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