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- // SPDX-License-Identifier: GPL-2.0+
- /*
- * ECDSA image signing implementation using libcrypto backend
- *
- * The signature is a binary representation of the (R, S) points, padded to the
- * key size. The signature will be (2 * key_size_bits) / 8 bytes.
- *
- * Deviations from behavior of RSA equivalent:
- * - Verification uses private key. This is not technically required, but a
- * limitation on how clumsy the openssl API is to use.
- * - Handling of keys and key paths:
- * - The '-K' key directory option must contain path to the key file,
- * instead of the key directory.
- * - No assumptions are made about the file extension of the key
- * - The 'key-name-hint' property is only used for naming devicetree nodes,
- * but is not used for looking up keys on the filesystem.
- *
- * Copyright (c) 2020,2021, Alexandru Gagniuc <mr.nuke.me@gmail.com>
- */
- #include <u-boot/ecdsa.h>
- #include <u-boot/fdt-libcrypto.h>
- #include <openssl/ssl.h>
- #include <openssl/ec.h>
- #include <openssl/bn.h>
- /* Image signing context for openssl-libcrypto */
- struct signer {
- EVP_PKEY *evp_key; /* Pointer to EVP_PKEY object */
- EC_KEY *ecdsa_key; /* Pointer to EC_KEY object */
- void *hash; /* Pointer to hash used for verification */
- void *signature; /* Pointer to output signature. Do not free()!*/
- };
- static int alloc_ctx(struct signer *ctx, const struct image_sign_info *info)
- {
- memset(ctx, 0, sizeof(*ctx));
- if (!OPENSSL_init_ssl(0, NULL)) {
- fprintf(stderr, "Failure to init SSL library\n");
- return -1;
- }
- ctx->hash = malloc(info->checksum->checksum_len);
- ctx->signature = malloc(info->crypto->key_len * 2);
- if (!ctx->hash || !ctx->signature)
- return -ENOMEM;
- return 0;
- }
- static void free_ctx(struct signer *ctx)
- {
- if (ctx->ecdsa_key)
- EC_KEY_free(ctx->ecdsa_key);
- if (ctx->evp_key)
- EVP_PKEY_free(ctx->evp_key);
- if (ctx->hash)
- free(ctx->hash);
- }
- /*
- * Convert an ECDSA signature to raw format
- *
- * openssl DER-encodes 'binary' signatures. We want the signature in a raw
- * (R, S) point pair. So we have to dance a bit.
- */
- static void ecdsa_sig_encode_raw(void *buf, const ECDSA_SIG *sig, size_t order)
- {
- int point_bytes = order;
- const BIGNUM *r, *s;
- uintptr_t s_buf;
- ECDSA_SIG_get0(sig, &r, &s);
- s_buf = (uintptr_t)buf + point_bytes;
- BN_bn2binpad(r, buf, point_bytes);
- BN_bn2binpad(s, (void *)s_buf, point_bytes);
- }
- /* Get a signature from a raw encoding */
- static ECDSA_SIG *ecdsa_sig_from_raw(void *buf, size_t order)
- {
- int point_bytes = order;
- uintptr_t s_buf;
- ECDSA_SIG *sig;
- BIGNUM *r, *s;
- sig = ECDSA_SIG_new();
- if (!sig)
- return NULL;
- s_buf = (uintptr_t)buf + point_bytes;
- r = BN_bin2bn(buf, point_bytes, NULL);
- s = BN_bin2bn((void *)s_buf, point_bytes, NULL);
- ECDSA_SIG_set0(sig, r, s);
- return sig;
- }
- /* ECDSA key size in bytes */
- static size_t ecdsa_key_size_bytes(const EC_KEY *key)
- {
- const EC_GROUP *group;
- group = EC_KEY_get0_group(key);
- return EC_GROUP_order_bits(group) / 8;
- }
- static int read_key(struct signer *ctx, const char *key_name)
- {
- FILE *f = fopen(key_name, "r");
- if (!f) {
- fprintf(stderr, "Can not get key file '%s'\n", key_name);
- return -ENOENT;
- }
- ctx->evp_key = PEM_read_PrivateKey(f, NULL, NULL, NULL);
- fclose(f);
- if (!ctx->evp_key) {
- fprintf(stderr, "Can not read key from '%s'\n", key_name);
- return -EIO;
- }
- if (EVP_PKEY_id(ctx->evp_key) != EVP_PKEY_EC) {
- fprintf(stderr, "'%s' is not an ECDSA key\n", key_name);
- return -EINVAL;
- }
- ctx->ecdsa_key = EVP_PKEY_get1_EC_KEY(ctx->evp_key);
- if (!ctx->ecdsa_key)
- fprintf(stderr, "Can not extract ECDSA key\n");
- return (ctx->ecdsa_key) ? 0 : -EINVAL;
- }
- /* Prepare a 'signer' context that's ready to sign and verify. */
- static int prepare_ctx(struct signer *ctx, const struct image_sign_info *info)
- {
- int key_len_bytes, ret;
- char kname[1024];
- memset(ctx, 0, sizeof(*ctx));
- if (info->keyfile) {
- snprintf(kname, sizeof(kname), "%s", info->keyfile);
- } else if (info->keydir && info->keyname) {
- snprintf(kname, sizeof(kname), "%s/%s.pem", info->keydir,
- info->keyname);
- } else {
- fprintf(stderr, "keyfile, keyname, or key-name-hint missing\n");
- return -EINVAL;
- }
- ret = alloc_ctx(ctx, info);
- if (ret)
- return ret;
- ret = read_key(ctx, kname);
- if (ret)
- return ret;
- key_len_bytes = ecdsa_key_size_bytes(ctx->ecdsa_key);
- if (key_len_bytes != info->crypto->key_len) {
- fprintf(stderr, "Expected a %u-bit key, got %u-bit key\n",
- info->crypto->key_len * 8, key_len_bytes * 8);
- return -EINVAL;
- }
- return 0;
- }
- static int do_sign(struct signer *ctx, struct image_sign_info *info,
- const struct image_region region[], int region_count)
- {
- const struct checksum_algo *algo = info->checksum;
- ECDSA_SIG *sig;
- algo->calculate(algo->name, region, region_count, ctx->hash);
- sig = ECDSA_do_sign(ctx->hash, algo->checksum_len, ctx->ecdsa_key);
- ecdsa_sig_encode_raw(ctx->signature, sig, info->crypto->key_len);
- return 0;
- }
- static int ecdsa_check_signature(struct signer *ctx, struct image_sign_info *info)
- {
- ECDSA_SIG *sig;
- int okay;
- sig = ecdsa_sig_from_raw(ctx->signature, info->crypto->key_len);
- if (!sig)
- return -ENOMEM;
- okay = ECDSA_do_verify(ctx->hash, info->checksum->checksum_len,
- sig, ctx->ecdsa_key);
- if (!okay)
- fprintf(stderr, "WARNING: Signature is fake news!\n");
- ECDSA_SIG_free(sig);
- return !okay;
- }
- static int do_verify(struct signer *ctx, struct image_sign_info *info,
- const struct image_region region[], int region_count,
- uint8_t *raw_sig, uint sig_len)
- {
- const struct checksum_algo *algo = info->checksum;
- if (sig_len != info->crypto->key_len * 2) {
- fprintf(stderr, "Signature has wrong length\n");
- return -EINVAL;
- }
- memcpy(ctx->signature, raw_sig, sig_len);
- algo->calculate(algo->name, region, region_count, ctx->hash);
- return ecdsa_check_signature(ctx, info);
- }
- int ecdsa_sign(struct image_sign_info *info, const struct image_region region[],
- int region_count, uint8_t **sigp, uint *sig_len)
- {
- struct signer ctx;
- int ret;
- ret = prepare_ctx(&ctx, info);
- if (ret >= 0) {
- do_sign(&ctx, info, region, region_count);
- *sigp = ctx.signature;
- *sig_len = info->crypto->key_len * 2;
- ret = ecdsa_check_signature(&ctx, info);
- }
- free_ctx(&ctx);
- return ret;
- }
- int ecdsa_verify(struct image_sign_info *info,
- const struct image_region region[], int region_count,
- uint8_t *sig, uint sig_len)
- {
- struct signer ctx;
- int ret;
- ret = prepare_ctx(&ctx, info);
- if (ret >= 0)
- ret = do_verify(&ctx, info, region, region_count, sig, sig_len);
- free_ctx(&ctx);
- return ret;
- }
- static int do_add(struct signer *ctx, void *fdt, const char *key_node_name)
- {
- int signature_node, key_node, ret, key_bits;
- const char *curve_name;
- const EC_GROUP *group;
- const EC_POINT *point;
- BIGNUM *x, *y;
- signature_node = fdt_subnode_offset(fdt, 0, FIT_SIG_NODENAME);
- if (signature_node < 0) {
- fprintf(stderr, "Could not find 'signature node: %s\n",
- fdt_strerror(signature_node));
- return signature_node;
- }
- key_node = fdt_add_subnode(fdt, signature_node, key_node_name);
- if (key_node < 0) {
- fprintf(stderr, "Could not create '%s' node: %s\n",
- key_node_name, fdt_strerror(key_node));
- return key_node;
- }
- group = EC_KEY_get0_group(ctx->ecdsa_key);
- key_bits = EC_GROUP_order_bits(group);
- curve_name = OBJ_nid2sn(EC_GROUP_get_curve_name(group));
- /* Let 'x' and 'y' memory leak by not BN_free()'ing them. */
- x = BN_new();
- y = BN_new();
- point = EC_KEY_get0_public_key(ctx->ecdsa_key);
- EC_POINT_get_affine_coordinates(group, point, x, y, NULL);
- ret = fdt_setprop_string(fdt, key_node, "ecdsa,curve", curve_name);
- if (ret < 0)
- return ret;
- ret = fdt_add_bignum(fdt, key_node, "ecdsa,x-point", x, key_bits);
- if (ret < 0)
- return ret;
- ret = fdt_add_bignum(fdt, key_node, "ecdsa,y-point", y, key_bits);
- if (ret < 0)
- return ret;
- return 0;
- }
- int ecdsa_add_verify_data(struct image_sign_info *info, void *fdt)
- {
- const char *fdt_key_name;
- struct signer ctx;
- int ret;
- fdt_key_name = info->keyname ? info->keyname : "default-key";
- ret = prepare_ctx(&ctx, info);
- if (ret >= 0)
- do_add(&ctx, fdt, fdt_key_name);
- free_ctx(&ctx);
- return ret;
- }
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