2 * eax-transform.c: EAX-Serpent bulk data transformation
4 * We use EAX with the following parameters:
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.
16 * Transmitted message:
19 * 32-bit sequence number (initially zero)
20 * The sequence number allows us to discard far-too-old
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)
33 * 16 bytes (128 bits) by default
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).
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.
47 #include "unaligned.h"
51 #include "transform-common.h"
57 struct transform_params
{
59 uint32_t tag_length
, padding_mask
;
64 struct transform_if ops
;
65 struct transform_params p
;
68 struct transform_inst
{
69 struct transform_inst_if ops
;
70 struct transform_params p
;
71 /* remaining valid iff keyed */
74 struct keyInstance key
;
75 uint8_t info_b
[BLOCK_SIZE
], info_p
[BLOCK_SIZE
];
78 static void block_encrypt(struct transform_inst
*transform_inst
,
79 uint8_t dst
[BLOCK_SIZE
],
80 const uint8_t src
[BLOCK_SIZE
])
82 serpent_encrypt(&transform_inst
->key
, src
, dst
);
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)
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
)
101 fprintf(stderr
,"TEAX %s:%-3d %10s %15s : ", func
,line
,aryp
,szp
);
102 hexdebug(stderr
,ary
,sz
);
103 fprintf(stderr
,"\n");
108 #define TEAX_DEBUG(ary,sz) /* empty */
112 static bool_t
transform_setkey(void *sst
, uint8_t *key
, int32_t keylen
,
115 struct transform_inst
*ti
=sst
;
116 struct sha512_ctx hash_ctx
;
117 uint8_t hash_out
[64];
119 TEAX_DEBUG(key
,keylen
);
121 sha512_init_ctx(&hash_ctx
);
122 sha512_process_bytes(key
, keylen
, &hash_ctx
);
123 sha512_finish_ctx(&hash_ctx
, hash_out
);
125 TEAX_DEBUG(hash_out
,32);
126 TEAX_DEBUG(hash_out
+32,8);
128 ti
->direction
=direction
;
129 serpent_makekey(&ti
->key
, 32*8, hash_out
);
131 SEQNUM_KEYED_INIT(get_uint32(hash_out
+32+!direction
*4),
132 get_uint32(hash_out
+32+direction
*4));
141 static void transform_delkey(void *sst
)
143 struct transform_inst
*ti
=sst
;
146 FILLZERO(ti
->info_b
);
147 FILLZERO(ti
->info_p
);
151 static uint32_t transform_forward(void *sst
, struct buffer_if
*buf
,
154 struct transform_inst
*ti
=sst
;
158 size_t padlen
= ti
->p
.padding_mask
- buf
->size
;
159 padlen
&= ti
->p
.padding_mask
;
162 uint8_t *pad
= buf_append(buf
,padlen
);
163 memset(pad
, 0, padlen
-1);
164 pad
[padlen
-1] = padlen
;
166 uint8_t nonce
[SEQLEN
+1];
167 put_uint32(nonce
,ti
->sendseq
);
168 nonce
[SEQLEN
] = ti
->direction
;
170 TEAX_DEBUG(nonce
,sizeof(nonce
));
171 TEAX_DEBUG(buf
->start
,buf
->size
);
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
);
178 TEAX_DEBUG(buf
->start
,buf
->size
);
180 BUF_ADD_BYTES(append
,buf
,nonce
,SEQLEN
);
182 TEAX_DEBUG(nonce
,SEQLEN
);
189 static uint32_t transform_reverse(void *sst
, struct buffer_if
*buf
,
192 struct transform_inst
*ti
=sst
;
196 TEAX_DEBUG(buf
->start
,buf
->size
);
198 uint8_t nonce
[SEQLEN
+1];
199 const uint8_t *seqp
= buf_unappend(buf
,SEQLEN
);
200 if (!seqp
) goto too_short
;
202 TEAX_DEBUG(seqp
,SEQLEN
);
204 uint32_t seqnum
= get_uint32(seqp
);
206 memcpy(nonce
,seqp
,SEQLEN
);
207 nonce
[4] = !ti
->direction
;
209 TEAX_DEBUG(nonce
,sizeof(nonce
));
210 TEAX_DEBUG(buf
->start
,buf
->size
);
212 bool_t ok
= eax_decrypt(ti
, nonce
,sizeof(nonce
), 0,0, buf
->start
,buf
->size
,
213 ti
->p
.tag_length
, buf
->start
);
216 *errmsg
="EAX decryption failed";
219 assert(buf
->size
>= (int)ti
->p
.tag_length
);
220 buf
->size
-= ti
->p
.tag_length
;
222 TEAX_DEBUG(buf
->start
,buf
->size
);
224 const uint8_t *padp
= buf_unappend(buf
,1);
225 if (!padp
) goto too_short
;
229 size_t padlen
= *padp
;
230 if (!buf_unappend(buf
,padlen
-1)) goto too_short
;
232 SEQNUM_CHECK(seqnum
, &ti
->p
);
234 TEAX_DEBUG(buf
->start
,buf
->size
);
239 *errmsg
="ciphertext or plaintext too short";
243 static struct transform_inst_if
*transform_create(void *sst
)
245 struct transform
*st
=sst
;
247 TRANSFORM_CREATE_CORE
;
254 static list_t
*transform_apply(closure_t
*self
, struct cloc loc
,
255 dict_t
*context
, list_t
*args
)
257 struct transform
*st
;
262 st
->cl
.description
="eax-serpent";
263 st
->cl
.type
=CL_TRANSFORM
;
265 st
->cl
.interface
=&st
->ops
;
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
;
274 SET_CAPAB_TRANSFORMNUM(CAPAB_TRANSFORMNUM_EAXSERPENT
);
276 SEQNUM_PARAMS_INIT(dict
,&st
->p
,"eax-serpent",loc
);
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",
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)
292 st
->p
.padding_mask
= padding_round
-1;
294 update_max_start_pad(&transform_max_start_pad
, 0);
297 st
->ops
.create
=transform_create
;
299 return new_closure(&st
->cl
);
302 void transform_eax_module(dict_t
*dict
)
304 add_closure(dict
,"eax-serpent",transform_apply
);