File Coverage

src/rsa/rsa_pkcs1_sig_pad.c

Criterion	Covered	Total	%
statement	23	31	74.1
branch	2	6	33.3
condition			n/a
subroutine			n/a
pod			n/a
total	25	37	67.5

line	stmt	bran	code
1			/*
2			* Copyright (c) 2017 Thomas Pornin
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			/* see inner.h */
28			uint32_t
29	2		br_rsa_pkcs1_sig_pad(const unsigned char *hash_oid,
30			const unsigned char *hash, size_t hash_len,
31			uint32_t n_bitlen, unsigned char *x)
32			{
33			size_t u, x3, xlen;
34
35			/*
36			* Padded hash value has format:
37			* 00 01 FF .. FF 00 30 x1 30 x2 06 x3 OID 05 00 04 x4 HASH
38			*
39			* with the following rules:
40			*
41			* -- Total length is equal to the modulus length (unsigned
42			* encoding).
43			*
44			* -- There must be at least eight bytes of value 0xFF.
45			*
46			* -- x4 is equal to the hash length (hash_len).
47			*
48			* -- x3 is equal to the encoded OID value length (hash_oid[0]).
49			*
50			* -- x2 = x3 + 4.
51			*
52			* -- x1 = x2 + x4 + 4 = x3 + x4 + 8.
53			*
54			* Note: the "05 00" is optional (signatures with and without
55			* that sequence exist in practice), but notes in PKCS#1 seem to
56			* indicate that the presence of that sequence (specifically,
57			* an ASN.1 NULL value for the hash parameters) may be slightly
58			* more "standard" than the opposite.
59			*/
60	2		xlen = (n_bitlen + 7) >> 3;
61
62	2	50	if (hash_oid == NULL) {
63	0	0	if (xlen < hash_len + 11) {
64	0		return 0;
65			}
66	0		x[0] = 0x00;
67	0		x[1] = 0x01;
68	0		u = xlen - hash_len;
69	0		memset(x + 2, 0xFF, u - 3);
70	0		x[u - 1] = 0x00;
71			} else {
72	2		x3 = hash_oid[0];
73
74			/*
75			* Check that there is enough room for all the elements,
76			* including at least eight bytes of value 0xFF.
77			*/
78	2	50	if (xlen < (x3 + hash_len + 21)) {
79	0		return 0;
80			}
81	2		x[0] = 0x00;
82	2		x[1] = 0x01;
83	2		u = xlen - x3 - hash_len - 11;
84	2		memset(x + 2, 0xFF, u - 2);
85	2		x[u] = 0x00;
86	2		x[u + 1] = 0x30;
87	2		x[u + 2] = x3 + hash_len + 8;
88	2		x[u + 3] = 0x30;
89	2		x[u + 4] = x3 + 4;
90	2		x[u + 5] = 0x06;
91	2		memcpy(x + u + 6, hash_oid, x3 + 1);
92	2		u += x3 + 7;
93	2		x[u ++] = 0x05;
94	2		x[u ++] = 0x00;
95	2		x[u ++] = 0x04;
96	2		x[u ++] = hash_len;
97			}
98	2		memcpy(x + u, hash, hash_len);
99	2		return 1;
100			}