mkimage supports rsa2048, and rsa4096 signatures. With newer silicon now supporting hardware-accelerated ECDSA, it makes sense to expand signing support to elliptic curves.
Implement host-side ECDSA signing and verification with libcrypto. Device-side implementation of signature verification is beyond the scope of this patch. Signed-off-by: Alexandru Gagniuc <[email protected]> --- common/image-sig.c | 14 +- include/u-boot/ecdsa.h | 27 ++++ lib/ecdsa/ecdsa-libcrypto.c | 300 ++++++++++++++++++++++++++++++++++++ tools/Makefile | 3 + 4 files changed, 342 insertions(+), 2 deletions(-) create mode 100644 include/u-boot/ecdsa.h create mode 100644 lib/ecdsa/ecdsa-libcrypto.c diff --git a/common/image-sig.c b/common/image-sig.c index 21dafe6b91..2548b3eb0f 100644 --- a/common/image-sig.c +++ b/common/image-sig.c @@ -15,6 +15,7 @@ DECLARE_GLOBAL_DATA_PTR; #endif /* !USE_HOSTCC*/ #include <image.h> +#include <u-boot/ecdsa.h> #include <u-boot/rsa.h> #include <u-boot/hash-checksum.h> @@ -82,8 +83,17 @@ struct crypto_algo crypto_algos[] = { .sign = rsa_sign, .add_verify_data = rsa_add_verify_data, .verify = rsa_verify, - } - + }, +#if defined(USE_HOSTCC) + /* Currently, only host support exists for ECDSA */ + { + .name = "ecdsa256", + .key_len = ECDSA256_BYTES, + .sign = ecdsa_sign, + .add_verify_data = ecdsa_add_verify_data, + .verify = ecdsa_verify, + }, +#endif }; struct padding_algo padding_algos[] = { diff --git a/include/u-boot/ecdsa.h b/include/u-boot/ecdsa.h new file mode 100644 index 0000000000..a13a7267e1 --- /dev/null +++ b/include/u-boot/ecdsa.h @@ -0,0 +1,27 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Copyright (c) 2020, Alexandru Gagniuc <[email protected]>. + */ + +#ifndef _ECDSA_H +#define _ECDSA_H + +#include <errno.h> +#include <image.h> + +/** + * crypto_algo API impementation for ECDSA; + * @see "struct crypto_algo" + * @{ + */ +int ecdsa_sign(struct image_sign_info *info, const struct image_region region[], + int region_count, uint8_t **sigp, uint *sig_len); +int ecdsa_verify(struct image_sign_info *info, + const struct image_region region[], int region_count, + uint8_t *sig, uint sig_len); +int ecdsa_add_verify_data(struct image_sign_info *info, void *keydest); +/** @} */ + +#define ECDSA256_BYTES (256 / 8) + +#endif diff --git a/lib/ecdsa/ecdsa-libcrypto.c b/lib/ecdsa/ecdsa-libcrypto.c new file mode 100644 index 0000000000..ff491411d0 --- /dev/null +++ b/lib/ecdsa/ecdsa-libcrypto.c @@ -0,0 +1,300 @@ +// 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, Alexandru Gagniuc <[email protected]> + */ + +#include <u-boot/ecdsa.h> +#include <u-boot/fdt-libcrypto.h> +#include <openssl/ssl.h> +#include <openssl/ec.h> +#include <openssl/bn.h> + +struct signer { + EVP_PKEY *evp_key; + EC_KEY *ecdsa_key; + void *hash; + void *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 -1; + + 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); +} + +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; +} + +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 -1; + } + + 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 -1; + } + + if (EVP_PKEY_id(ctx->evp_key) != EVP_PKEY_EC) { + fprintf(stderr, "'%s' is not an ECDSA key\n", key_name); + return -1; + } + + 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 : -1; +} + +static int prepare_ctx(struct signer *ctx, const struct image_sign_info *info) +{ + const char *kname = info->keydir; + int key_len_bytes; + + if (alloc_ctx(ctx, info) < 0) + return -1; + + if (read_key(ctx, kname) < 0) + return -1; + + 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 -1; + } + + 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 -1; + + 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 -1; + } + + 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; +} diff --git a/tools/Makefile b/tools/Makefile index af7698fd01..a4f7b7e80c 100644 --- a/tools/Makefile +++ b/tools/Makefile @@ -70,6 +70,8 @@ RSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/rsa/, \ rsa-sign.o rsa-verify.o \ rsa-mod-exp.o) +ECDSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/ecdsa/, ecdsa-libcrypto.o) + AES_OBJS-$(CONFIG_FIT_CIPHER) := $(addprefix lib/aes/, \ aes-encrypt.o aes-decrypt.o) @@ -119,6 +121,7 @@ dumpimage-mkimage-objs := aisimage.o \ gpimage.o \ gpimage-common.o \ mtk_image.o \ + $(ECDSA_OBJS-y) \ $(RSA_OBJS-y) \ $(AES_OBJS-y) -- 2.26.2
