* setting up framework for Regions, TransportKeys, etc

src/helpers/TransportKeyStore.cpp

@@ -0,0 +1,44 @@
+#include "TransportKeyStore.h"
+#include <SHA256.h>
+
+uint16_t TransportKey::calcTransportCode(const mesh::Packet* packet) const {
+  uint16_t code;
+  SHA256 sha;
+  sha.resetHMAC(key, sizeof(key));
+  uint8_t type = packet->getPayloadType();
+  sha.update(&type, 1);
+  sha.update(packet->payload, packet->payload_len);
+  sha.finalizeHMAC(key, sizeof(key), &code, 2);
+  return code;
+}
+
+int TransportKeyStore::loadKeysFor(const char* name, uint16_t id, TransportKey keys[], int max_num) {
+  int n = 0;
+  for (int i = 0; i < num_cache && n < max_num; i++) {  // first, check cache
+    if (cache_ids[i] == id) {
+      keys[n++] = cache_keys[i];
+    }
+  }
+  if (n > 0) return n;   // cache hit!
+
+  if (*name == '#') {   // is a publicly-known hashtag region
+    SHA256 sha;
+    sha.update(name, strlen(name));
+    sha.finalize(&keys[0], sizeof(keys[0].key));
+    n = 1;
+  } else {
+    // TODO:  retrieve from difficult-to-copy keystore
+  }
+
+  // store in cache (if room)
+  for (int i = 0; i < n; i++) {
+    if (num_cache < MAX_TKS_ENTRIES) {
+      cache_ids[num_cache] = id;
+      cache_keys[num_cache] = keys[i];
+      num_cache++;
+    } else {
+      // TODO: evict oldest cache entry
+    }
+  }
+  return n;
+}