u-boot/lib/ecdsa/ecdsa-libcrypto.c
Alexandru Gagniuc eb22759e2b lib/ecdsa: Use the 'keydir' argument from mkimage if appropriate
Keys can be derived from keydir, and the "key-name-hint" property of
the FIT. They can also be specified ad-literam via 'keyfile'. Update
the ECDSA signing path to use the appropriate one.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2021-04-14 15:23:01 -04:00

318 lines
8 KiB
C

// 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;
}