nrf_security: drivers: cracen: Implement Ed25519 in cracenpsa

degjorva · degjorva · commit 833596be4224 · 2025-02-13T15:59:08.000+01:00
Add support for Ed25519 and Ed25519ph in cracenpsa
directly using silexpk/sxsymcrypt.
This bypasses sicrypto, which saves on flash usage
Remove sicrypto implementation of Ed25519 from
being accessible from cracenpsa.

Signed-off-by: Dag Erik Gjørvad &lt;dag.erik.gjorvad@nordicsemi.no&gt;
diff --git a/subsys/nrf_security/src/drivers/cracen/cracenpsa/cracenpsa.cmake b/subsys/nrf_security/src/drivers/cracen/cracenpsa/cracenpsa.cmake
@@ -44,6 +44,7 @@ endif()
 if(CONFIG_PSA_NEED_CRACEN_ASYMMETRIC_SIGNATURE_DRIVER)
   list(APPEND cracen_driver_sources
     ${CMAKE_CURRENT_LIST_DIR}/src/sign.c
+    ${CMAKE_CURRENT_LIST_DIR}/src/ed25519.c
   )
 endif()
 
@@ -90,6 +91,12 @@ if(CONFIG_PSA_NEED_CRACEN_KMU_DRIVER)
   )
 endif()
 
+if(CONFIG_PSA_NEED_CRACEN_KEY_AGREEMENT_DRIVER)
+  list(APPEND cracen_driver_sources
+    ${CMAKE_CURRENT_LIST_DIR}/src/ed25519.c
+  )
+endif()
+
 if(CONFIG_PSA_NEED_CRACEN_KEY_AGREEMENT_DRIVER OR CONFIG_PSA_NEED_CRACEN_KEY_DERIVATION_DRIVER)
   list(APPEND cracen_driver_sources
     ${CMAKE_CURRENT_LIST_DIR}/src/key_derivation.c
diff --git a/subsys/nrf_security/src/drivers/cracen/cracenpsa/include/cracen_psa.h b/subsys/nrf_security/src/drivers/cracen/cracenpsa/include/cracen_psa.h
@@ -361,4 +361,18 @@ psa_status_t cracen_spake2p_get_shared_key(cracen_spake2p_operation_t *operation
 
 psa_status_t cracen_spake2p_abort(cracen_spake2p_operation_t *operation);
 
+int cracen_ed25519_sign(const uint8_t *priv_key, char *signature, const uint8_t *message,
+			size_t message_length);
+
+int cracen_ed25519_verify(const uint8_t *pub_key, const char *message, size_t message_length,
+			  const char *signature);
+
+int cracen_ed25519ph_sign(const uint8_t *priv_key, char *signature, const uint8_t *message,
+			  size_t message_length, bool is_message);
+
+int cracen_ed25519ph_verify(const uint8_t *pub_key, const char *message, size_t message_length,
+			    const char *signature, bool is_message);
+
+int cracen_ed25519_create_pubkey(const uint8_t *priv_key, uint8_t *pub_key);
+
 #endif /* CRACEN_PSA_H */
diff --git a/subsys/nrf_security/src/drivers/cracen/cracenpsa/src/ed25519.c b/subsys/nrf_security/src/drivers/cracen/cracenpsa/src/ed25519.c
@@ -0,0 +1,290 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ *
+ * The comments in this file use the notations and conventions from RFC 8032.
+ *
+ * Workmem layout for an Ed25519 signature verification task:
+ *      1. digest (size: 64 bytes).
+ *
+ * Workmem layout for an Ed25519 signature generation task:
+ *      The workmem is made of 5 areas of 32 bytes each (total size 160 bytes).
+ *      In the following we refer to these areas using the numbers 1 to 5. The
+ *      first hash operation computes the private key's digest, which is stored
+ *      in areas 1 and 2. The second hash operation computes r, which is stored
+ *      in areas 4 and 5. The first point multiplication computes R, which is
+ *      written directly to the output buffer. Then the secret scalar s is
+ *      computed in place in area 1. Area 2 is cleared. The second point
+ *      multiplication computes the public key A, which is stored in area 2. The
+ *      third hash operation computes k, which is stored in areas 2 and 3. The
+ *      final operation (r + k * s) mod L computes S, which is written directly
+ *      to the output buffer.
+ *
+ * Workmem layout for an Ed25519 public key generation task:
+ *      1. digest (size: 64 bytes). The digest of the private key is written in
+ *         this area. Then the secret scalar s is computed in place in the first
+ *         32 bytes of this area.
+ */
+#include <string.h>
+#include <sxsymcrypt/sha2.h>
+#include <silexpk/ed25519.h>
+#include <cracen/ec_helpers.h>
+#include <sxsymcrypt/hash.h>
+#include <cracen/mem_helpers.h>
+#include <cracen/statuscodes.h>
+
+#define AREA2_MEM_OFFSET 32
+#define AREA4_MEM_OFFSET 96
+
+/* This is the ASCII string with the
+ * PHflag 1 and context size 0 appended as defined in:
+ * https://datatracker.ietf.org/doc/html/rfc8032.html#section-2.
+ * It is used for domain separation between Ed25519 and Ed25519ph.
+ * This can not be stored as a const due to hardware limitations
+ */
+static char dom2[] = {0x53, 0x69, 0x67, 0x45, 0x64, 0x32, 0x35, 0x35, 0x31, 0x39, 0x20, 0x6e,
+		      0x6f, 0x20, 0x45, 0x64, 0x32, 0x35, 0x35, 0x31, 0x39, 0x20, 0x63, 0x6f,
+		      0x6c, 0x6c, 0x69, 0x73, 0x69, 0x6f, 0x6e, 0x73, 0x01, 0x00};
+
+static int hash_all_inputs(char const *inputs[], size_t inputs_lengths[], size_t input_count,
+			   const struct sxhashalg *hashalg, char *out)
+{
+	struct sxhash hashopctx;
+	int status;
+
+	status = sx_hash_create(&hashopctx, hashalg, sizeof(hashopctx));
+	if (status != SX_OK) {
+		return status;
+	}
+
+	for (size_t i = 0; i < input_count; i++) {
+		status = sx_hash_feed(&hashopctx, inputs[i], inputs_lengths[i]);
+		if (status != SX_OK) {
+			return status;
+		}
+	}
+	status = sx_hash_digest(&hashopctx, out);
+	if (status != SX_OK) {
+		return status;
+	}
+
+	status = sx_hash_wait(&hashopctx);
+
+	return status;
+}
+
+static int hash_input(const char *input, size_t input_length, char *digest)
+{
+	char const *hash_array[] = {input};
+	size_t hash_array_lengths[] = {input_length};
+
+	return hash_all_inputs(hash_array, hash_array_lengths, 1, &sxhashalg_sha2_512, digest);
+}
+
+static int ed25519_calculate_r(char *workmem, const uint8_t *message, size_t message_length,
+			       bool prehash)
+{
+	char const *hash_array[] = {dom2, workmem, message};
+	size_t hash_array_lengths[] = {sizeof(dom2), SX_ED25519_SZ, message_length};
+	size_t offset = prehash ? 0 : 1;
+	size_t input_count = 3 - offset;
+
+	return hash_all_inputs(&hash_array[offset], &hash_array_lengths[offset], input_count,
+			       &sxhashalg_sha2_512, workmem + SX_ED25519_DGST_SZ);
+}
+
+static int ed25519_calculate_k(char *workmem, char *point_r, const char *message,
+			       size_t message_length, bool prehash)
+{
+	char const *hash_array[] = {dom2, point_r, workmem, message};
+	size_t hash_array_lengths[] = {sizeof(dom2), SX_ED25519_SZ, SX_ED25519_SZ, message_length};
+	size_t offset = prehash ? 0 : 1;
+	size_t input_count = 4 - offset;
+
+	return hash_all_inputs(&hash_array[offset], &hash_array_lengths[offset], input_count,
+			       &sxhashalg_sha2_512, workmem);
+}
+
+static int ed25519_sign_internal(const uint8_t *priv_key, char *signature, const uint8_t *message,
+				 size_t message_length, bool prehash)
+{
+	int status;
+	char workmem[5 * SX_ED25519_SZ];
+	uint8_t pnt_r[SX_ED25519_DGST_SZ];
+	char *area_1 = workmem;
+	char *area_2 = workmem + AREA2_MEM_OFFSET;
+	char *area_4 = workmem + AREA4_MEM_OFFSET;
+
+	/* Hash the private key, the digest is stored in the first 64 bytes of workmem*/
+	status = hash_input(priv_key, SX_ED25519_SZ, area_1);
+	if (status != SX_OK) {
+		return status;
+	}
+
+	/* Obtain r by hashing (prefix || message), where prefix is the second
+	 * half of the private key digest.
+	 */
+	status = ed25519_calculate_r(area_2, message, message_length, prehash);
+	if (status != SX_OK) {
+		return status;
+	}
+
+	/* Perform point multiplication R = [r]B. This is the encoded point R,
+	 * which is the first part of the signature.
+	 */
+	status = sx_ed25519_ptmult((const struct sx_ed25519_dgst *)area_4,
+				   (struct sx_ed25519_pt *)pnt_r);
+	if (status != SX_OK) {
+		return status;
+	}
+
+	/* The secret scalar s is computed in place from the first half of the
+	 * private key digest.
+	 */
+	decode_scalar_25519(area_1);
+
+	/* Clear second half of private key digest: sx_ed25519_ptmult()
+	 * works on an input of SX_ED25519_DGST_SZ bytes.
+	 */
+	safe_memset(area_2, sizeof(workmem) - SX_ED25519_SZ, 0, SX_ED25519_SZ);
+	/* Perform point multiplication A = [s]B,
+	 * to obtain the public key A. which is stored in workmem[32:63]
+	 */
+	status = sx_ed25519_ptmult((const struct sx_ed25519_dgst *)area_1,
+				   (struct sx_ed25519_pt *)area_2);
+
+	if (status != SX_OK) {
+		return status;
+	}
+
+	status = ed25519_calculate_k(area_2, pnt_r, message, message_length, prehash);
+	if (status != SX_OK) {
+		return status;
+	}
+
+	/* Compute (r + k * s) mod L. This gives the second part of the
+	 * signature, which is the encoded S which is stored in pnt_r.
+	 */
+	status = sx_ed25519_sign((const struct sx_ed25519_dgst *)area_2,
+				 (const struct sx_ed25519_dgst *)area_4,
+				 (const struct sx_ed25519_v *)area_1,
+				 (struct sx_ed25519_v *)(pnt_r + SX_ED25519_PT_SZ));
+	if (status != SX_OK) {
+		return status;
+	}
+
+	memcpy(signature, pnt_r, SX_ED25519_DGST_SZ);
+	safe_memzero(workmem, sizeof(workmem));
+
+	return status;
+}
+
+int cracen_ed25519_sign(const uint8_t *priv_key, char *signature, const uint8_t *message,
+			size_t message_length)
+{
+	return ed25519_sign_internal(priv_key, signature, message, message_length, false);
+}
+
+int cracen_ed25519ph_sign(const uint8_t *priv_key, char *signature, const uint8_t *message,
+			  size_t message_length, bool is_message)
+{
+	char hashedmessage[SX_ED25519_DGST_SZ];
+	int status;
+
+	if (is_message) {
+		status = hash_input(message, message_length, hashedmessage);
+		if (status != SX_OK) {
+			return status;
+		}
+
+		return ed25519_sign_internal(priv_key, signature, hashedmessage, SX_ED25519_DGST_SZ,
+					     true);
+	} else {
+		return ed25519_sign_internal(priv_key, signature, message, message_length, true);
+	}
+}
+
+static int ed25519_verify_internal(const uint8_t *pub_key, const char *message,
+				   size_t message_length, const char *signature, bool prehash)
+{
+	int status;
+	char digest[SX_ED25519_DGST_SZ];
+	size_t ed25519_sz = SX_ED25519_SZ;
+	size_t offset = prehash ? 0 : 1;
+	size_t input_count = 4 - offset;
+
+	char const *hash_array[] = {dom2, signature, (const char *)pub_key, message};
+	size_t hash_array_lengths[] = {sizeof(dom2), ed25519_sz, ed25519_sz, message_length};
+
+	status = hash_all_inputs(&hash_array[offset], &hash_array_lengths[offset], input_count,
+				 &sxhashalg_sha2_512, digest);
+	if (status != SX_OK) {
+		return status;
+	}
+
+	status =
+		sx_ed25519_verify((struct sx_ed25519_dgst *)digest, (struct sx_ed25519_pt *)pub_key,
+				  (const struct sx_ed25519_v *)(signature + SX_ED25519_SZ),
+				  (const struct sx_ed25519_pt *)signature);
+
+	return status;
+}
+
+int cracen_ed25519_verify(const uint8_t *pub_key, const char *message, size_t message_length,
+			  const char *signature)
+{
+	return ed25519_verify_internal(pub_key, message, message_length, signature, false);
+}
+
+int cracen_ed25519ph_verify(const uint8_t *pub_key, const char *message, size_t message_length,
+			    const char *signature, bool is_message)
+{
+	int status;
+	char message_digest[SX_ED25519_DGST_SZ];
+
+	if (is_message) {
+		status = hash_input(message, message_length, message_digest);
+		if (status != SX_OK) {
+			return status;
+		}
+
+		return ed25519_verify_internal(pub_key, message_digest, SX_ED25519_DGST_SZ,
+					       signature, true);
+	}
+	return ed25519_verify_internal(pub_key, message, message_length, signature, true);
+}
+
+int cracen_ed25519_create_pubkey(const uint8_t *priv_key, uint8_t *pub_key)
+{
+	int status;
+	char digest[SX_ED25519_DGST_SZ];
+	char *pub_key_A = digest + SX_ED25519_SZ;
+
+	status = hash_input(priv_key, SX_ED25519_SZ, digest);
+	if (status != SX_OK) {
+		return status;
+	}
+	/* The secret scalar s is computed in place from the first half of the
+	 * private key digest.
+	 */
+	decode_scalar_25519(digest);
+
+	/* Clear second half of private key digest: ed25519_ptmult()
+	 * works on an input of SX_ED25519_DGST_SZ bytes.
+	 */
+	safe_memset(pub_key_A, SX_ED25519_SZ, 0, SX_ED25519_SZ);
+
+	/* Perform point multiplication A = [s]B, to obtain the public key A. */
+	status = sx_ed25519_ptmult((const struct sx_ed25519_dgst *)digest,
+				   (struct sx_ed25519_pt *)pub_key_A);
+
+	if (status != SX_OK) {
+		return status;
+	}
+
+	memcpy(pub_key, pub_key_A, SX_ED25519_SZ);
+	safe_memzero(digest, SX_ED25519_DGST_SZ);
+
+	return status;
+}
diff --git a/subsys/nrf_security/src/drivers/cracen/cracenpsa/src/key_management.c b/subsys/nrf_security/src/drivers/cracen/cracenpsa/src/key_management.c
@@ -10,12 +10,9 @@
 #include "cracen_psa.h"
 #include "platform_keys/platform_keys.h"
 #include <nrf_security_mutexes.h>
-
 #include <sicrypto/drbghash.h>
 #include <sicrypto/ecc.h>
 #include <sicrypto/ecdsa.h>
-#include <sicrypto/ed25519.h>
-#include <sicrypto/ed25519ph.h>
 #include <sicrypto/ed448.h>
 #include <sicrypto/montgomery.h>
 #include <sicrypto/rsa_keygen.h>
@@ -603,10 +600,9 @@ static psa_status_t export_ecc_public_key_from_keypair(const psa_key_attributes_
 	psa_status_t psa_status;
 	size_t expected_pub_key_size = 0;
 	int si_status = 0;
-	psa_algorithm_t key_alg = psa_get_key_algorithm(attributes);
 	const struct sx_pk_ecurve *sx_curve;
-	struct sitask t;
 
+	struct sitask t;
 	switch (psa_curve) {
 	case PSA_ECC_FAMILY_BRAINPOOL_P_R1:
 	case PSA_ECC_FAMILY_SECP_R1:
@@ -631,7 +627,6 @@ static psa_status_t export_ecc_public_key_from_keypair(const psa_key_attributes_
 
 	struct si_sig_privkey priv_key;
 	struct si_sig_pubkey pub_key;
-
 	char workmem[SX_ED448_DGST_SZ] = {};
 
 	if (PSA_KEY_LIFETIME_GET_LOCATION(psa_get_key_lifetime(attributes)) ==
@@ -675,24 +670,20 @@ static psa_status_t export_ecc_public_key_from_keypair(const psa_key_attributes_
 			break;
 		case PSA_ECC_FAMILY_TWISTED_EDWARDS:
 			if (key_bits_attr == 255) {
-				if (key_alg == PSA_ALG_ED25519PH) {
-					priv_key.def = si_sig_def_ed25519ph;
-					priv_key.key.ed25519 = (struct sx_ed25519_v *)key_buffer;
-					pub_key.key.ed25519 = (struct sx_ed25519_pt *)data;
+				si_status = cracen_ed25519_create_pubkey(key_buffer, data);
+				if (!si_status) {
+					*data_length = expected_pub_key_size;
+				}
+				return silex_statuscodes_to_psa(si_status);
 				} else {
-					priv_key.def = si_sig_def_ed25519;
-					priv_key.key.ed25519 = (struct sx_ed25519_v *)key_buffer;
-					pub_key.key.ed25519 = (struct sx_ed25519_pt *)data;
+					priv_key.def = si_sig_def_ed448;
+					priv_key.key.ed448 = (struct sx_ed448_v *)key_buffer;
+					pub_key.key.ed448 = (struct sx_ed448_pt *)data;
 				}
-			} else {
-				priv_key.def = si_sig_def_ed448;
-				priv_key.key.ed448 = (struct sx_ed448_v *)key_buffer;
-				pub_key.key.ed448 = (struct sx_ed448_pt *)data;
+				break;
+			default:
+				return PSA_ERROR_NOT_SUPPORTED;
 			}
-			break;
-		default:
-			return PSA_ERROR_NOT_SUPPORTED;
-		}
 	}
 
 	si_task_init(&t, workmem, sizeof(workmem));
diff --git a/subsys/nrf_security/src/drivers/cracen/cracenpsa/src/sign.c b/subsys/nrf_security/src/drivers/cracen/cracenpsa/src/sign.c
