2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
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
28 * This file contains some additional functions for "i15" big integers.
29 * These functions are needed to support RSA.
34 br_i15_decode_reduce(uint16_t *x
,
35 const void *src
, size_t len
, const uint16_t *m
)
37 uint32_t m_ebitlen
, m_rbitlen
;
39 const unsigned char *buf
;
44 * Get the encoded bit length.
49 * Special case for an invalid (null) modulus.
57 * Clear the destination.
59 br_i15_zero(x
, m_ebitlen
);
62 * First decode directly as many bytes as possible. This requires
63 * computing the actual bit length.
65 m_rbitlen
= m_ebitlen
>> 4;
66 m_rbitlen
= (m_ebitlen
& 15) + (m_rbitlen
<< 4) - m_rbitlen
;
67 mblen
= (m_rbitlen
+ 7) >> 3;
70 br_i15_decode(x
, src
, len
);
75 br_i15_decode(x
, buf
, k
);
79 * Input remaining bytes, using 15-bit words.
90 br_i15_muladd_small(x
, acc
>> (acc_len
- 15), m
);
92 acc
&= ~((uint32_t)-1 << acc_len
);
97 * We may have some bits accumulated. We then perform a shift to
98 * be able to inject these bits as a full 15-bit word.
101 acc
= (acc
| (x
[1] << acc_len
)) & 0x7FFF;
102 br_i15_rshift(x
, 15 - acc_len
);
103 br_i15_muladd_small(x
, acc
, m
);
109 br_i15_reduce(uint16_t *x
, const uint16_t *a
, const uint16_t *m
)
111 uint32_t m_bitlen
, a_bitlen
;
112 size_t mlen
, alen
, u
;
115 mlen
= (m_bitlen
+ 15) >> 4;
123 * If the source is shorter, then simply copy all words from a[]
124 * and zero out the upper words.
127 alen
= (a_bitlen
+ 15) >> 4;
128 if (a_bitlen
< m_bitlen
) {
129 memcpy(x
+ 1, a
+ 1, alen
* sizeof *a
);
130 for (u
= alen
; u
< mlen
; u
++) {
137 * The source length is at least equal to that of the modulus.
138 * We must thus copy N-1 words, and input the remaining words
141 memcpy(x
+ 1, a
+ 2 + (alen
- mlen
), (mlen
- 1) * sizeof *a
);
143 for (u
= 1 + alen
- mlen
; u
> 0; u
--) {
144 br_i15_muladd_small(x
, a
[u
], m
);
150 br_i15_mulacc(uint16_t *d
, const uint16_t *a
, const uint16_t *b
)
152 size_t alen
, blen
, u
;
154 alen
= (a
[0] + 15) >> 4;
155 blen
= (b
[0] + 15) >> 4;
157 for (u
= 0; u
< blen
; u
++) {
164 for (v
= 0; v
< alen
; v
++) {
167 z
= (uint32_t)d
[1 + u
+ v
] + MUL15(f
, a
[1 + v
]) + cc
;
169 d
[1 + u
+ v
] = z
& 0x7FFF;
171 d
[1 + u
+ alen
] = cc
;