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/* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
/* C port of DumpPublicKey.java from the Android Open source project with
* support for additional RSA key sizes. (platform/system/core,git/libmincrypt
* /tools/DumpPublicKey.java). Uses the OpenSSL X509 and BIGNUM library.
*/
#include <stdint.h>
#include <openssl/bn.h>
#include <openssl/evp.h>
#include <openssl/pem.h>
#include <openssl/x509.h>
#include <string.h>
#include <unistd.h>
/* Command line tool to extract RSA public keys from X.509 certificates
* and output a pre-processed version of keys for use by RSA verification
* routines.
*/
int check(RSA* key) {
int public_exponent = BN_get_word(key->e);
int modulus = BN_num_bits(key->n);
if (public_exponent != 65537) {
fprintf(stderr, "WARNING: Public exponent should be 65537 (but is %d).\n",
public_exponent);
}
if (modulus != 1024 && modulus != 2048 && modulus != 4096
&& modulus != 8192) {
fprintf(stderr, "ERROR: Unknown modulus length = %d.\n", modulus);
return 0;
}
return 1;
}
/* Pre-processes and outputs RSA public key to standard out.
*/
void output(RSA* key) {
int i, nwords;
BIGNUM *N = key->n;
BIGNUM *Big1 = NULL, *Big2 = NULL, *Big32 = NULL, *BigMinus1 = NULL;
BIGNUM *B = NULL;
BIGNUM *N0inv= NULL, *R = NULL, *RR = NULL, *RRTemp = NULL, *NnumBits = NULL;
BIGNUM *n = NULL, *rr = NULL;
BN_CTX *bn_ctx = BN_CTX_new();
uint32_t n0invout;
N = key->n;
/* Output size of RSA key in 32-bit words */
nwords = BN_num_bits(N) / 32;
if (-1 == write(1, &nwords, sizeof(nwords)))
goto failure;
/* Initialize BIGNUMs */
Big1 = BN_new();
Big2 = BN_new();
Big32 = BN_new();
BigMinus1 = BN_new();
N0inv= BN_new();
R = BN_new();
RR = BN_new();
RRTemp = BN_new();
NnumBits = BN_new();
n = BN_new();
rr = BN_new();
BN_set_word(Big1, 1L);
BN_set_word(Big2, 2L);
BN_set_word(Big32, 32L);
BN_sub(BigMinus1, Big1, Big2);
B = BN_new();
BN_exp(B, Big2, Big32, bn_ctx); /* B = 2^32 */
/* Calculate and output N0inv = -1 / N[0] mod 2^32 */
BN_mod_inverse(N0inv, N, B, bn_ctx);
BN_sub(N0inv, B, N0inv);
n0invout = BN_get_word(N0inv);
if (-1 == write(1, &n0invout, sizeof(n0invout)))
goto failure;
/* Calculate R = 2^(# of key bits) */
BN_set_word(NnumBits, BN_num_bits(N));
BN_exp(R, Big2, NnumBits, bn_ctx);
/* Calculate RR = R^2 mod N */
BN_copy(RR, R);
BN_mul(RRTemp, RR, R, bn_ctx);
BN_mod(RR, RRTemp, N, bn_ctx);
/* Write out modulus as little endian array of integers. */
for (i = 0; i < nwords; ++i) {
uint32_t nout;
BN_mod(n, N, B, bn_ctx); /* n = N mod B */
nout = BN_get_word(n);
if (-1 == write(1, &nout, sizeof(nout)))
goto failure;
BN_rshift(N, N, 32); /* N = N/B */
}
/* Write R^2 as little endian array of integers. */
for (i = 0; i < nwords; ++i) {
uint32_t rrout;
BN_mod(rr, RR, B, bn_ctx); /* rr = RR mod B */
rrout = BN_get_word(rr);
if (-1 == write(1, &rrout, sizeof(rrout)))
goto failure;
BN_rshift(RR, RR, 32); /* RR = RR/B */
}
failure:
/* Free BIGNUMs. */
BN_free(Big1);
BN_free(Big2);
BN_free(Big32);
BN_free(BigMinus1);
BN_free(N0inv);
BN_free(R);
BN_free(RRTemp);
BN_free(NnumBits);
BN_free(n);
BN_free(rr);
}
int main(int argc, char* argv[]) {
int cert_mode = 0;
FILE* fp;
X509* cert = NULL;
RSA* pubkey = NULL;
EVP_PKEY* key;
if (argc != 3 || (strcmp(argv[1], "-cert") && strcmp(argv[1], "-pub"))) {
fprintf(stderr, "Usage: %s <-cert | -pub> <file>\n", argv[0]);
return -1;
}
if (!strcmp(argv[1], "-cert"))
cert_mode = 1;
fp = fopen(argv[2], "r");
if (!fp) {
fprintf(stderr, "Couldn't open file %s!\n", argv[2]);
return -1;
}
if (cert_mode) {
/* Read the certificate */
if (!PEM_read_X509(fp, &cert, NULL, NULL)) {
fprintf(stderr, "Couldn't read certificate.\n");
goto fail;
}
/* Get the public key from the certificate. */
key = X509_get_pubkey(cert);
/* Convert to a RSA_style key. */
if (!(pubkey = EVP_PKEY_get1_RSA(key))) {
fprintf(stderr, "Couldn't convert to a RSA style key.\n");
goto fail;
}
} else {
/* Read the pubkey in .PEM format. */
if (!(pubkey = PEM_read_RSA_PUBKEY(fp, NULL, NULL, NULL))) {
fprintf(stderr, "Couldn't read public key file.\n");
goto fail;
}
}
if (check(pubkey)) {
output(pubkey);
}
fail:
X509_free(cert);
RSA_free(pubkey);
fclose(fp);
return 0;
}
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