1/*
2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25#include "inner.h"
26
27static inline size_t
28hash_size(const br_hash_class *dig)
29{
30	return (unsigned)(dig->desc >> BR_HASHDESC_OUT_OFF)
31		& BR_HASHDESC_OUT_MASK;
32}
33
34static inline size_t
35block_size(const br_hash_class *dig)
36{
37	unsigned ls;
38
39	ls = (unsigned)(dig->desc >> BR_HASHDESC_LBLEN_OFF)
40		& BR_HASHDESC_LBLEN_MASK;
41	return (size_t)1 << ls;
42}
43
44/* see bearssl.h */
45size_t
46br_hmac_outCT(const br_hmac_context *ctx,
47	const void *data, size_t len, size_t min_len, size_t max_len,
48	void *out)
49{
50	/*
51	 * Method implemented here is inspired from the descriptions on:
52	 *    https://www.imperialviolet.org/2013/02/04/luckythirteen.html
53	 *
54	 * Principle: we input bytes one by one. We use a MUX to push
55	 * padding bytes instead of data bytes when appropriate. At each
56	 * block limit, we get the current hash function state: this is
57	 * a potential output, since we handle MD padding ourselves.
58	 *
59	 * be     1 for big-endian, 0 for little-endian
60	 * po     minimal MD padding length
61	 * bs     block size (always a power of 2)
62	 * hlen   hash output size
63	 */
64
65	const br_hash_class *dig;
66	br_hash_compat_context hc;
67	int be;
68	uint32_t po, bs;
69	uint32_t kr, km, kl, kz, u;
70	uint64_t count, ncount, bit_len;
71	unsigned char tmp1[64], tmp2[64];
72	size_t hlen;
73
74	/*
75	 * Copy the current hash context.
76	 */
77	hc = ctx->dig;
78
79	/*
80	 * Get function-specific information.
81	 */
82	dig = hc.vtable;
83	be = (dig->desc & BR_HASHDESC_MD_PADDING_BE) != 0;
84	po = 9;
85	if (dig->desc & BR_HASHDESC_MD_PADDING_128) {
86		po += 8;
87	}
88	bs = block_size(dig);
89	hlen = hash_size(dig);
90
91	/*
92	 * Get current input length and compute total bit length.
93	 */
94	count = dig->state(&hc.vtable, tmp1);
95	bit_len = (count + (uint64_t)len) << 3;
96
97	/*
98	 * We can input the blocks that we are sure we will use.
99	 * This offers better performance (no MUX for these blocks)
100	 * and also ensures that the remaining lengths fit on 32 bits.
101	 */
102	ncount = (count + (uint64_t)min_len) & ~(uint64_t)(bs - 1);
103	if (ncount > count) {
104		size_t zlen;
105
106		zlen = (size_t)(ncount - count);
107		dig->update(&hc.vtable, data, zlen);
108		data = (const unsigned char *)data + zlen;
109		len -= zlen;
110		max_len -= zlen;
111		count = ncount;
112	}
113
114	/*
115	 * At that point:
116	 * -- 'count' contains the number of bytes already processed
117	 * (in total).
118	 * -- We must input 'len' bytes. 'min_len' is unimportant: we
119	 * used it to know how many full blocks we could process
120	 * directly. Now only len and max_len matter.
121	 *
122	 * We compute kr, kl, kz and km.
123	 *  kr   number of input bytes already in the current block
124	 *  km   index of the first byte after the end of the last padding
125	 *       block, if length is max_len
126	 *  kz   index of the last byte of the actual last padding block
127	 *  kl   index of the start of the encoded length
128	 *
129	 * km, kz and kl are counted from the current offset in the
130	 * input data.
131	 */
132	kr = (uint32_t)count & (bs - 1);
133	kz = ((kr + (uint32_t)len + po + bs - 1) & ~(bs - 1)) - 1 - kr;
134	kl = kz - 7;
135	km = ((kr + (uint32_t)max_len + po + bs - 1) & ~(bs - 1)) - kr;
136
137	/*
138	 * We must now process km bytes. For index u from 0 to km-1:
139	 *   d is from data[] if u < max_len, 0x00 otherwise
140	 *   e is an encoded length byte or 0x00, depending on u
141	 * The tests for d and e need not be constant-time, since
142	 * they relate only to u and max_len, not to the actual length.
143	 *
144	 * Actual input length is then:
145	 *   d      if u < len
146	 *   0x80   if u == len
147	 *   0x00   if u > len and u < kl
148	 *   e      if u >= kl
149	 *
150	 * Hash state is obtained whenever we reach a full block. This
151	 * is the result we want if and only if u == kz.
152	 */
153	memset(tmp2, 0, sizeof tmp2);
154	for (u = 0; u < km; u ++) {
155		uint32_t v;
156		uint32_t d, e, x0, x1;
157		unsigned char x[1];
158
159		d = (u < max_len) ? ((const unsigned char *)data)[u] : 0x00;
160		v = (kr + u) & (bs - 1);
161		if (v >= (bs - 8)) {
162			unsigned j;
163
164			j = (v - (bs - 8)) << 3;
165			if (be) {
166				e = (uint32_t)(bit_len >> (56 - j));
167			} else {
168				e = (uint32_t)(bit_len >> j);
169			}
170			e &= 0xFF;
171		} else {
172			e = 0x00;
173		}
174		x0 = MUX(EQ(u, (uint32_t)len), 0x80, d);
175		x1 = MUX(LT(u, kl), 0x00, e);
176		x[0] = MUX(LE(u, (uint32_t)len), x0, x1);
177		dig->update(&hc.vtable, x, 1);
178		if (v == (bs - 1)) {
179			dig->state(&hc.vtable, tmp1);
180			CCOPY(EQ(u, kz), tmp2, tmp1, hlen);
181		}
182	}
183
184	/*
185	 * Inner hash output is in tmp2[]; we finish processing.
186	 */
187	dig->init(&hc.vtable);
188	dig->set_state(&hc.vtable, ctx->kso, (uint64_t)bs);
189	dig->update(&hc.vtable, tmp2, hlen);
190	dig->out(&hc.vtable, tmp2);
191	memcpy(out, tmp2, ctx->out_len);
192	return ctx->out_len;
193}
194