docs: Update with X25519 encrypted images info
Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/docs/design.md b/docs/design.md
index e1045ad..5ff22d1 100644
--- a/docs/design.md
+++ b/docs/design.md
@@ -107,7 +107,8 @@
#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 */
-#define IMAGE_TLV_ENC_EC256 0x32 /* Key encrypted with ECIES P256 */
+#define IMAGE_TLV_ENC_EC256 0x32 /* Key encrypted with ECIES-P256 */
+#define IMAGE_TLV_ENC_X25519 0x33 /* Key encrypted with ECIES-X25519 */
#define IMAGE_TLV_DEPENDENCY 0x40 /* Image depends on other image */
#define IMAGE_TLV_SEC_CNT 0x50 /* security counter */
```