fix(secure-boot): take the verification key from the keystore

eos_image_verify_signature() referenced two symbols that do not exist
anywhere in the repository:

  extern int eos_keystore_get_compiled_key(const uint8_t **key, size_t *len);
  extern const uint8_t ebldr_default_pubkey[32];

The first was declared and never called. The second was assigned straight to
pub_key, and is defined in no translation unit, so any build that links the
signature path failed:

  image_verify.c:(.text+0x404): undefined reference to `ebldr_default_pubkey'

That is why -DEBLDR_BUILD_TESTS=ON did not link.

Beyond not linking, reaching for a raw key symbol bypassed the keystore
entirely — and the keystore is where the security properties live. Its
init() prefers OTP-provisioned keys over the compiled-in one, reads the
revocation flags, picks the first valid non-revoked slot, and seeds the
monotonic security version. get_active_key() then refuses to hand back a slot
that is invalid or revoked. None of that was running: a revoked key would
still have verified images.

Now calls eos_keystore_init() followed by eos_keystore_get_active_key(),
returning EOS_ERR_KEY if either fails, so an unprovisioned or fully revoked
keystore cannot verify anything. The existing dual verification for
fault-injection resistance is unchanged.

With tests enabled the tree now builds with 0 errors and all 11 ctest cases
pass.

Note for deployment, unchanged by this commit: with EBLDR_PRODUCTION_KEY
unset, keystore.c falls back to default_dev_key, which is the RFC 8032 test
vector public key — its private half is public. That fallback is clearly
commented in keystore.c, but it means a default build trusts a key anyone can
sign with. Production builds must define EBLDR_PRODUCTION_KEY and provide
ebldr_production_key, or provision OTP.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: srpatcha

core/image_verify.c

@@ -12,6 +12,7 @@
 
 #include "eos_image.h"
 #include "eos_crypto_boot.h"
+#include "eos_keystore.h"
 #include "eos_hal.h"
 #include <string.h>
 
@@ -130,15 +131,21 @@ int eos_image_verify_signature(const eos_image_header_t *hdr)
 
     /* Phase 2: Ed25519 signature verification */
     if (hdr->sig_type == EOS_SIG_ED25519) {
-        /* Get public key from keystore */
-        extern int eos_keystore_get_compiled_key(const uint8_t **key, size_t *len);
+        /* Take the public key from the keystore rather than reaching for a
+         * symbol directly. Two reasons: ebldr_default_pubkey was never
+         * defined anywhere, so this did not link; and going through the
+         * keystore is what applies OTP provisioning, slot selection and
+         * revocation. A key that has been revoked must not verify anything,
+         * and only eos_keystore_get_active_key() enforces that. */
+        eos_keystore_t ks;
         const uint8_t *pub_key = NULL;
         size_t key_len = 0;
 
-        /* Try compiled-in key directly */
-        extern const uint8_t ebldr_default_pubkey[32];
-        pub_key = ebldr_default_pubkey;
-        key_len = 32;
+        if (eos_keystore_init(&ks) != EOS_OK)
+            return EOS_ERR_KEY;
+
+        if (eos_keystore_get_active_key(&ks, &pub_key, &key_len) != EOS_OK)
+            return EOS_ERR_KEY;
 
         /* Verify signature over the hash */
         int rc = eos_crypto_verify_signature(