1 /* rsa_e_3.c
2 **
3 ** Copyright 2008, The Android Open Source Project
4 **
5 ** Redistribution and use in source and binary forms, with or without
6 ** modification, are permitted provided that the following conditions are met:
7 ** * Redistributions of source code must retain the above copyright
8 ** notice, this list of conditions and the following disclaimer.
9 ** * Redistributions in binary form must reproduce the above copyright
10 ** notice, this list of conditions and the following disclaimer in the
11 ** documentation and/or other materials provided with the distribution.
12 ** * Neither the name of Google Inc. nor the names of its contributors may
13 ** be used to endorse or promote products derived from this software
14 ** without specific prior written permission.
15 **
16 ** THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS OR
17 ** IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
18 ** MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
19 ** EVENT SHALL Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
20 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
21 ** PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
22 ** OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
23 ** WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
24 ** OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
25 ** ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include "mincrypt/rsa.h"
29 #include "mincrypt/sha.h"
30
31 /* a[] -= mod */
subM(const RSAPublicKey * key,uint32_t * a)32 static void subM(const RSAPublicKey *key, uint32_t *a) {
33 int64_t A = 0;
34 int i;
35 for (i = 0; i < key->len; ++i) {
36 A += (uint64_t)a[i] - key->n[i];
37 a[i] = (uint32_t)A;
38 A >>= 32;
39 }
40 }
41
42 /* return a[] >= mod */
geM(const RSAPublicKey * key,const uint32_t * a)43 static int geM(const RSAPublicKey *key, const uint32_t *a) {
44 int i;
45 for (i = key->len; i;) {
46 --i;
47 if (a[i] < key->n[i]) return 0;
48 if (a[i] > key->n[i]) return 1;
49 }
50 return 1; /* equal */
51 }
52
53 /* montgomery c[] += a * b[] / R % mod */
montMulAdd(const RSAPublicKey * key,uint32_t * c,const uint32_t a,const uint32_t * b)54 static void montMulAdd(const RSAPublicKey *key,
55 uint32_t* c,
56 const uint32_t a,
57 const uint32_t* b) {
58 uint64_t A = (uint64_t)a * b[0] + c[0];
59 uint32_t d0 = (uint32_t)A * key->n0inv;
60 uint64_t B = (uint64_t)d0 * key->n[0] + (uint32_t)A;
61 int i;
62
63 for (i = 1; i < key->len; ++i) {
64 A = (A >> 32) + (uint64_t)a * b[i] + c[i];
65 B = (B >> 32) + (uint64_t)d0 * key->n[i] + (uint32_t)A;
66 c[i - 1] = (uint32_t)B;
67 }
68
69 A = (A >> 32) + (B >> 32);
70
71 c[i - 1] = (uint32_t)A;
72
73 if (A >> 32) {
74 subM(key, c);
75 }
76 }
77
78 /* montgomery c[] = a[] * b[] / R % mod */
montMul(const RSAPublicKey * key,uint32_t * c,const uint32_t * a,const uint32_t * b)79 static void montMul(const RSAPublicKey *key,
80 uint32_t* c,
81 const uint32_t* a,
82 const uint32_t* b) {
83 int i;
84 for (i = 0; i < key->len; ++i) {
85 c[i] = 0;
86 }
87 for (i = 0; i < key->len; ++i) {
88 montMulAdd(key, c, a[i], b);
89 }
90 }
91
92 /* In-place public exponentiation.
93 ** Input and output big-endian byte array in inout.
94 */
modpow3(const RSAPublicKey * key,uint8_t * inout)95 static void modpow3(const RSAPublicKey *key,
96 uint8_t* inout) {
97 uint32_t a[RSANUMWORDS];
98 uint32_t aR[RSANUMWORDS];
99 uint32_t aaR[RSANUMWORDS];
100 uint32_t *aaa = aR; /* Re-use location. */
101 int i;
102
103 /* Convert from big endian byte array to little endian word array. */
104 for (i = 0; i < key->len; ++i) {
105 uint32_t tmp =
106 (inout[((key->len - 1 - i) * 4) + 0] << 24) |
107 (inout[((key->len - 1 - i) * 4) + 1] << 16) |
108 (inout[((key->len - 1 - i) * 4) + 2] << 8) |
109 (inout[((key->len - 1 - i) * 4) + 3] << 0);
110 a[i] = tmp;
111 }
112
113 montMul(key, aR, a, key->rr); /* aR = a * RR / R mod M */
114 montMul(key, aaR, aR, aR); /* aaR = aR * aR / R mod M */
115 montMul(key, aaa, aaR, a); /* aaa = aaR * a / R mod M */
116
117 /* Make sure aaa < mod; aaa is at most 1x mod too large. */
118 if (geM(key, aaa)) {
119 subM(key, aaa);
120 }
121
122 /* Convert to bigendian byte array */
123 for (i = key->len - 1; i >= 0; --i) {
124 uint32_t tmp = aaa[i];
125 *inout++ = tmp >> 24;
126 *inout++ = tmp >> 16;
127 *inout++ = tmp >> 8;
128 *inout++ = tmp >> 0;
129 }
130 }
131
132 /* Expected PKCS1.5 signature padding bytes, for a keytool RSA signature.
133 ** Has the 0-length optional parameter encoded in the ASN1 (as opposed to the
134 ** other flavor which omits the optional parameter entirely). This code does not
135 ** accept signatures without the optional parameter.
136 */
137 static const uint8_t padding[RSANUMBYTES - SHA_DIGEST_SIZE] = {
138 0x00,0x01,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
139 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
140 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
141 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
142 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
143 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
144 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
145 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
146 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
147 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
148 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
149 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
150 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
151 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
152 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
153 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
154 0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0x00,
155 0x30,0x21,0x30,0x09,0x06,0x05,0x2b,0x0e,0x03,0x02,0x1a,0x05,0x00,
156 0x04,0x14
157 };
158
159 /* Verify a 2048 bit RSA e=3 PKCS1.5 signature against an expected SHA-1 hash.
160 ** Returns 0 on failure, 1 on success.
161 */
RSA_e_3_verify(const RSAPublicKey * key,const uint8_t * signature,const int len,const uint8_t * sha)162 int RSA_e_3_verify(const RSAPublicKey *key,
163 const uint8_t *signature,
164 const int len,
165 const uint8_t *sha) {
166 uint8_t buf[RSANUMBYTES];
167 int i;
168
169 if (key->len != RSANUMWORDS) {
170 return 0; /* Wrong key passed in. */
171 }
172
173 if (len != sizeof(buf)) {
174 return 0; /* Wrong input length. */
175 }
176
177 if (key->exponent != 3) {
178 return 0; // Wrong exponent.
179 }
180
181 for (i = 0; i < len; ++i) {
182 buf[i] = signature[i];
183 }
184
185 modpow3(key, buf);
186
187 /* Check pkcs1.5 padding bytes. */
188 for (i = 0; i < (int) sizeof(padding); ++i) {
189 if (buf[i] != padding[i]) {
190 return 0;
191 }
192 }
193
194 /* Check sha digest matches. */
195 for (; i < len; ++i) {
196 if (buf[i] != *sha++) {
197 return 0;
198 }
199 }
200
201 return 1;
202 }
203