RSA signature verification and SHA-1/256/512 reference implementation for verified boot.

src/platform/vboot_reference/utils/dumpRSAPublicKey.c

+/* 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 <inttypes.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, *Big2, *Big32, *BigMinus1;
+  BIGNUM *B;
+  BIGNUM *N0inv, *R, *RR, *RRTemp, *NnumBits;
+  BIGNUM *n, *rr;
+  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;
+  write(1, &nwords, sizeof(nwords));
+
+  /* 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);
+  write(1, &n0invout, sizeof(n0invout));
+
+  /* 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);
+    write(1, &nout, sizeof(nout));
+
+    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);
+    write(1, &rrout, sizeof(rrout));
+
+    BN_rshift(RR, RR, 32); /* RR = RR/B */
+  }
+
+  /* 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[]) {
+  FILE* fp;
+  X509* cert = NULL;
+  RSA* pubkey = NULL;
+  EVP_PKEY* key;
+
+  if (argc != 2) {
+    fprintf(stderr, "Usage: %s <certfile>\n", argv[0]);
+    return -1;
+  }
+
+  fp = fopen(argv[1], "r");
+
+  if (!fp) {
+    fprintf(stderr, "Couldn't open certificate file!\n");
+    return -1;
+  }
+
+  /* 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;
+  }
+
+  if (check(pubkey)) {
+    output (pubkey);
+  }
+
+fail:
+  X509_free(cert);
+  RSA_free(pubkey);
+  fclose(fp);
+
+  return 0;
+}