1/*
2 * Copyright (c) 2017 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
27#if BR_INT128 || BR_UMUL128
28
29#if BR_INT128
30
31#define MUL128(hi, lo, x, y)   do { \
32		unsigned __int128 mul128tmp; \
33		mul128tmp = (unsigned __int128)(x) * (unsigned __int128)(y); \
34		(hi) = (uint64_t)(mul128tmp >> 64); \
35		(lo) = (uint64_t)mul128tmp; \
36	} while (0)
37
38#elif BR_UMUL128
39
40#include <intrin.h>
41
42#define MUL128(hi, lo, x, y)   do { \
43		(lo) = _umul128((x), (y), &(hi)); \
44	} while (0)
45
46#endif
47
48#define MASK42   ((uint64_t)0x000003FFFFFFFFFF)
49#define MASK44   ((uint64_t)0x00000FFFFFFFFFFF)
50
51/*
52 * The "accumulator" word is nominally a 130-bit value. We split it into
53 * words of 44 bits, each held in a 64-bit variable.
54 *
55 * If the current accumulator is a = a0 + a1*W + a2*W^2 (where W = 2^44)
56 * and r = r0 + r1*W + r2*W^2, then:
57 *
58 *   a*r = (a0*r0)
59 *       + (a0*r1 + a1*r0) * W
60 *       + (a0*r2 + a1*r1 + a2*r0) * W^2
61 *       + (a1*r2 + a2*r1) * W^3
62 *       + (a2*r2) * W^4
63 *
64 * We want to reduce that value modulo p = 2^130-5, so W^3 = 20 mod p,
65 * and W^4 = 20*W mod p. Thus, if we define u1 = 20*r1 and u2 = 20*r2,
66 * then the equations above become:
67 *
68 *  b0 = a0*r0 + a1*u2 + a2*u1
69 *  b1 = a0*r1 + a1*r0 + a2*u2
70 *  b2 = a0*r2 + a1*r1 + a2*r0
71 *
72 * In order to make u1 fit in 44 bits, we can change these equations
73 * into:
74 *
75 *  b0 = a0*r0 + a1*u2 + a2*t1
76 *  b1 = a0*r1 + a1*r0 + a2*t2
77 *  b2 = a0*r2 + a1*r1 + a2*r0
78 *
79 * Where t1 is u1 truncated to 44 bits, and t2 is u2 added to the extra
80 * bits of u1. Note that since r is clamped down to a 124-bit value, the
81 * values u2 and t2 fit on 44 bits too.
82 *
83 * The bx values are larger than 44 bits, so we may split them into a
84 * lower half (cx, 44 bits) and an upper half (dx). The new values for
85 * the accumulator are then:
86 *
87 *  e0 = c0 + 20*d2
88 *  e1 = c1 + d0
89 *  e2 = c2 + d1
90 *
91 * The equations allow for some room, i.e. the ax values may be larger
92 * than 44 bits. Similarly, the ex values will usually be larger than
93 * the ax. Thus, some sort of carry propagation must be done regularly,
94 * though not necessarily at each iteration. In particular, we do not
95 * need to compute the additions (for the bx values) over 128-bit
96 * quantities; we can stick to 64-bit computations.
97 *
98 *
99 * Since the 128-bit result of a 64x64 multiplication is actually
100 * represented over two 64-bit registers, it is cheaper to arrange for
101 * any split that happens between the "high" and "low" halves to be on
102 * that 64-bit boundary. This is done by left shifting the rx, ux and tx
103 * by 20 bits (since they all fit on 44 bits each, this shift is
104 * always possible).
105 */
106
107static void
108poly1305_inner_big(uint64_t *acc, uint64_t *r, const void *data, size_t len)
109{
110
111#define MX(hi, lo, m0, m1, m2)   do { \
112		uint64_t mxhi, mxlo; \
113		MUL128(mxhi, mxlo, a0, m0); \
114		(hi) = mxhi; \
115		(lo) = mxlo >> 20; \
116		MUL128(mxhi, mxlo, a1, m1); \
117		(hi) += mxhi; \
118		(lo) += mxlo >> 20; \
119		MUL128(mxhi, mxlo, a2, m2); \
120		(hi) += mxhi; \
121		(lo) += mxlo >> 20; \
122	} while (0)
123
124	const unsigned char *buf;
125	uint64_t a0, a1, a2;
126	uint64_t r0, r1, r2, t1, t2, u2;
127
128	r0 = r[0];
129	r1 = r[1];
130	r2 = r[2];
131	t1 = r[3];
132	t2 = r[4];
133	u2 = r[5];
134	a0 = acc[0];
135	a1 = acc[1];
136	a2 = acc[2];
137	buf = data;
138
139	while (len > 0) {
140		uint64_t v0, v1, v2;
141		uint64_t c0, c1, c2, d0, d1, d2;
142
143		v0 = br_dec64le(buf + 0);
144		v1 = br_dec64le(buf + 8);
145		v2 = v1 >> 24;
146		v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
147		v0 &= MASK44;
148		a0 += v0;
149		a1 += v1;
150		a2 += v2 + ((uint64_t)1 << 40);
151		MX(d0, c0, r0, u2, t1);
152		MX(d1, c1, r1, r0, t2);
153		MX(d2, c2, r2, r1, r0);
154		a0 = c0 + 20 * d2;
155		a1 = c1 + d0;
156		a2 = c2 + d1;
157
158		v0 = br_dec64le(buf + 16);
159		v1 = br_dec64le(buf + 24);
160		v2 = v1 >> 24;
161		v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
162		v0 &= MASK44;
163		a0 += v0;
164		a1 += v1;
165		a2 += v2 + ((uint64_t)1 << 40);
166		MX(d0, c0, r0, u2, t1);
167		MX(d1, c1, r1, r0, t2);
168		MX(d2, c2, r2, r1, r0);
169		a0 = c0 + 20 * d2;
170		a1 = c1 + d0;
171		a2 = c2 + d1;
172
173		v0 = br_dec64le(buf + 32);
174		v1 = br_dec64le(buf + 40);
175		v2 = v1 >> 24;
176		v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
177		v0 &= MASK44;
178		a0 += v0;
179		a1 += v1;
180		a2 += v2 + ((uint64_t)1 << 40);
181		MX(d0, c0, r0, u2, t1);
182		MX(d1, c1, r1, r0, t2);
183		MX(d2, c2, r2, r1, r0);
184		a0 = c0 + 20 * d2;
185		a1 = c1 + d0;
186		a2 = c2 + d1;
187
188		v0 = br_dec64le(buf + 48);
189		v1 = br_dec64le(buf + 56);
190		v2 = v1 >> 24;
191		v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
192		v0 &= MASK44;
193		a0 += v0;
194		a1 += v1;
195		a2 += v2 + ((uint64_t)1 << 40);
196		MX(d0, c0, r0, u2, t1);
197		MX(d1, c1, r1, r0, t2);
198		MX(d2, c2, r2, r1, r0);
199		a0 = c0 + 20 * d2;
200		a1 = c1 + d0;
201		a2 = c2 + d1;
202
203		a1 += a0 >> 44;
204		a0 &= MASK44;
205		a2 += a1 >> 44;
206		a1 &= MASK44;
207		a0 += 20 * (a2 >> 44);
208		a2 &= MASK44;
209
210		buf += 64;
211		len -= 64;
212	}
213	acc[0] = a0;
214	acc[1] = a1;
215	acc[2] = a2;
216
217#undef MX
218}
219
220static void
221poly1305_inner_small(uint64_t *acc, uint64_t *r, const void *data, size_t len)
222{
223	const unsigned char *buf;
224	uint64_t a0, a1, a2;
225	uint64_t r0, r1, r2, t1, t2, u2;
226
227	r0 = r[0];
228	r1 = r[1];
229	r2 = r[2];
230	t1 = r[3];
231	t2 = r[4];
232	u2 = r[5];
233	a0 = acc[0];
234	a1 = acc[1];
235	a2 = acc[2];
236	buf = data;
237
238	while (len > 0) {
239		uint64_t v0, v1, v2;
240		uint64_t c0, c1, c2, d0, d1, d2;
241		unsigned char tmp[16];
242
243		if (len < 16) {
244			memcpy(tmp, buf, len);
245			memset(tmp + len, 0, (sizeof tmp) - len);
246			buf = tmp;
247			len = 16;
248		}
249		v0 = br_dec64le(buf + 0);
250		v1 = br_dec64le(buf + 8);
251
252		v2 = v1 >> 24;
253		v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
254		v0 &= MASK44;
255
256		a0 += v0;
257		a1 += v1;
258		a2 += v2 + ((uint64_t)1 << 40);
259
260#define MX(hi, lo, m0, m1, m2)   do { \
261		uint64_t mxhi, mxlo; \
262		MUL128(mxhi, mxlo, a0, m0); \
263		(hi) = mxhi; \
264		(lo) = mxlo >> 20; \
265		MUL128(mxhi, mxlo, a1, m1); \
266		(hi) += mxhi; \
267		(lo) += mxlo >> 20; \
268		MUL128(mxhi, mxlo, a2, m2); \
269		(hi) += mxhi; \
270		(lo) += mxlo >> 20; \
271	} while (0)
272
273		MX(d0, c0, r0, u2, t1);
274		MX(d1, c1, r1, r0, t2);
275		MX(d2, c2, r2, r1, r0);
276
277#undef MX
278
279		a0 = c0 + 20 * d2;
280		a1 = c1 + d0;
281		a2 = c2 + d1;
282
283		a1 += a0 >> 44;
284		a0 &= MASK44;
285		a2 += a1 >> 44;
286		a1 &= MASK44;
287		a0 += 20 * (a2 >> 44);
288		a2 &= MASK44;
289
290		buf += 16;
291		len -= 16;
292	}
293	acc[0] = a0;
294	acc[1] = a1;
295	acc[2] = a2;
296}
297
298static inline void
299poly1305_inner(uint64_t *acc, uint64_t *r, const void *data, size_t len)
300{
301	if (len >= 64) {
302		size_t len2;
303
304		len2 = len & ~(size_t)63;
305		poly1305_inner_big(acc, r, data, len2);
306		data = (const unsigned char *)data + len2;
307		len -= len2;
308	}
309	if (len > 0) {
310		poly1305_inner_small(acc, r, data, len);
311	}
312}
313
314/* see bearssl_block.h */
315void
316br_poly1305_ctmulq_run(const void *key, const void *iv,
317	void *data, size_t len, const void *aad, size_t aad_len,
318	void *tag, br_chacha20_run ichacha, int encrypt)
319{
320	unsigned char pkey[32], foot[16];
321	uint64_t r[6], acc[3], r0, r1;
322	uint32_t v0, v1, v2, v3, v4;
323	uint64_t w0, w1, w2, w3;
324	uint32_t ctl;
325
326	/*
327	 * Compute the MAC key. The 'r' value is the first 16 bytes of
328	 * pkey[].
329	 */
330	memset(pkey, 0, sizeof pkey);
331	ichacha(key, iv, 0, pkey, sizeof pkey);
332
333	/*
334	 * If encrypting, ChaCha20 must run first, followed by Poly1305.
335	 * When decrypting, the operations are reversed.
336	 */
337	if (encrypt) {
338		ichacha(key, iv, 1, data, len);
339	}
340
341	/*
342	 * Run Poly1305. We must process the AAD, then ciphertext, then
343	 * the footer (with the lengths). Note that the AAD and ciphertext
344	 * are meant to be padded with zeros up to the next multiple of 16,
345	 * and the length of the footer is 16 bytes as well.
346	 */
347
348	/*
349	 * Apply the "clamping" on r.
350	 */
351	pkey[ 3] &= 0x0F;
352	pkey[ 4] &= 0xFC;
353	pkey[ 7] &= 0x0F;
354	pkey[ 8] &= 0xFC;
355	pkey[11] &= 0x0F;
356	pkey[12] &= 0xFC;
357	pkey[15] &= 0x0F;
358
359	/*
360	 * Decode the 'r' value into 44-bit words, left-shifted by 20 bits.
361	 * Also compute the u1 and u2 values.
362	 */
363	r0 = br_dec64le(pkey +  0);
364	r1 = br_dec64le(pkey +  8);
365	r[0] = r0 << 20;
366	r[1] = ((r0 >> 24) | (r1 << 40)) & ~(uint64_t)0xFFFFF;
367	r[2] = (r1 >> 4) & ~(uint64_t)0xFFFFF;
368	r1 = 20 * (r[1] >> 20);
369	r[3] = r1 << 20;
370	r[5] = 20 * r[2];
371	r[4] = (r[5] + (r1 >> 24)) & ~(uint64_t)0xFFFFF;
372
373	/*
374	 * Accumulator is 0.
375	 */
376	acc[0] = 0;
377	acc[1] = 0;
378	acc[2] = 0;
379
380	/*
381	 * Process the additional authenticated data, ciphertext, and
382	 * footer in due order.
383	 */
384	br_enc64le(foot, (uint64_t)aad_len);
385	br_enc64le(foot + 8, (uint64_t)len);
386	poly1305_inner(acc, r, aad, aad_len);
387	poly1305_inner(acc, r, data, len);
388	poly1305_inner_small(acc, r, foot, sizeof foot);
389
390	/*
391	 * Finalise modular reduction. At that point, the value consists
392	 * in three 44-bit values (the lowest one might be slightly above
393	 * 2^44). Two loops shall be sufficient.
394	 */
395	acc[1] += (acc[0] >> 44);
396	acc[0] &= MASK44;
397	acc[2] += (acc[1] >> 44);
398	acc[1] &= MASK44;
399	acc[0] += 5 * (acc[2] >> 42);
400	acc[2] &= MASK42;
401	acc[1] += (acc[0] >> 44);
402	acc[0] &= MASK44;
403	acc[2] += (acc[1] >> 44);
404	acc[1] &= MASK44;
405	acc[0] += 5 * (acc[2] >> 42);
406	acc[2] &= MASK42;
407
408	/*
409	 * The value may still fall in the 2^130-5..2^130-1 range, in
410	 * which case we must reduce it again. The code below selects,
411	 * in constant-time, between 'acc' and 'acc-p'. We encode the
412	 * value over four 32-bit integers to finish the operation.
413	 */
414	v0 = (uint32_t)acc[0];
415	v1 = (uint32_t)(acc[0] >> 32) | ((uint32_t)acc[1] << 12);
416	v2 = (uint32_t)(acc[1] >> 20) | ((uint32_t)acc[2] << 24);
417	v3 = (uint32_t)(acc[2] >> 8);
418	v4 = (uint32_t)(acc[2] >> 40);
419
420	ctl = GT(v0, 0xFFFFFFFA);
421	ctl &= EQ(v1, 0xFFFFFFFF);
422	ctl &= EQ(v2, 0xFFFFFFFF);
423	ctl &= EQ(v3, 0xFFFFFFFF);
424	ctl &= EQ(v4, 0x00000003);
425	v0 = MUX(ctl, v0 + 5, v0);
426	v1 = MUX(ctl, 0, v1);
427	v2 = MUX(ctl, 0, v2);
428	v3 = MUX(ctl, 0, v3);
429
430	/*
431	 * Add the "s" value. This is done modulo 2^128. Don't forget
432	 * carry propagation...
433	 */
434	w0 = (uint64_t)v0 + (uint64_t)br_dec32le(pkey + 16);
435	w1 = (uint64_t)v1 + (uint64_t)br_dec32le(pkey + 20) + (w0 >> 32);
436	w2 = (uint64_t)v2 + (uint64_t)br_dec32le(pkey + 24) + (w1 >> 32);
437	w3 = (uint64_t)v3 + (uint64_t)br_dec32le(pkey + 28) + (w2 >> 32);
438	v0 = (uint32_t)w0;
439	v1 = (uint32_t)w1;
440	v2 = (uint32_t)w2;
441	v3 = (uint32_t)w3;
442
443	/*
444	 * Encode the tag.
445	 */
446	br_enc32le((unsigned char *)tag +  0, v0);
447	br_enc32le((unsigned char *)tag +  4, v1);
448	br_enc32le((unsigned char *)tag +  8, v2);
449	br_enc32le((unsigned char *)tag + 12, v3);
450
451	/*
452	 * If decrypting, then ChaCha20 runs _after_ Poly1305.
453	 */
454	if (!encrypt) {
455		ichacha(key, iv, 1, data, len);
456	}
457}
458
459/* see bearssl_block.h */
460br_poly1305_run
461br_poly1305_ctmulq_get(void)
462{
463	return &br_poly1305_ctmulq_run;
464}
465
466#else
467
468/* see bearssl_block.h */
469br_poly1305_run
470br_poly1305_ctmulq_get(void)
471{
472	return 0;
473}
474
475#endif
476