[PATCH v1 1/1] lib: ecdsa: Add support for loading ECDSA public key from FDT
Jamin Lin
jamin_lin at aspeedtech.com
Fri Jun 6 09:34:21 CEST 2025
This patch adds support for parsing ECDSA public keys from the device tree
blob (FDT) under the `/signature` node. The public key is expected to be
defined using:
- ecdsa,curve (e.g., "prime256v1", "secp384r1")
- ecdsa,x-point
- ecdsa,y-point
The implementation introduces:
- struct ecdsa_public_key to hold parsed key fields
- fdt_get_key() to parse the curve and coordinates from the FDT
- read_key_from_fdt() to convert the parsed values into an OpenSSL EC_KEY
- load_key_from_fdt() to support loading keys using required_keynode,
keyname hint, or fallback to scanning all subnodes under "/signature".
If "info->fdt_blob" is provided, the key is loaded from the FDT. Otherwise,
the code falls back to loading a PEM-formatted key from file as before.
This allows for ECDSA signature verification where the public key is
embedded in the FIT image device tree, useful for systems that require
signature validation without external files.
Signed-off-by: Jamin Lin <jamin_lin at aspeedtech.com>
---
lib/ecdsa/ecdsa-libcrypto.c | 176 +++++++++++++++++++++++++++++++++++-
1 file changed, 175 insertions(+), 1 deletion(-)
diff --git a/lib/ecdsa/ecdsa-libcrypto.c b/lib/ecdsa/ecdsa-libcrypto.c
index f0095e9dbcf..7415d685ee1 100644
--- a/lib/ecdsa/ecdsa-libcrypto.c
+++ b/lib/ecdsa/ecdsa-libcrypto.c
@@ -34,6 +34,112 @@ struct signer {
void *signature; /* Pointer to output signature. Do not free()!*/
};
+struct ecdsa_public_key {
+ const char *curve_name;
+ const uint8_t *x;
+ const uint8_t *y;
+ int size_bits;
+};
+
+static int fdt_get_key(struct ecdsa_public_key *key, const void *fdt, int node)
+{
+ int x_len;
+ int y_len;
+
+ key->curve_name = fdt_getprop(fdt, node, "ecdsa,curve", NULL);
+ if (!key->curve_name)
+ return -ENOMSG;
+
+ if (!strcmp(key->curve_name, "prime256v1"))
+ key->size_bits = 256;
+ else if (!strcmp(key->curve_name, "secp384r1"))
+ key->size_bits = 384;
+ else
+ return -EINVAL;
+
+ key->x = fdt_getprop(fdt, node, "ecdsa,x-point", &x_len);
+ key->y = fdt_getprop(fdt, node, "ecdsa,y-point", &y_len);
+
+ if (!key->x || !key->y)
+ return -EINVAL;
+
+ if (x_len != key->size_bits / 8 || y_len != key->size_bits / 8)
+ return -EINVAL;
+
+ return 0;
+}
+
+static int read_key_from_fdt(struct signer *ctx, const void *fdt, int node)
+{
+ struct ecdsa_public_key pubkey;
+ const EC_GROUP *group;
+ EC_POINT *point;
+ EC_KEY *ec_key;
+ int ret;
+ int nid;
+ int len;
+
+ ret = fdt_get_key(&pubkey, fdt, node);
+ if (ret) {
+ fprintf(stderr, "Failed to parse ECDSA key from FDT node %d (ret=%d)\n", node, ret);
+ return ret;
+ }
+
+ if (!strcmp(pubkey.curve_name, "prime256v1")) {
+ nid = NID_X9_62_prime256v1;
+ } else if (!strcmp(pubkey.curve_name, "secp384r1")) {
+ nid = NID_secp384r1;
+ } else {
+ fprintf(stderr, "Unsupported curve name: '%s'\n", pubkey.curve_name);
+ return -EINVAL;
+ }
+
+ fprintf(stderr, "Loading ECDSA key: curve=%s, bits=%d\n", pubkey.curve_name,
+ pubkey.size_bits);
+
+ ec_key = EC_KEY_new_by_curve_name(nid);
+ if (!ec_key) {
+ fprintf(stderr, "Failed to allocate EC_KEY for curve %s\n", pubkey.curve_name);
+ return -ENOMEM;
+ }
+
+ group = EC_KEY_get0_group(ec_key);
+ point = EC_POINT_new(group);
+ if (!point) {
+ fprintf(stderr, "Failed to allocate EC_POINT\n");
+ EC_KEY_free(ec_key);
+ return -ENOMEM;
+ }
+
+ len = pubkey.size_bits / 8;
+
+ uint8_t buf[1 + len * 2];
+
+ /* uncompressed */
+ buf[0] = 0x04;
+ memcpy(&buf[1], pubkey.x, len);
+ memcpy(&buf[1 + len], pubkey.y, len);
+ if (!EC_POINT_oct2point(group, point, buf, sizeof(buf), NULL)) {
+ fprintf(stderr, "Failed to convert (x,y) point to EC_POINT\n");
+ EC_POINT_free(point);
+ EC_KEY_free(ec_key);
+ return -EINVAL;
+ }
+
+ if (!EC_KEY_set_public_key(ec_key, point)) {
+ fprintf(stderr, "Failed to set EC_POINT as public key\n");
+ EC_POINT_free(point);
+ EC_KEY_free(ec_key);
+ return -EINVAL;
+ }
+
+ fprintf(stderr, "Successfully loaded ECDSA key from FDT node %d\n", node);
+ EC_POINT_free(point);
+ ctx->ecdsa_key = ec_key;
+
+ return 0;
+}
+
static int alloc_ctx(struct signer *ctx, const struct image_sign_info *info)
{
memset(ctx, 0, sizeof(*ctx));
@@ -153,6 +259,72 @@ static int read_key(struct signer *ctx, const char *key_name)
return (ctx->ecdsa_key) ? 0 : -EINVAL;
}
+static int load_key_from_fdt(struct signer *ctx, const struct image_sign_info *info)
+{
+ const void *fdt = info->fdt_blob;
+ char name[128];
+ int sig_node;
+ int key_node;
+ int key_len;
+ int ret;
+
+ if (!fdt)
+ return -EINVAL;
+
+ ret = alloc_ctx(ctx, info);
+ if (ret)
+ return ret;
+
+ sig_node = fdt_subnode_offset(fdt, 0, FIT_SIG_NODENAME);
+ if (sig_node < 0) {
+ fprintf(stderr, "No /signature node found\n");
+ return -ENOENT;
+ }
+
+ /* Case 1: explicitly specified key node */
+ if (info->required_keynode >= 0) {
+ ret = read_key_from_fdt(ctx, fdt, info->required_keynode);
+ if (ret == 0)
+ goto check_key_len;
+
+ fprintf(stderr, "Failed to load required keynode %d\n", info->required_keynode);
+ return ret;
+ }
+
+ /* Case 2: use keyname hint */
+ if (info->keyname) {
+ snprintf(name, sizeof(name), "%s", info->keyname);
+ key_node = fdt_subnode_offset(fdt, sig_node, name);
+ if (key_node >= 0) {
+ ret = read_key_from_fdt(ctx, fdt, key_node);
+ if (ret == 0)
+ goto check_key_len;
+
+ fprintf(stderr, "Key hint '%s' found but failed to load\n", info->keyname);
+ }
+ }
+
+ /* Case 3: try all subnodes */
+ fdt_for_each_subnode(key_node, fdt, sig_node) {
+ ret = read_key_from_fdt(ctx, fdt, key_node);
+ if (ret == 0)
+ goto check_key_len;
+ }
+
+ fprintf(stderr, "Failed to load any usable ECDSA key from FDT\n");
+ return -EINVAL;
+
+check_key_len:
+ key_len = ecdsa_key_size_bytes(ctx->ecdsa_key);
+ if (key_len != info->crypto->key_len) {
+ fprintf(stderr, "Expected %u-bit key, got %u-bit key\n",
+ info->crypto->key_len * 8, key_len * 8);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
/* Prepare a 'signer' context that's ready to sign and verify. */
static int prepare_ctx(struct signer *ctx, const struct image_sign_info *info)
{
@@ -161,7 +333,9 @@ static int prepare_ctx(struct signer *ctx, const struct image_sign_info *info)
memset(ctx, 0, sizeof(*ctx));
- if (info->keyfile) {
+ if (info->fdt_blob) {
+ return load_key_from_fdt(ctx, info);
+ } else 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,
--
2.43.0
More information about the U-Boot
mailing list