Add bootutil support for ed25519 validation

Signed-off-by: Fabio Utzig <utzig@apache.org>

boot/bootutil/include/bootutil/image.h

@@ -73,6 +73,7 @@ struct flash_area;
 #define IMAGE_TLV_ECDSA224          0x21   /* ECDSA of hash output */
 #define IMAGE_TLV_ECDSA256          0x22   /* ECDSA of hash output */
 #define IMAGE_TLV_RSA3072_PSS       0x23   /* RSA3072 of hash output */
+#define IMAGE_TLV_ED25519           0x24   /* ed25519 of hash output */
 #define IMAGE_TLV_ENC_RSA2048       0x30   /* Key encrypted with RSA-OAEP-2048 */
 #define IMAGE_TLV_ENC_KW128         0x31   /* Key encrypted with AES-KW-128 */
 

boot/bootutil/src/image_ed25519.c

@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#include <string.h>
+
+#include "mcuboot_config/mcuboot_config.h"
+
+#ifdef MCUBOOT_SIGN_ED25519
+#include "bootutil/sign_key.h"
+
+#include "mbedtls/oid.h"
+#include "mbedtls/asn1.h"
+
+#include "bootutil_priv.h"
+
+static const uint8_t ed25519_pubkey_oid[] = MBEDTLS_OID_ISO_IDENTIFIED_ORG "\x65\x70";
+#define NUM_ED25519_BYTES 32
+
+extern int ED25519_verify(const uint8_t *message, size_t message_len,
+                          const uint8_t signature[64],
+                          const uint8_t public_key[32]);
+
+/*
+ * Parse the public key used for signing.
+ */
+static int
+bootutil_import_key(uint8_t **cp, uint8_t *end)
+{
+    size_t len;
+    mbedtls_asn1_buf alg;
+    mbedtls_asn1_buf param;
+
+    if (mbedtls_asn1_get_tag(cp, end, &len,
+        MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) {
+        return -1;
+    }
+    end = *cp + len;
+
+    if (mbedtls_asn1_get_alg(cp, end, &alg, &param)) {
+        return -2;
+    }
+
+    if (alg.len != sizeof(ed25519_pubkey_oid) - 1 ||
+        memcmp(alg.p, ed25519_pubkey_oid, sizeof(ed25519_pubkey_oid) - 1)) {
+        return -3;
+    }
+
+    if (mbedtls_asn1_get_bitstring_null(cp, end, &len)) {
+        return -4;
+    }
+    if (*cp + len != end) {
+        return -5;
+    }
+
+    if (len != NUM_ED25519_BYTES) {
+        return -6;
+    }
+
+    return 0;
+}
+
+int
+bootutil_verify_sig(uint8_t *hash, uint32_t hlen, uint8_t *sig, size_t slen,
+  uint8_t key_id)
+{
+    int rc;
+    uint8_t *pubkey;
+    uint8_t *end;
+
+    if (hlen != 32 || slen != 64) {
+        return -1;
+    }
+
+    pubkey = (uint8_t *)bootutil_keys[key_id].key;
+    end = pubkey + *bootutil_keys[key_id].len;
+
+    rc = bootutil_import_key(&pubkey, end);
+    if (rc) {
+        return -1;
+    }
+
+    rc = ED25519_verify(hash, 32, sig, pubkey);
+    if (rc == 0) {
+        return -2;
+    }
+
+    return 0;
+}
+
+#endif /* MCUBOOT_SIGN_ED25519 */

boot/bootutil/src/image_validate.c

@@ -125,7 +125,8 @@ bootutil_img_hash(struct image_header *hdr, const struct flash_area *fap,
  */
 #if (defined(MCUBOOT_SIGN_RSA)      + \
      defined(MCUBOOT_SIGN_EC)       + \
-     defined(MCUBOOT_SIGN_EC256)) > 1
+     defined(MCUBOOT_SIGN_EC256)    + \
+     defined(MCUBOOT_SIGN_ED25519)) > 1
 #error "Only a single signature type is supported!"
 #endif
 
@@ -147,6 +148,10 @@ bootutil_img_hash(struct image_header *hdr, const struct flash_area *fap,
 #    define EXPECTED_SIG_TLV IMAGE_TLV_ECDSA256
 #    define SIG_BUF_SIZE 128
 #    define EXPECTED_SIG_LEN(x) ((x) >= 72) /* oids + 2 * 32 bytes */
+#elif defined(MCUBOOT_SIGN_ED25519)
+#    define EXPECTED_SIG_TLV IMAGE_TLV_ED25519
+#    define SIG_BUF_SIZE 64
+#    define EXPECTED_SIG_LEN(x) ((x) == SIG_BUF_SIZE)
 #else
 #    define SIG_BUF_SIZE 32 /* no signing, sha256 digest only */
 #endif

root-ed25519.pem

@@ -0,0 +1,3 @@
+-----BEGIN PRIVATE KEY-----
+MC4CAQAwBQYDK2VwBCIEICjJcMmhqKi8d3hoYtLnbQ1DCitXyHz8N5BLy6rIdMvY
+-----END PRIVATE KEY-----