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image: Add RSA support for image signing
RSA provides a public key encryption facility which is ideal for image signing and verification. Images are signed using a private key by mkimage. Then at run-time, the images are verified using a private key. This implementation uses openssl for the host part (mkimage). To avoid bringing large libraries into the U-Boot binary, the RSA public key is encoded using a simple numeric representation in the device tree. Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass
Tom Rini
460
lib/rsa/rsa-sign.c
Normal file
460
lib/rsa/rsa-sign.c
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@@ -0,0 +1,460 @@
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/*
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* Copyright (c) 2013, Google Inc.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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* MA 02111-1307 USA
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*/
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#include "mkimage.h"
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#include <stdio.h>
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#include <string.h>
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#include <error.h>
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#include <image.h>
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#include <time.h>
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#include <openssl/rsa.h>
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#include <openssl/pem.h>
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#include <openssl/err.h>
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#include <openssl/ssl.h>
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#include <openssl/evp.h>
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#if OPENSSL_VERSION_NUMBER >= 0x10000000L
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#define HAVE_ERR_REMOVE_THREAD_STATE
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#endif
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static int rsa_err(const char *msg)
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{
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unsigned long sslErr = ERR_get_error();
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fprintf(stderr, "%s", msg);
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fprintf(stderr, ": %s\n",
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ERR_error_string(sslErr, 0));
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return -1;
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}
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/**
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* rsa_get_pub_key() - read a public key from a .crt file
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*
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* @keydir: Directory containins the key
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* @name Name of key file (will have a .crt extension)
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* @rsap Returns RSA object, or NULL on failure
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* @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
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*/
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static int rsa_get_pub_key(const char *keydir, const char *name, RSA **rsap)
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{
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char path[1024];
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EVP_PKEY *key;
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X509 *cert;
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RSA *rsa;
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FILE *f;
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int ret;
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*rsap = NULL;
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snprintf(path, sizeof(path), "%s/%s.crt", keydir, name);
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f = fopen(path, "r");
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if (!f) {
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fprintf(stderr, "Couldn't open RSA certificate: '%s': %s\n",
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path, strerror(errno));
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return -EACCES;
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}
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/* Read the certificate */
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cert = NULL;
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if (!PEM_read_X509(f, &cert, NULL, NULL)) {
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rsa_err("Couldn't read certificate");
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ret = -EINVAL;
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goto err_cert;
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}
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/* Get the public key from the certificate. */
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key = X509_get_pubkey(cert);
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if (!key) {
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rsa_err("Couldn't read public key\n");
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ret = -EINVAL;
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goto err_pubkey;
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}
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/* Convert to a RSA_style key. */
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rsa = EVP_PKEY_get1_RSA(key);
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if (!rsa) {
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rsa_err("Couldn't convert to a RSA style key");
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goto err_rsa;
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}
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fclose(f);
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EVP_PKEY_free(key);
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X509_free(cert);
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*rsap = rsa;
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return 0;
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err_rsa:
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EVP_PKEY_free(key);
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err_pubkey:
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X509_free(cert);
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err_cert:
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fclose(f);
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return ret;
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}
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/**
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* rsa_get_priv_key() - read a private key from a .key file
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*
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* @keydir: Directory containins the key
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* @name Name of key file (will have a .key extension)
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* @rsap Returns RSA object, or NULL on failure
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* @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
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*/
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static int rsa_get_priv_key(const char *keydir, const char *name, RSA **rsap)
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{
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char path[1024];
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RSA *rsa;
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FILE *f;
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*rsap = NULL;
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snprintf(path, sizeof(path), "%s/%s.key", keydir, name);
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f = fopen(path, "r");
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if (!f) {
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fprintf(stderr, "Couldn't open RSA private key: '%s': %s\n",
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path, strerror(errno));
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return -ENOENT;
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}
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rsa = PEM_read_RSAPrivateKey(f, 0, NULL, path);
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if (!rsa) {
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rsa_err("Failure reading private key");
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fclose(f);
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return -EPROTO;
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}
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fclose(f);
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*rsap = rsa;
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return 0;
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}
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static int rsa_init(void)
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{
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int ret;
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ret = SSL_library_init();
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if (!ret) {
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fprintf(stderr, "Failure to init SSL library\n");
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return -1;
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}
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SSL_load_error_strings();
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OpenSSL_add_all_algorithms();
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OpenSSL_add_all_digests();
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OpenSSL_add_all_ciphers();
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return 0;
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}
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static void rsa_remove(void)
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{
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CRYPTO_cleanup_all_ex_data();
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ERR_free_strings();
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#ifdef HAVE_ERR_REMOVE_THREAD_STATE
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ERR_remove_thread_state(NULL);
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#else
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ERR_remove_state(0);
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#endif
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EVP_cleanup();
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}
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static int rsa_sign_with_key(RSA *rsa, const struct image_region region[],
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int region_count, uint8_t **sigp, uint *sig_size)
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{
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EVP_PKEY *key;
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EVP_MD_CTX *context;
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int size, ret = 0;
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uint8_t *sig;
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int i;
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key = EVP_PKEY_new();
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if (!key)
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return rsa_err("EVP_PKEY object creation failed");
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if (!EVP_PKEY_set1_RSA(key, rsa)) {
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ret = rsa_err("EVP key setup failed");
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goto err_set;
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}
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size = EVP_PKEY_size(key);
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sig = malloc(size);
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if (!sig) {
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fprintf(stderr, "Out of memory for signature (%d bytes)\n",
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size);
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ret = -ENOMEM;
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goto err_alloc;
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}
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context = EVP_MD_CTX_create();
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if (!context) {
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ret = rsa_err("EVP context creation failed");
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goto err_create;
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}
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EVP_MD_CTX_init(context);
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if (!EVP_SignInit(context, EVP_sha1())) {
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ret = rsa_err("Signer setup failed");
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goto err_sign;
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}
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for (i = 0; i < region_count; i++) {
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if (!EVP_SignUpdate(context, region[i].data, region[i].size)) {
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ret = rsa_err("Signing data failed");
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goto err_sign;
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}
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}
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if (!EVP_SignFinal(context, sig, sig_size, key)) {
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ret = rsa_err("Could not obtain signature");
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goto err_sign;
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}
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EVP_MD_CTX_cleanup(context);
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EVP_MD_CTX_destroy(context);
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EVP_PKEY_free(key);
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debug("Got signature: %d bytes, expected %d\n", *sig_size, size);
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*sigp = sig;
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*sig_size = size;
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return 0;
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err_sign:
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EVP_MD_CTX_destroy(context);
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err_create:
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free(sig);
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err_alloc:
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err_set:
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EVP_PKEY_free(key);
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return ret;
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}
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int rsa_sign(struct image_sign_info *info,
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const struct image_region region[], int region_count,
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uint8_t **sigp, uint *sig_len)
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{
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RSA *rsa;
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int ret;
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ret = rsa_init();
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if (ret)
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return ret;
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ret = rsa_get_priv_key(info->keydir, info->keyname, &rsa);
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if (ret)
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goto err_priv;
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ret = rsa_sign_with_key(rsa, region, region_count, sigp, sig_len);
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if (ret)
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goto err_sign;
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RSA_free(rsa);
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rsa_remove();
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return ret;
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err_sign:
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RSA_free(rsa);
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err_priv:
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rsa_remove();
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return ret;
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}
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/*
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* rsa_get_params(): - Get the important parameters of an RSA public key
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*/
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int rsa_get_params(RSA *key, uint32_t *n0_invp, BIGNUM **modulusp,
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BIGNUM **r_squaredp)
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{
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BIGNUM *big1, *big2, *big32, *big2_32;
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BIGNUM *n, *r, *r_squared, *tmp;
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BN_CTX *bn_ctx = BN_CTX_new();
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int ret = 0;
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/* Initialize BIGNUMs */
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big1 = BN_new();
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big2 = BN_new();
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big32 = BN_new();
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r = BN_new();
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r_squared = BN_new();
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tmp = BN_new();
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big2_32 = BN_new();
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n = BN_new();
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if (!big1 || !big2 || !big32 || !r || !r_squared || !tmp || !big2_32 ||
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!n) {
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fprintf(stderr, "Out of memory (bignum)\n");
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return -ENOMEM;
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}
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if (!BN_copy(n, key->n) || !BN_set_word(big1, 1L) ||
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!BN_set_word(big2, 2L) || !BN_set_word(big32, 32L))
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ret = -1;
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/* big2_32 = 2^32 */
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if (!BN_exp(big2_32, big2, big32, bn_ctx))
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ret = -1;
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/* Calculate n0_inv = -1 / n[0] mod 2^32 */
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if (!BN_mod_inverse(tmp, n, big2_32, bn_ctx) ||
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!BN_sub(tmp, big2_32, tmp))
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ret = -1;
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*n0_invp = BN_get_word(tmp);
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/* Calculate R = 2^(# of key bits) */
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if (!BN_set_word(tmp, BN_num_bits(n)) ||
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!BN_exp(r, big2, tmp, bn_ctx))
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ret = -1;
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/* Calculate r_squared = R^2 mod n */
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if (!BN_copy(r_squared, r) ||
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!BN_mul(tmp, r_squared, r, bn_ctx) ||
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!BN_mod(r_squared, tmp, n, bn_ctx))
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ret = -1;
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*modulusp = n;
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*r_squaredp = r_squared;
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BN_free(big1);
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BN_free(big2);
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BN_free(big32);
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BN_free(r);
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BN_free(tmp);
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BN_free(big2_32);
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if (ret) {
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fprintf(stderr, "Bignum operations failed\n");
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return -ENOMEM;
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}
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return ret;
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}
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static int fdt_add_bignum(void *blob, int noffset, const char *prop_name,
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BIGNUM *num, int num_bits)
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{
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int nwords = num_bits / 32;
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int size;
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uint32_t *buf, *ptr;
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BIGNUM *tmp, *big2, *big32, *big2_32;
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BN_CTX *ctx;
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int ret;
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tmp = BN_new();
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big2 = BN_new();
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big32 = BN_new();
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big2_32 = BN_new();
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if (!tmp || !big2 || !big32 || !big2_32) {
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fprintf(stderr, "Out of memory (bignum)\n");
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return -ENOMEM;
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}
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ctx = BN_CTX_new();
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if (!tmp) {
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fprintf(stderr, "Out of memory (bignum context)\n");
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return -ENOMEM;
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}
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BN_set_word(big2, 2L);
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BN_set_word(big32, 32L);
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BN_exp(big2_32, big2, big32, ctx); /* B = 2^32 */
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size = nwords * sizeof(uint32_t);
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buf = malloc(size);
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if (!buf) {
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fprintf(stderr, "Out of memory (%d bytes)\n", size);
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return -ENOMEM;
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}
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/* Write out modulus as big endian array of integers */
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for (ptr = buf + nwords - 1; ptr >= buf; ptr--) {
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BN_mod(tmp, num, big2_32, ctx); /* n = N mod B */
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*ptr = cpu_to_fdt32(BN_get_word(tmp));
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BN_rshift(num, num, 32); /* N = N/B */
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}
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ret = fdt_setprop(blob, noffset, prop_name, buf, size);
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if (ret) {
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fprintf(stderr, "Failed to write public key to FIT\n");
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return -ENOSPC;
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}
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free(buf);
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BN_free(tmp);
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BN_free(big2);
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BN_free(big32);
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BN_free(big2_32);
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return ret;
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}
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int rsa_add_verify_data(struct image_sign_info *info, void *keydest)
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{
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BIGNUM *modulus, *r_squared;
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uint32_t n0_inv;
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int parent, node;
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char name[100];
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int ret;
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int bits;
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RSA *rsa;
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debug("%s: Getting verification data\n", __func__);
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ret = rsa_get_pub_key(info->keydir, info->keyname, &rsa);
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if (ret)
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return ret;
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ret = rsa_get_params(rsa, &n0_inv, &modulus, &r_squared);
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if (ret)
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return ret;
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bits = BN_num_bits(modulus);
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parent = fdt_subnode_offset(keydest, 0, FIT_SIG_NODENAME);
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if (parent == -FDT_ERR_NOTFOUND) {
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parent = fdt_add_subnode(keydest, 0, FIT_SIG_NODENAME);
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if (parent < 0) {
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fprintf(stderr, "Couldn't create signature node: %s\n",
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fdt_strerror(parent));
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return -EINVAL;
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}
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}
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/* Either create or overwrite the named key node */
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snprintf(name, sizeof(name), "key-%s", info->keyname);
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node = fdt_subnode_offset(keydest, parent, name);
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if (node == -FDT_ERR_NOTFOUND) {
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node = fdt_add_subnode(keydest, parent, name);
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if (node < 0) {
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fprintf(stderr, "Could not create key subnode: %s\n",
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fdt_strerror(node));
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return -EINVAL;
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}
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} else if (node < 0) {
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fprintf(stderr, "Cannot select keys parent: %s\n",
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fdt_strerror(node));
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return -ENOSPC;
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}
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ret = fdt_setprop_string(keydest, node, "key-name-hint",
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info->keyname);
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ret |= fdt_setprop_u32(keydest, node, "rsa,num-bits", bits);
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ret |= fdt_setprop_u32(keydest, node, "rsa,n0-inverse", n0_inv);
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ret |= fdt_add_bignum(keydest, node, "rsa,modulus", modulus, bits);
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ret |= fdt_add_bignum(keydest, node, "rsa,r-squared", r_squared, bits);
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ret |= fdt_setprop_string(keydest, node, FIT_ALGO_PROP,
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info->algo->name);
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if (info->require_keys) {
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fdt_setprop_string(keydest, node, "required",
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info->require_keys);
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}
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BN_free(modulus);
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BN_free(r_squared);
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if (ret)
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return -EIO;
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return 0;
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}
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