mdw@git.distorted.org.uk Git - secnet/blob - transform-eax.c

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