1 files changed, 41 insertions, 0 deletions
diff --git a/cmake/config/lib/crypt.cmake b/cmake/config/lib/crypt.cmake
new file mode 100644
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--- /dev/null
+++ b/cmake/config/lib/crypt.cmake
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+# Encryption configuration for Ouroboros Options for the key schedule and packet protection in
+# src/lib/crypt/
+
+# Encryption
+set(KEY_LEAF_BITS 20 CACHE STRING
+  "Packets per leaf key as a power of two (2^20 = AEAD-safe default)")
+set(KEY_NODE_BITS 6 CACHE STRING
+  "Leaf keys per node key, power of two (2^6 = 64; leak compartment)")
+set(KEY_NODE_COUNT 128 CACHE STRING
+  "Node keys per batch (N); <= 4096, the 12-bit on-wire node index")
+set(KEY_REKEY_WATERMARK 4 CACHE STRING
+  "Re-key when this many node keys remain; 0 disables the count trigger")
+set(KEY_REPLAY_WINDOW 2048 CACHE STRING
+  "RX replay window in packets; power of two, >= 128")
+set(KEY_REKEY_WM_CHECK_BITS 16 CACHE STRING
+  "Re-key watermark is consulted once per 2^n flow writes")
+if(NOT KEY_REPLAY_WINDOW MATCHES "^[0-9]+$")
+  message(FATAL_ERROR "KEY_REPLAY_WINDOW must be a positive integer")
+endif()
+math(EXPR _krw_p2 "${KEY_REPLAY_WINDOW} & (${KEY_REPLAY_WINDOW} - 1)")
+if(KEY_REPLAY_WINDOW LESS 128 OR NOT _krw_p2 EQUAL 0)
+  message(FATAL_ERROR "KEY_REPLAY_WINDOW must be a power of two >= 128")
+endif()
+
+# Re-key must finish within its lead window - KEY_REKEY_WATERMARK node keys worth of packets -
+# before the batch exhausts and TX fails closed. dev.c only evaluates the watermark once per
+# FLOW_WM_CHECK writes, so a lead below ~2x that leaves a high-rate flow no room to complete the
+# exchange. Production defaults are vast; this guards under-sized (test) geometries.
+if(KEY_REKEY_WATERMARK GREATER 0)
+  math(EXPR _rk_wm_check "1 << ${KEY_REKEY_WM_CHECK_BITS}")
+  math(EXPR _rk_lead
+    "${KEY_REKEY_WATERMARK} << (${KEY_LEAF_BITS} + ${KEY_NODE_BITS})")
+  math(EXPR _rk_min "2 * ${_rk_wm_check}")
+  if(_rk_lead LESS _rk_min)
+    message(WARNING
+      "Re-key lead is ${_rk_lead} packets vs the watermark check interval "
+      "${_rk_wm_check}; a high-rate flow may exhaust its key batch before the "
+      "re-key completes (TX fails closed until it does). Raise KEY_LEAF_BITS, "
+      "KEY_NODE_BITS, or KEY_REKEY_WATERMARK.")
+  endif()
+endif()