caps: Add cap for x25519 based image encryption

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

boot/bootutil/include/bootutil/caps.h

@@ -45,6 +45,7 @@ uint32_t bootutil_get_caps(void);
 #define BOOTUTIL_CAP_ENC_EC256              (1<<10)
 #define BOOTUTIL_CAP_SWAP_USING_MOVE        (1<<11)
 #define BOOTUTIL_CAP_DOWNGRADE_PREVENTION   (1<<12)
+#define BOOTUTIL_CAP_ENC_X25519             (1<<13)
 
 /*
  * Query the number of images this bootloader is configured for.  This

boot/bootutil/src/caps.c

@@ -54,6 +54,9 @@ uint32_t bootutil_get_caps(void)
 #if defined(MCUBOOT_ENCRYPT_EC256)
     res |= BOOTUTIL_CAP_ENC_EC256;
 #endif
+#if defined(MCUBOOT_ENCRYPT_X25519)
+    res |= BOOTUTIL_CAP_ENC_X25519;
+#endif
 #if defined(MCUBOOT_VALIDATE_PRIMARY_SLOT)
     res |= BOOTUTIL_CAP_VALIDATE_PRIMARY_SLOT;
 #endif

sim/src/caps.rs

@@ -23,6 +23,7 @@ pub enum Caps {
     EncEc256             = (1 << 10),
     SwapUsingMove        = (1 << 11),
     DowngradePrevention  = (1 << 12),
+    EncX25519            = (1 << 13),
 }
 
 impl Caps {