| 1 | /* |
| 2 | * eax-transform.c: EAX-Serpent bulk data transformation |
| 3 | */ |
| 4 | /* |
| 5 | * This file is part of secnet. |
| 6 | * See README for full list of copyright holders. |
| 7 | * |
| 8 | * secnet is free software; you can redistribute it and/or modify it |
| 9 | * under the terms of the GNU General Public License as published by |
| 10 | * the Free Software Foundation; either version 3 of the License, or |
| 11 | * (at your option) any later version. |
| 12 | * |
| 13 | * secnet is distributed in the hope that it will be useful, but |
| 14 | * WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 16 | * General Public License for more details. |
| 17 | * |
| 18 | * You should have received a copy of the GNU General Public License |
| 19 | * version 3 along with secnet; if not, see |
| 20 | * https://www.gnu.org/licenses/gpl.html. |
| 21 | */ |
| 22 | /* |
| 23 | * We use EAX with the following parameters: |
| 24 | * |
| 25 | * Plaintext: |
| 26 | * Concatenation of: |
| 27 | * Data packet as supplied to us |
| 28 | * Zero or more zero bytes ignored by receiver } padding |
| 29 | * One byte padding length } |
| 30 | * This is a bit like PKCS#5. It helps disguise message lengths. |
| 31 | * It also provides a further room for future expansion. When |
| 32 | * transmitting we pad the message to the next multiple of |
| 33 | * a configurable rounding factor, 16 bytes by default. |
| 34 | * |
| 35 | * Transmitted message: |
| 36 | * Concatenation of: |
| 37 | * EAX ciphertext |
| 38 | * 32-bit sequence number (initially zero) |
| 39 | * The sequence number allows us to discard far-too-old |
| 40 | * packets. |
| 41 | * |
| 42 | * Nonce: |
| 43 | * Concatenation of: |
| 44 | * 32-bit sequence number (big endian) |
| 45 | * initial value comes from SHA-512 hash (see below) |
| 46 | * 1 byte: 0x01 if sender has setup priority, 0x00 if it doesn't |
| 47 | * (ie, the direction of data flow) |
| 48 | * |
| 49 | * Header: None |
| 50 | * |
| 51 | * Tag length: |
| 52 | * 16 bytes (128 bits) by default |
| 53 | * |
| 54 | * Key: |
| 55 | * The first 32 bytes of the SHA-512 hash of the shared secret |
| 56 | * from the DH key exchange (the latter being expressed as |
| 57 | * the shortest possible big-endian octet string). |
| 58 | * |
| 59 | * The bytes [32,40> of the hash of the shared secret are used for |
| 60 | * initial sequence numbers: [32,36> for those sent by the end without |
| 61 | * setup priority, [36,40> for those for the other end. |
| 62 | * |
| 63 | */ |
| 64 | |
| 65 | #include "secnet.h" |
| 66 | #include "unaligned.h" |
| 67 | #include "util.h" |
| 68 | #include "serpent.h" |
| 69 | #include "sha512.h" |
| 70 | #include "transform-common.h" |
| 71 | #include "hexdebug.h" |
| 72 | |
| 73 | #define BLOCK_SIZE 16 |
| 74 | #define SEQLEN 4 |
| 75 | |
| 76 | struct transform_params { |
| 77 | SEQNUM_PARAMS_FIELDS; |
| 78 | uint32_t tag_length, padding_mask; |
| 79 | }; |
| 80 | |
| 81 | struct transform { |
| 82 | closure_t cl; |
| 83 | struct transform_if ops; |
| 84 | struct transform_params p; |
| 85 | }; |
| 86 | |
| 87 | struct transform_inst { |
| 88 | struct transform_inst_if ops; |
| 89 | struct transform_params p; |
| 90 | /* remaining valid iff keyed */ |
| 91 | unsigned direction:1; |
| 92 | SEQNUM_KEYED_FIELDS; |
| 93 | struct keyInstance key; |
| 94 | uint8_t info_b[BLOCK_SIZE], info_p[BLOCK_SIZE]; |
| 95 | }; |
| 96 | |
| 97 | static void block_encrypt(struct transform_inst *transform_inst, |
| 98 | uint8_t dst[BLOCK_SIZE], |
| 99 | const uint8_t src[BLOCK_SIZE]) |
| 100 | { |
| 101 | serpent_encrypt(&transform_inst->key, src, dst); |
| 102 | } |
| 103 | |
| 104 | #define INFO struct transform_inst *transform_inst |
| 105 | #define I transform_inst |
| 106 | #define EAX_ENTRYPOINT_DECL static |
| 107 | #define BLOCK_ENCRYPT(dst,src) block_encrypt(transform_inst,dst,src) |
| 108 | #define INFO_B (transform_inst->info_b) |
| 109 | #define INFO_P (transform_inst->info_p) |
| 110 | |
| 111 | #include "eax.c" |
| 112 | |
| 113 | #if 0 |
| 114 | |
| 115 | #define TEAX_DEBUG(ary,sz) teax_debug(__func__,__LINE__,#ary,#sz,ary,sz) |
| 116 | static void teax_debug(const char *func, int line, |
| 117 | const char *aryp, const char *szp, |
| 118 | const void *ary, size_t sz) |
| 119 | { |
| 120 | fprintf(stderr,"TEAX %s:%-3d %10s %15s : ", func,line,aryp,szp); |
| 121 | hexdebug(stderr,ary,sz); |
| 122 | fprintf(stderr,"\n"); |
| 123 | } |
| 124 | |
| 125 | #else |
| 126 | |
| 127 | #define TEAX_DEBUG(ary,sz) /* empty */ |
| 128 | |
| 129 | #endif |
| 130 | |
| 131 | static bool_t transform_setkey(void *sst, uint8_t *key, int32_t keylen, |
| 132 | bool_t direction) |
| 133 | { |
| 134 | struct transform_inst *ti=sst; |
| 135 | struct sha512_ctx hash_ctx; |
| 136 | uint8_t hash_out[64]; |
| 137 | |
| 138 | TEAX_DEBUG(key,keylen); |
| 139 | |
| 140 | sha512_init_ctx(&hash_ctx); |
| 141 | sha512_process_bytes(key, keylen, &hash_ctx); |
| 142 | sha512_finish_ctx(&hash_ctx, hash_out); |
| 143 | |
| 144 | TEAX_DEBUG(hash_out,32); |
| 145 | TEAX_DEBUG(hash_out+32,8); |
| 146 | |
| 147 | ti->direction=direction; |
| 148 | serpent_makekey(&ti->key, 32*8, hash_out); |
| 149 | eax_setup(ti); |
| 150 | SEQNUM_KEYED_INIT(get_uint32(hash_out+32+!direction*4), |
| 151 | get_uint32(hash_out+32+direction*4)); |
| 152 | |
| 153 | return True; |
| 154 | } |
| 155 | |
| 156 | TRANSFORM_VALID; |
| 157 | |
| 158 | TRANSFORM_DESTROY; |
| 159 | |
| 160 | static void transform_delkey(void *sst) |
| 161 | { |
| 162 | struct transform_inst *ti=sst; |
| 163 | |
| 164 | FILLZERO(ti->key); |
| 165 | FILLZERO(ti->info_b); |
| 166 | FILLZERO(ti->info_p); |
| 167 | ti->keyed=False; |
| 168 | } |
| 169 | |
| 170 | static transform_apply_return transform_forward(void *sst, |
| 171 | struct buffer_if *buf, const char **errmsg) |
| 172 | { |
| 173 | struct transform_inst *ti=sst; |
| 174 | |
| 175 | KEYED_CHECK; |
| 176 | |
| 177 | size_t padlen = ti->p.padding_mask - buf->size; |
| 178 | padlen &= ti->p.padding_mask; |
| 179 | padlen++; |
| 180 | |
| 181 | uint8_t *pad = buf_append(buf,padlen); |
| 182 | memset(pad, 0, padlen-1); |
| 183 | pad[padlen-1] = padlen; |
| 184 | |
| 185 | uint8_t nonce[SEQLEN+1]; |
| 186 | put_uint32(nonce,ti->sendseq); |
| 187 | nonce[SEQLEN] = ti->direction; |
| 188 | |
| 189 | TEAX_DEBUG(nonce,sizeof(nonce)); |
| 190 | TEAX_DEBUG(buf->start,buf->size); |
| 191 | |
| 192 | assert(buf_append(buf,ti->p.tag_length)); |
| 193 | eax_encrypt(ti, nonce,sizeof(nonce), 0,0, |
| 194 | buf->start,buf->size-ti->p.tag_length, |
| 195 | ti->p.tag_length, buf->start); |
| 196 | |
| 197 | TEAX_DEBUG(buf->start,buf->size); |
| 198 | |
| 199 | BUF_ADD_BYTES(append,buf,nonce,SEQLEN); |
| 200 | |
| 201 | TEAX_DEBUG(nonce,SEQLEN); |
| 202 | |
| 203 | ti->sendseq++; |
| 204 | |
| 205 | return 0; |
| 206 | } |
| 207 | |
| 208 | static transform_apply_return transform_reverse(void *sst, |
| 209 | struct buffer_if *buf, const char **errmsg) |
| 210 | { |
| 211 | struct transform_inst *ti=sst; |
| 212 | |
| 213 | KEYED_CHECK; |
| 214 | |
| 215 | TEAX_DEBUG(buf->start,buf->size); |
| 216 | |
| 217 | uint8_t nonce[SEQLEN+1]; |
| 218 | const uint8_t *seqp = buf_unappend(buf,SEQLEN); |
| 219 | if (!seqp) goto too_short; |
| 220 | |
| 221 | TEAX_DEBUG(seqp,SEQLEN); |
| 222 | |
| 223 | uint32_t seqnum = get_uint32(seqp); |
| 224 | |
| 225 | memcpy(nonce,seqp,SEQLEN); |
| 226 | nonce[4] = !ti->direction; |
| 227 | |
| 228 | TEAX_DEBUG(nonce,sizeof(nonce)); |
| 229 | TEAX_DEBUG(buf->start,buf->size); |
| 230 | |
| 231 | bool_t ok = eax_decrypt(ti, nonce,sizeof(nonce), 0,0, buf->start,buf->size, |
| 232 | ti->p.tag_length, buf->start); |
| 233 | if (!ok) { |
| 234 | TEAX_DEBUG(0,0); |
| 235 | *errmsg="EAX decryption failed"; |
| 236 | return transform_apply_err; |
| 237 | } |
| 238 | assert(buf->size >= (int)ti->p.tag_length); |
| 239 | buf->size -= ti->p.tag_length; |
| 240 | |
| 241 | TEAX_DEBUG(buf->start,buf->size); |
| 242 | |
| 243 | const uint8_t *padp = buf_unappend(buf,1); |
| 244 | if (!padp) goto too_short; |
| 245 | |
| 246 | TEAX_DEBUG(padp,1); |
| 247 | |
| 248 | size_t padlen = *padp; |
| 249 | if (!buf_unappend(buf,padlen-1)) goto too_short; |
| 250 | |
| 251 | SEQNUM_CHECK(seqnum, &ti->p); |
| 252 | |
| 253 | TEAX_DEBUG(buf->start,buf->size); |
| 254 | |
| 255 | return 0; |
| 256 | |
| 257 | too_short: |
| 258 | *errmsg="ciphertext or plaintext too short"; |
| 259 | return transform_apply_err; |
| 260 | } |
| 261 | |
| 262 | static struct transform_inst_if *transform_create(void *sst) |
| 263 | { |
| 264 | struct transform *st=sst; |
| 265 | |
| 266 | TRANSFORM_CREATE_CORE; |
| 267 | |
| 268 | ti->p=st->p; |
| 269 | |
| 270 | return &ti->ops; |
| 271 | } |
| 272 | |
| 273 | static list_t *transform_apply(closure_t *self, struct cloc loc, |
| 274 | dict_t *context, list_t *args) |
| 275 | { |
| 276 | struct transform *st; |
| 277 | item_t *item; |
| 278 | dict_t *dict; |
| 279 | |
| 280 | NEW(st); |
| 281 | st->cl.description="eax-serpent"; |
| 282 | st->cl.type=CL_TRANSFORM; |
| 283 | st->cl.apply=NULL; |
| 284 | st->cl.interface=&st->ops; |
| 285 | st->ops.st=st; |
| 286 | |
| 287 | /* First parameter must be a dict */ |
| 288 | item=list_elem(args,0); |
| 289 | if (!item || item->type!=t_dict) |
| 290 | cfgfatal(loc,"eax-serpent","parameter must be a dictionary\n"); |
| 291 | dict=item->data.dict; |
| 292 | |
| 293 | SET_CAPAB_TRANSFORMNUM(CAPAB_TRANSFORMNUM_EAXSERPENT); |
| 294 | |
| 295 | SEQNUM_PARAMS_INIT(dict,&st->p,"eax-serpent",loc); |
| 296 | |
| 297 | st->p.tag_length=dict_read_number(dict, "tag-length-bytes", |
| 298 | False, "eax-serpent", loc, 128/8); |
| 299 | if (st->p.tag_length<1 || st->p.tag_length>BLOCK_SIZE) |
| 300 | cfgfatal(loc,"eax-serpent","tag-length-bytes out of range 0..%d\n", |
| 301 | BLOCK_SIZE); |
| 302 | |
| 303 | uint32_t padding_round=dict_read_number(dict, "padding-rounding", |
| 304 | False, "eax-serpent", loc, 16); |
| 305 | if (padding_round & (padding_round-1)) |
| 306 | cfgfatal(loc,"eax-serpent","padding-round not a power of two\n"); |
| 307 | if (padding_round > 255) |
| 308 | cfgfatal(loc,"eax-serpent","padding-round must be 1..128\n"); |
| 309 | if (padding_round == 0) |
| 310 | padding_round = 1; |
| 311 | st->p.padding_mask = padding_round-1; |
| 312 | |
| 313 | update_max_start_pad(&transform_max_start_pad, 0); |
| 314 | |
| 315 | st->ops.keylen=0; |
| 316 | st->ops.create=transform_create; |
| 317 | |
| 318 | return new_closure(&st->cl); |
| 319 | } |
| 320 | |
| 321 | void transform_eax_module(dict_t *dict) |
| 322 | { |
| 323 | add_closure(dict,"eax-serpent",transform_apply); |
| 324 | } |