[PATCH v5 03/15] ecdsa: initial support of ecdsa using mbedtls
Philippe Reynes
philippe.reynes at softathome.com
Tue Apr 21 23:09:42 CEST 2026
Adds an initial support of ecdsa verify using mbedtls.
Signed-off-by: Philippe Reynes <philippe.reynes at softathome.com>
---
v2:
- rename sw_ecdsa.c to ecdsa.c
v3:
- rename sw_ecdsa_verify to ecdsa_hash_verify
- stop on first group found
- check signature len
- use debug instead of printf
- check function returns
- fix memleaks in ecdsa_hash_verify
v4:
- move struct ecdsa_public_key from ecdsa-u-class.h to internal/ecdsa.h
- use DIV_ROUND_UP
- some code cleanup
v5:
- add kerneldoc header for ecdsa_hash_verify
- read error when setting Q.Z
include/crypto/ecdsa-uclass.h | 15 +---
include/crypto/internal/ecdsa.h | 39 +++++++++
lib/mbedtls/Makefile | 3 +
lib/mbedtls/ecdsa.c | 146 ++++++++++++++++++++++++++++++++
4 files changed, 189 insertions(+), 14 deletions(-)
create mode 100644 include/crypto/internal/ecdsa.h
create mode 100644 lib/mbedtls/ecdsa.c
diff --git a/include/crypto/ecdsa-uclass.h b/include/crypto/ecdsa-uclass.h
index 189843820a0..047a5eda2fc 100644
--- a/include/crypto/ecdsa-uclass.h
+++ b/include/crypto/ecdsa-uclass.h
@@ -4,20 +4,7 @@
*/
#include <dm/device.h>
-
-/**
- * struct ecdsa_public_key - ECDSA public key properties
- *
- * The struct has pointers to the (x, y) curve coordinates to an ECDSA public
- * key, as well as the name of the ECDSA curve. The size of the key is inferred
- * from the 'curve_name'
- */
-struct ecdsa_public_key {
- const char *curve_name; /* Name of curve, e.g. "prime256v1" */
- const void *x; /* x coordinate of public key */
- const void *y; /* y coordinate of public key */
- unsigned int size_bits; /* key size in bits, derived from curve name */
-};
+#include <crypto/internal/ecdsa.h>
struct ecdsa_ops {
/**
diff --git a/include/crypto/internal/ecdsa.h b/include/crypto/internal/ecdsa.h
new file mode 100644
index 00000000000..fe00797c5b0
--- /dev/null
+++ b/include/crypto/internal/ecdsa.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2026, Philippe Reynes <philippe.reynes at softathome.com>
+ */
+#ifndef _ECDSA_HELPER_
+#define _ECDSA_HELPER_
+
+#include <linux/types.h>
+
+/**
+ * struct ecdsa_public_key - ECDSA public key properties
+ *
+ * The struct has pointers to the (x, y) curve coordinates to an ECDSA public
+ * key, as well as the name of the ECDSA curve. The size of the key is inferred
+ * from the 'curve_name'
+ */
+struct ecdsa_public_key {
+ const char *curve_name; /* Name of curve, e.g. "prime256v1" */
+ const void *x; /* x coordinate of public key */
+ const void *y; /* y coordinate of public key */
+ unsigned int size_bits; /* key size in bits, derived from curve name */
+};
+
+/**
+ *
+ * ecdsa_hash_verify() - Verify the ecdsa signature of a hash
+ *
+ * @pubkey : ecdsa public key
+ * @hash : Hash
+ * @hash_len : Size of the hash
+ * @signature : Signature
+ * @sig_len : Size of the signature
+ * Return: 0 if all verified ok, <0 on error
+ */
+int ecdsa_hash_verify(const struct ecdsa_public_key *pubkey,
+ const void *hash, size_t hash_len,
+ const void *signature, size_t sig_len);
+
+#endif
diff --git a/lib/mbedtls/Makefile b/lib/mbedtls/Makefile
index a24c8389744..33698c92282 100644
--- a/lib/mbedtls/Makefile
+++ b/lib/mbedtls/Makefile
@@ -11,6 +11,9 @@ obj-$(CONFIG_$(PHASE_)SHA1_MBEDTLS) += sha1.o
obj-$(CONFIG_$(PHASE_)SHA256_MBEDTLS) += sha256.o
obj-$(CONFIG_$(PHASE_)SHA512_MBEDTLS) += sha512.o
+# shim layer for ecdsa
+obj-$(CONFIG_$(PHASE_)ECDSA_MBEDTLS) += ecdsa.o
+
# x509 libraries
obj-$(CONFIG_$(PHASE_)ASYMMETRIC_PUBLIC_KEY_MBEDTLS) += \
public_key.o
diff --git a/lib/mbedtls/ecdsa.c b/lib/mbedtls/ecdsa.c
new file mode 100644
index 00000000000..90c9c37e96e
--- /dev/null
+++ b/lib/mbedtls/ecdsa.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2026 Philippe Reynes <philippe.reynes at softathome.com>
+ */
+
+#include <log.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include <crypto/internal/ecdsa.h>
+
+#include "mbedtls_options.h" /* required to access private fields */
+#include <mbedtls/ecdsa.h>
+#include <mbedtls/ecp.h>
+
+static mbedtls_ecp_group_id ecdsa_search_group_id(const char *curve_name)
+{
+ mbedtls_ecp_group_id grp_id = MBEDTLS_ECP_DP_NONE;
+ const mbedtls_ecp_curve_info *info;
+
+ if (!curve_name)
+ goto out;
+
+ if (!strcmp(curve_name, "prime256v1"))
+ return MBEDTLS_ECP_DP_SECP256R1;
+
+ info = mbedtls_ecp_curve_list();
+ while (info && info->name) {
+ if (!strcmp(curve_name, info->name)) {
+ grp_id = info->grp_id;
+ break;
+ }
+ info++;
+ }
+
+ out:
+ return grp_id;
+}
+
+int ecdsa_hash_verify(const struct ecdsa_public_key *pubkey,
+ const void *hash, size_t hash_len,
+ const void *signature, size_t sig_len)
+{
+ mbedtls_ecp_group_id grp_id;
+ mbedtls_ecp_group grp;
+ mbedtls_ecp_point Q;
+ mbedtls_mpi r, s;
+ int key_len;
+ int err = -1;
+
+ key_len = DIV_ROUND_UP(pubkey->size_bits, 8);
+
+ /* check the signature len */
+ if (sig_len != 2 * key_len) {
+ log_debug("sig len should be twice the key len (sig len = %zu, key len = %d)\n",
+ sig_len, key_len);
+ err = -EINVAL;
+ goto out;
+ }
+
+ /* search the group */
+ grp_id = ecdsa_search_group_id(pubkey->curve_name);
+ if (grp_id == MBEDTLS_ECP_DP_NONE) {
+ log_debug("curve name %s not found\n", pubkey->curve_name);
+ err = -EINVAL;
+ goto out;
+ }
+
+ /* init and load the group */
+ mbedtls_ecp_group_init(&grp);
+ err = mbedtls_ecp_group_load(&grp, grp_id);
+ if (err) {
+ err = -EINVAL;
+ goto out1;
+ }
+
+ /* prepare the pubkey */
+ mbedtls_ecp_point_init(&Q);
+ err = mbedtls_mpi_read_binary(&Q.X, pubkey->x, key_len);
+ if (err) {
+ log_debug("could not read value x of the public key (err = %d)\n",
+ err);
+ err = -EINVAL;
+ goto out2;
+ }
+ err = mbedtls_mpi_read_binary(&Q.Y, pubkey->y, key_len);
+ if (err) {
+ log_debug("could not read value y of the public key (err = %d)\n",
+ err);
+ err = -EINVAL;
+ goto out2;
+ }
+ err = mbedtls_mpi_lset(&Q.Z, 1);
+ if (err) {
+ log_debug("could not set value z of the public key (err = %d)\n",
+ err);
+ err = -EINVAL;
+ goto out2;
+ }
+
+ /* check if the pubkey is valid */
+ err = mbedtls_ecp_check_pubkey(&grp, &Q);
+ if (err) {
+ log_debug("public key is invalid (err = %d)\n", err);
+ err = -EKEYREJECTED;
+ goto out2;
+ }
+
+ /* compute r */
+ mbedtls_mpi_init(&r);
+ err = mbedtls_mpi_read_binary(&r, signature, key_len);
+ if (err) {
+ log_debug("could not read value r of the signature (err = %d)\n",
+ err);
+ err = -EINVAL;
+ goto out3;
+ }
+
+ /* compute s */
+ mbedtls_mpi_init(&s);
+ err = mbedtls_mpi_read_binary(&s, signature + key_len, key_len);
+ if (err) {
+ log_debug("could not read value s of the signature (err = %d)\n",
+ err);
+ err = -EINVAL;
+ goto out4;
+ }
+
+ /* check the signature */
+ err = mbedtls_ecdsa_verify(&grp, hash, hash_len, &Q, &r, &s);
+ if (err)
+ err = -EINVAL;
+
+ out4:
+ mbedtls_mpi_free(&s);
+ out3:
+ mbedtls_mpi_free(&r);
+ out2:
+ mbedtls_ecp_point_free(&Q);
+ out1:
+ mbedtls_ecp_group_free(&grp);
+ out:
+
+ return err;
+}
--
2.43.0
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