1 /* Copyright 2010 The ChromiumOS Authors
2 * Use of this source code is governed by a BSD-style license that can be
3 * found in the LICENSE file.
4 */
5
6 /* C port of DumpPublicKey.java from the Android Open source project with
7 * support for additional RSA key sizes. (platform/system/core,git/libmincrypt
8 * /tools/DumpPublicKey.java). Uses the OpenSSL X509 and BIGNUM library.
9 */
10
11 #include <openssl/pem.h>
12
13 #include <stdint.h>
14 #include <string.h>
15 #include <unistd.h>
16
17 #include "openssl_compat.h"
18
19 /* Command line tool to extract RSA public keys from X.509 certificates
20 * and output a pre-processed version of keys for use by RSA verification
21 * routines.
22 */
23
check(RSA * key)24 static int check(RSA* key) {
25 const BIGNUM *n, *e;
26 int public_exponent, modulus;
27
28 RSA_get0_key(key, &n, &e, NULL);
29 public_exponent = BN_get_word(e);
30 modulus = BN_num_bits(n);
31
32 if (public_exponent != 3 && public_exponent != 65537) {
33 fprintf(stderr,
34 "WARNING: Public exponent should be 3 or 65537 (but is %d).\n",
35 public_exponent);
36 }
37
38 if (modulus != 1024 && modulus != 2048 && modulus != 3072 && modulus != 4096
39 && modulus != 8192) {
40 fprintf(stderr, "ERROR: Unknown modulus length = %d.\n", modulus);
41 return 0;
42 }
43 return 1;
44 }
45
46 /* Pre-processes and outputs RSA public key to standard out.
47 */
output(RSA * key)48 static void output(RSA* key) {
49 int i, nwords;
50 const BIGNUM *key_n;
51 BIGNUM *N = NULL;
52 BIGNUM *Big1 = NULL, *Big2 = NULL, *Big32 = NULL, *BigMinus1 = NULL;
53 BIGNUM *B = NULL;
54 BIGNUM *N0inv= NULL, *R = NULL, *RR = NULL, *RRTemp = NULL, *NnumBits = NULL;
55 BIGNUM *n = NULL, *rr = NULL;
56 BN_CTX *bn_ctx = BN_CTX_new();
57 uint32_t n0invout;
58
59 /* Output size of RSA key in 32-bit words */
60 nwords = RSA_size(key) / 4;
61 if (-1 == write(1, &nwords, sizeof(nwords)))
62 goto failure;
63
64
65 /* Initialize BIGNUMs */
66 RSA_get0_key(key, &key_n, NULL, NULL);
67 N = BN_dup(key_n);
68 Big1 = BN_new();
69 Big2 = BN_new();
70 Big32 = BN_new();
71 BigMinus1 = BN_new();
72 N0inv= BN_new();
73 R = BN_new();
74 RR = BN_new();
75 RRTemp = BN_new();
76 NnumBits = BN_new();
77 n = BN_new();
78 rr = BN_new();
79
80
81 BN_set_word(Big1, 1L);
82 BN_set_word(Big2, 2L);
83 BN_set_word(Big32, 32L);
84 BN_sub(BigMinus1, Big1, Big2);
85
86 B = BN_new();
87 BN_exp(B, Big2, Big32, bn_ctx); /* B = 2^32 */
88
89 /* Calculate and output N0inv = -1 / N[0] mod 2^32 */
90 BN_mod_inverse(N0inv, N, B, bn_ctx);
91 BN_sub(N0inv, B, N0inv);
92 n0invout = BN_get_word(N0inv);
93 if (-1 == write(1, &n0invout, sizeof(n0invout)))
94 goto failure;
95
96 /* Calculate R = 2^(# of key bits) */
97 BN_set_word(NnumBits, BN_num_bits(N));
98 BN_exp(R, Big2, NnumBits, bn_ctx);
99
100 /* Calculate RR = R^2 mod N */
101 BN_copy(RR, R);
102 BN_mul(RRTemp, RR, R, bn_ctx);
103 BN_mod(RR, RRTemp, N, bn_ctx);
104
105
106 /* Write out modulus as little endian array of integers. */
107 for (i = 0; i < nwords; ++i) {
108 uint32_t nout;
109
110 BN_mod(n, N, B, bn_ctx); /* n = N mod B */
111 nout = BN_get_word(n);
112 if (-1 == write(1, &nout, sizeof(nout)))
113 goto failure;
114
115 BN_rshift(N, N, 32); /* N = N/B */
116 }
117
118 /* Write R^2 as little endian array of integers. */
119 for (i = 0; i < nwords; ++i) {
120 uint32_t rrout;
121
122 BN_mod(rr, RR, B, bn_ctx); /* rr = RR mod B */
123 rrout = BN_get_word(rr);
124 if (-1 == write(1, &rrout, sizeof(rrout)))
125 goto failure;
126
127 BN_rshift(RR, RR, 32); /* RR = RR/B */
128 }
129
130 failure:
131 /* Free BIGNUMs. */
132 BN_free(N);
133 BN_free(Big1);
134 BN_free(Big2);
135 BN_free(Big32);
136 BN_free(BigMinus1);
137 BN_free(N0inv);
138 BN_free(R);
139 BN_free(RRTemp);
140 BN_free(NnumBits);
141 BN_free(n);
142 BN_free(rr);
143
144 }
145
main(int argc,char * argv[])146 int main(int argc, char* argv[]) {
147 int cert_mode = 0;
148 FILE* fp;
149 X509* cert = NULL;
150 RSA* pubkey = NULL;
151 EVP_PKEY* key;
152 char *progname;
153
154 if (argc != 3 || (strcmp(argv[1], "-cert") && strcmp(argv[1], "-pub"))) {
155 progname = strrchr(argv[0], '/');
156 if (progname)
157 progname++;
158 else
159 progname = argv[0];
160 fprintf(stderr, "Usage: %s <-cert | -pub> <file>\n", progname);
161 return -1;
162 }
163
164 if (!strcmp(argv[1], "-cert"))
165 cert_mode = 1;
166
167 fp = fopen(argv[2], "r");
168
169 if (!fp) {
170 fprintf(stderr, "Couldn't open file %s!\n", argv[2]);
171 return -1;
172 }
173
174 if (cert_mode) {
175 /* Read the certificate */
176 if (!PEM_read_X509(fp, &cert, NULL, NULL)) {
177 fprintf(stderr, "Couldn't read certificate.\n");
178 goto fail;
179 }
180
181 /* Get the public key from the certificate. */
182 key = X509_get_pubkey(cert);
183
184 /* Convert to a RSA_style key. */
185 if (!(pubkey = EVP_PKEY_get1_RSA(key))) {
186 fprintf(stderr, "Couldn't convert to a RSA style key.\n");
187 goto fail;
188 }
189 } else {
190 /* Read the pubkey in .PEM format. */
191 if (!(pubkey = PEM_read_RSA_PUBKEY(fp, NULL, NULL, NULL))) {
192 fprintf(stderr, "Couldn't read public key file.\n");
193 goto fail;
194 }
195 }
196
197 if (check(pubkey)) {
198 output(pubkey);
199 }
200
201 fail:
202 X509_free(cert);
203 RSA_free(pubkey);
204 fclose(fp);
205
206 return 0;
207 }
208