Add crypto key generation functions

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

platforms/common/include/px4_platform_common/crypto_backend.h

@@ -73,6 +73,7 @@ size_t keystore_get_key(keystore_session_handle_t handle, uint8_t idx, uint8_t *
 
 /*
  * Store a key persistently into the keystore
+ * handle: a handle to an open keystore
  * idx: key index in keystore
  * key: pointer to the key
  * key_size: size of the key
@@ -105,6 +106,17 @@ crypto_session_handle_t crypto_open(px4_crypto_algorithm_t algorithm);
 
 void crypto_close(crypto_session_handle_t *handle);
 
+/*
+ * Generate a key
+ * handle: Open handle for the crypto session. The key will be generated for
+ *         the crypto algorithm used by this session
+ * idx: The key index, by which the key can be used
+ * persistent: if set to "true", the key will be stored into the keystore
+ */
+bool crypto_generate_key(crypto_session_handle_t handle,
+			 uint8_t idx,
+			 bool persistent);
+
 /*
  * Get a key from keystore, possibly encrypted
  *

platforms/common/px4_sw_crypto/sw_crypto/crypto.c

@@ -42,6 +42,7 @@
 #include <stdbool.h>
 
 #include <px4_platform_common/crypto_backend.h>
+#include <px4_random.h>
 #include <lib/crypto/monocypher/src/optional/monocypher-ed25519.h>
 #include <tomcrypt.h>
 
@@ -295,6 +296,48 @@ bool crypto_encrypt_data(crypto_session_handle_t handle,
 	return ret;
 }
 
+bool crypto_generate_key(crypto_session_handle_t handle,
+			 uint8_t idx, bool persistent)
+{
+	bool ret = false;
+
+	if (idx >= KEY_CACHE_LEN) {
+		return false;
+	}
+
+	switch (handle.algorithm) {
+	case CRYPTO_XCHACHA20:
+		if (key_cache[idx].key_size < 32) {
+			if (key_cache[idx].key_size > 0) {
+				SECMEM_FREE(key_cache[idx].key);
+				key_cache[idx].key_size = 0;
+			}
+
+			key_cache[idx].key = SECMEM_ALLOC(32);
+		}
+
+		if (key_cache[idx].key) {
+			key_cache[idx].key_size = 32;
+			px4_get_secure_random(key_cache[idx].key, 32);
+			ret = true;
+
+		} else {
+			key_cache[idx].key_size = 0;
+		}
+
+		break;
+
+	default:
+		break;
+	}
+
+	if (ret && persistent) {
+		keystore_put_key(handle.keystore_handle, idx, key_cache[idx].key, key_cache[idx].key_size);
+	}
+
+	return ret;
+}
+
 bool crypto_get_encrypted_key(crypto_session_handle_t handle,
 			      uint8_t key_idx,
 			      uint8_t *key,