[dnssec] key API: add key availability checks

dnssec/src/key.c

@@ -180,6 +180,16 @@ int dnssec_key_get_id(const dnssec_key_t *key, dnssec_key_id_t id)
 	return DNSSEC_EOK;
 }
 
+bool dnssec_key_can_sign(const dnssec_key_t *key)
+{
+	return key && key->private_key;
+}
+
+bool dnssec_key_can_verify(const dnssec_key_t *key)
+{
+	return key && key->public_key;
+}
+
 int dnssec_key_from_params(dnssec_key_t *key, uint16_t flags, uint8_t protocol,
 			   uint8_t algorithm, const dnssec_binary_t *public_key)
 {

dnssec/src/key.h

 #pragma once
 
 #include <gnutls/abstract.h>
+#include <stdbool.h>
 #include <stdint.h>
+
 #include "binary.h"
 #include "shared.h"
 
@@ -57,6 +59,9 @@ uint8_t dnssec_key_get_protocol(const dnssec_key_t *key);
 uint8_t dnssec_key_get_algorithm(const dnssec_key_t *key);
 int dnssec_key_get_pubkey(const dnssec_key_t *key, dnssec_binary_t *pubkey);
 
+bool dnssec_key_can_sign(const dnssec_key_t *key);
+bool dnssec_key_can_verify(const dnssec_key_t *key);
+
 // TODO: PKCS 8
 
 // TODO: PKCS 11