1 files changed, 74 insertions, 0 deletions
diff --git a/src/lib/crypt/keyrot.h b/src/lib/crypt/keyrot.h
new file mode 100644
index 00000000..6a598f76
--- /dev/null
+++ b/src/lib/crypt/keyrot.h
@@ -0,0 +1,74 @@
+/*
+ * Ouroboros - Copyright (C) 2016 - 2026
+ *
+ * Data-plane key-rotation schedule (node/leaf keys, selector)
+ *
+ *    Dimitri Staessens <dimitri@ouroboros.rocks>
+ *    Sander Vrijders   <sander@ouroboros.rocks>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * version 2.1 as published by the Free Software Foundation.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., http://www.fsf.org/about/contact/.
+ */
+
+#ifndef OUROBOROS_LIB_CRYPT_KEYROT_H
+#define OUROBOROS_LIB_CRYPT_KEYROT_H
+
+#include <ouroboros/crypt.h>   /* SYMMKEYSZ, NONCESZ */
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#define KR_SELECTOR_LEN 6
+#define KR_NONCE_LEN    NONCESZ
+
+struct keyrot;
+
+struct kr_rx {
+        uint64_t id;   /* batch id of the matched epoch */
+        uint64_t ctr;  /* packet counter for replay check */
+};
+
+struct keyrot * keyrot_create(const uint8_t * root,
+                              uint8_t         epoch,
+                              uint8_t         role);
+
+void            keyrot_destroy(struct keyrot * kr);
+
+int             keyrot_rekey(struct keyrot * kr,
+                             const uint8_t * root,
+                             uint8_t         epoch);
+
+/* Promote TX to the installed (new) batch once the peer is on it. */
+void            keyrot_tx_promote(struct keyrot * kr);
+
+int             keyrot_tx_next(struct keyrot *  kr,
+                               uint8_t          sel[KR_SELECTOR_LEN],
+                               const uint8_t ** key,
+                               uint8_t          nonce[KR_NONCE_LEN]);
+
+int             keyrot_rx_lookup(struct keyrot *  kr,
+                                 const uint8_t    sel[KR_SELECTOR_LEN],
+                                 const uint8_t ** key,
+                                 uint8_t          nonce[KR_NONCE_LEN],
+                                 struct kr_rx *   rx);
+
+/* Commit an authenticated packet: replay window + peer-switched. */
+int             keyrot_rx_commit(struct keyrot *      kr,
+                                 const struct kr_rx * rx);
+
+/* True once an RX packet under the current batch has been observed. */
+bool            keyrot_peer_switched(const struct keyrot * kr);
+
+unsigned        keyrot_tx_nodes_left(struct keyrot * kr);
+
+#endif /* OUROBOROS_LIB_CRYPT_KEYROT_H */