->dimension = dimension;
 354
 355         element_init_G1((*ctxt)->s, param->pairing);
 356         element_from_bytes_compressed((*ctxt)->s, buffer);
 357         buffer += element_length_in_bytes_compressed((*ctxt)->s);
 358         bytes_read += element_length_in_bytes_compressed((*ctxt)->s);
 359
 360         (*ctxt)->cx = (element_t*)calloc(dimension, sizeof(element_t));
 361         for (size_t i = 0; i < dimension; ++i) {
 362                 element_init_G1((*ctxt)->cx[i], param->pairing);
 363                 element_from_bytes_compressed((*ctxt)->cx[i], buffer);
 364                 buffer += element_length_in_bytes_compressed((*ctxt)->cx[i]);
 365                 bytes_read += element_length_in_bytes_compressed((*ctxt)->cx[i]);
 366         }
 367
 368         element_init_GT((*ctxt)->c, param->pairing);
 369         element_from_bytes((*ctxt)->c, buffer);
 370         buffer += element_length_in_bytes((*ctxt)->c);
 371         bytes_read += element_length_in_bytes((*ctxt)->c);
 372
 373         return bytes_read;
 374 }
 375
 376 size_t dipe_ciphertext_overhead(dipe_param_t param, size_t dimension) {
 377         size_t overhead = 16 + 4 /* IV + Tag + Size */;
 378         element_t t;
 379
 380         element_init_G1(t, param->pairing);
 381         overhead += element_length_in_bytes_compressed(t);
 382         overhead += dimension * element_length_in_bytes_compressed(t);
 383         element_clear(t);
 384         element_init_GT(t, param->pairing);
 385         overhead += element_length_in_bytes(t);
 386         element_clear(t);
 387
 388         return overhead;
 389 }
 390
 391 void dipe_free_param(dipe_param_t param) {
 392         element_clear(param->g1);
 393         element_clear(param->g2);
 394         element_clear(param->gt);
 395         pairing_clear(param->pairing);
 396         free(param);
 397 }
 398
 399 void dipe_free_master_secretkey(dipe_master_secretkey_t sk) {
 400         for (size_t i = 0; i < sk->dimension; ++i) {
 401                 element_clear(sk->k[i]);
 402         }
 403         element_clear(sk->a);
 404         free(sk->k);
 405         free(sk);
 406 }
 407
 408 void dipe_free_master_publickey(dipe_master_publickey_t pk) {
 409         for (size_t i = 0; i < pk->dimension; ++i) {
 410                 element_clear(pk->k[i]);
 411         }
 412         element_clear(pk->a);
 413         free(pk->k);
 414         free(pk);
 415 }
 416
 417 void dipe_free_secretkey(dipe_secretkey_t sk) {
 418         element_clear(sk->d);
 419         free(sk);
 420 }
 421
 422 void dipe_free_ctxt(dipe_ctxt_t ctxt) {
 423         for (size_t i = 0; i < ctxt->dimension; ++i) {
 424                 element_clear(ctxt->cx[i]);
 425         }
 426         element_clear(ctxt->c);
 427         element_clear(ctxt->s);
 428         free(ctxt->cx);
 429         free(ctxt);
 430 }